Physics of Complex Colloids: Equilibrium and Driven
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Self-organisation in complex colloids
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Final Report Summary - COMPLOIDS (Physics of Complex Colloids: Equilibrium and Driven)
The present document summarizes the progress made in all aspects of the ITN-COMPLOIDS from its beginning and during its second running period: November 1, 2011 to October 31, 2013.
Research in all Nodes of the ITN-COMPLOIDS has been running at a very high level, advancing the knowledge on cutting-edge problems associated with the Network and offering the involved Marie-Curie-Fellows training through research at the highest level. There was one Node, namelySchlumberger (SCR), which had employed the one Experienced Researcher (ER) during the first period and therefore has not been actively involved in further research activities of the Network.
Nevertheless, SCR remained an active member of the Newtork, participating in all Annual Meetings and being involved in all other aspects.
The successful execution of the research program set forth in Annex I of the COMPLOIDS-Network is amply documented by the large number and the very high quality of scientific publications that appeared in the most highly regarded international Journals. Furthermore, it has led to either the completion of the Doctoral Theses of the ESR’s and the granting of their Ph.D. Degrees or to the final stage of the same (see Section B below). As a general statement, the scientific goals of the Network have been not just achieved but even surpassed on a number of cases. A multitude of new collaborations and connections at the European level has emerged, strengthening thereby the presence of EU-based research in the field of soft matter science and forming the seed for new collaborative efforts in the future.
All ESR’s and ER’s of COMPLOIDS have received top-level training in cutting-edge concepts and methods in theoretical, computational and experimental aspects of modern research in soft matter science as a result of their involvement in research. They have coauthored the publications that came out of their research and they have either already obtained their Ph.D. degrees or they will be doing so in the course of 2014. (Please note that COMPLOIDS-recruitment took place around November 2010 and in the majority of cases, a Ph.D. degree requires 3.5 years or research before it can be awarded).
In addition to training through research, COMPLOIDS offered additional training in specialized scientific training (T) and transferrable-skills (S) modules, which was open also to non-COMPLOIDS participants. All scientific (T)-training modules were held by COMPLOIDS PI’s themselves, whereas for the soft-skills (S) modules, external experts were called-in in some cases to share their knowledge with the COMPLOIDS-Fellows. All T-modules have been thoroughly evaluated by the participants, using professional questionnaires. The results of the evaluation can be obtained from the Training Coordinator of the COMPLOIDS-Network, Professor Primož Ziherl (JSI-Node).
The COMPLOIDS-Enrico-Fermi Summer School 2012
A major training event has been the organization of a highly prestigious Enrico Fermi Summer School with the title “Physics of Complex Colloids”, which took place under the auspices of the Italian Physical Society (SIF) in Villa Monastero, Varenna, Italy, in the period July 3 – 13, 2012. It has been organized by three COMPLOIDS Principal Investigators: Professor Clemens Bechinger (USTUTT), Professor Francesco Sciortino (UNIROMA1), and Professor Primož Ziherl (JSI).
The School addressed experimental, theoretical, numerical results and methods. The topics of the lectures covered a broad spectrum of aspects starting from the synthesis of colloids and their use in commercial products. The School was designed as a series of minicourses, most of which consisted of five or three lectures. The minicourses were complemented by seminars addressing selected recent advances in the field and by poster presentation of the participants.
There were 9 full-time lecturers, namely:
• Christos N. Likos, Universität Wien;
• Gerhard Nägele, Forschungszentrum Jülich;
• Daan Frenkel, University of Cambridge,
• Emanuela Zaccarelli, Università di Roma La Sapienza;
• Roberto Piazza, Politecnico di Milano;
• Brian Vincent, University of Bristol;
• Larry A. Hough, University of Pennsylvania;
• Christian Van den Broeck, Hasselt University;
• Wilson C. K. Poon, University of Edinburgh
In addition, the Summer School featured 6 seminar speakers, namely:
• Paul Chaikin, New York University;
• Marjolein Dijkstra, Utrecht University;
• Matthias Fuchs, Universität Konstanz;
• Arjun G. Yodh, University of Pennsylvania;
• E. Trizac, Université Paris Sud;
• Peter G. Vekilov, Univeristy of Houston
65 students from around the globe participated, turning the Summer School into a major success. As evidence of recognition of the performace of the Summer School, the Italian Physical Society has solicited the organization of a Summer School of a similar content during Summer 2015. This has now been indeed approved by the SIF and a new Enrico Fermi Summer School on Complex Colloids will take place in July 2015, organized this time by the COMPLOIDS Principal Investigators Christos Likos (UNIVIE), Francesco Sciortino (UNIROMA1) and Primož Ziherl (JSI).
The proceedings of the summer school, a lasting 612-page deliverable of the COMPLOIDS School, were published in 2013. We expect the book to become a standard reference work for training of future generations of young soft matter scientists and we consider it to be a lasting legacy of COMPLOIDS to the scientific community.
The COMPLOIDS-Conference 2013
A major event that carried particular significance in both dissemination and in opening-up of COMPLOIDS to the broad scientific community was the COMPLOIDS-International Conference, which took place May 14-18, 2013, in Ljubljana (http://www.comploids2013.si). The main scientific focus of the conference was the current stage of soft matter science and colloidal physics including rheology, colloids in external fields, self-assembly, arrested states, liquid-crystal colloid dispersions, active colloids, and applications.
UNIVIE collaborated with: UEDIN on anisotropic, magnetic colloids; UCAM on cluster-forming colloids and many-body effects for magnetic colloids; JSI on connections between microscopic theories and elasticity approaches for soft colloids; USTUTT on transport through porous materials;
TUW on cluster-forming colloids and colloids under shear; Uniroma1 on soft glasses; FORTH on telechelic polymers and on soft glasses.
UEDIN collaborated with: UCAM on simulations of flow; CNRS on nanoemulsions; USTUTT on binary critical mixtures; TUW on polymer adsorption on surfaces; Uniroma1 on gels and glasses;
SCR on error analysis studies and development of LUDWIG LB code.
UCAM collaborated with: ULJU on self-assembly of magnetic colloids; JSI on self-assembly and elastic properties of clusters of magnetic colloids; USTUTT on active Brownian motion and transport through porous media; SCR on electrokinetic effects in porous media.
ULJU collaborated with: JSI on many-body effects in 2D-phases of elastic, soft colloids; CNRS in microfluidics; TUW on confinement-induced 2D-phases in magnetic colloids;
CRPP collaborated with: RHODIA on colloidal assemblies for acoustic materials.
JSI collaborated with: USTUTT on active Brownian motion and electrostatics in inhomogeneous media; TUW on many-body interactions among elastic objects and on ordering of magnetic colloids;
USTUTT collaborated with: TUW on transport through porous materials.
UNIROMA1 collaborated with: FORTH on soft glasses and rheology.
Cooperations with associated partners (in brief):
UNIVIE with A.Z. Panagiotopoulos (Princeton) and C. Dellago (U. of Vienna).
UEDIN with I. Pagonabarraga (Barcelona), D. Pine (NYU), and A.Z. Panagiotopoulos (Princeton).
UCAM with E. Trizac (Paris), I. Pagonabarraga (Barcelona), B. Rotenberg (Paris).
JSI with R. Kamien (U. of Pennsylvania) and E. Trizac (Paris).
USTUTT with S. Dietrich (Stuttgart).
FORTH with A.Z. Panagiotopoulos (Princeton).
No issues of conflict regarding Ethics or Equal Opportunity have been raised during this period of activity of the Network. All decisions regarding longer-term planning and activties of the Netwrok have been discussed openly and publicly during the Annual Meetings and they have been approved by the General Assembly in a public vote.
Overall Project Summary
In terms of overall research performance, the outcomes of COMPLOIDS have been truly outstanding. The milestones been not just fulfilled, but in many cases they have been even surpassed by research results that went beyond the originally set goals, opening up new avenues of research in the area of Soft Condensed Matter Physics. This is amply demonstrated by the number of publications that came out of COMPLOIDS-research in highly competitive, international, peer-reviewed journals, with about 20% of those having appeared in the top Journals in the field (Nature, Science, PNAS, Physical Review Letters, Nano Letters, ACS Nano). A summary of the Highlights is given below, broken down in the participating Nodes of the full COMPLOIDS-partners.
Node 1, University of Vienna (UNIVIE)
The UNIVIE-node has been mostly involved in investigations of the self-assembly and glassy dynamics of soft, deformable colloids and of associating colloids, having as main collaborators within COMPLOIDS the nodes: N5 (JSI), N8 (TUW), N9 (UNIROMA1), N10 (FORTH) as well as the Associated Partner PU (Princeton University, Prof. A. Z. Panagiotopoulos).
In Project P8 on telechelic star polymers (TSP) have been investigated along two parallel and complementary lines of research. In close collaboration with Prof. Panagiotopoulos at Princeton, the PI of the UNIVIE-Node (C. N. Likos) and the COMPLOIDS-ESR Christian Koch have launched extensive many-body lattice simulations to investigate the phase behavior and the self-organization of a variety of TSP-architectures, in which the degree of amphiphilicity, the functionality and the bending rigidity have been varied. It has been established that the fraction of attractive sites along the polymer chains determines the overall phase behavior of the system, whereupon macroscopic phase separation results when the majority of monomers is attractive whereas self-organization into spherical micelles, wormlike micelles and system-spanning, percolating networks obtains when the minority of monomers is attractive. Rigidity of the chains brings about a rich phase diagram with self-organization into a variety of ordered phases, in addition to the gas-liquid coexistence (see Fig. 1 below and Refs. [1,2]).
In parallel, a large-scale coarse-graining strategy has been developed and employed in collaboration with Dr. Barbara Capone in the Likos-group in Vienna. Here, the long polymer chains on each TSP have been replaced by systematically coarse-grained soft blobs, which facilitate the simulation of big systems. TSP’s have been shown to be versatile, self-organized soft patchy particles which can be used as building blocks for the targeted, selective, and scalable self-assembly of ordered crystals (see Fig. 2 below and Refs. [3,4]). These developments brought about close connections with work of the uniroma1-Node on hard patchy colloids and resulted as well in the development of a new research line in Vienna. Indeed, Dr. Capone has been awarded a prestigious three-year APART-Fellowship of the Austrian Academy of Sciences to pursue further work on the topic, whereas Dr. Lorenzo Rovigatti from the University of Rome will soon be joining the Likos-group at UNIVIE as a Postdoctoral Research Associate with the goal of bridging the gap between hard and soft patchy colloids.
please see attached graphics
Fig. 1: The phase diagram of rigid TSP’s with ten arms and 50% attractive monomers (left). Wormlike micelles built by TSP’s with six arms and 40% attractive monomers (right).
please see attached graphics
Fig. 2: The morphological diagram of TSP’s as soft patchy particles, and its dependence on number of arms f and degree of amphiphilicity α (left). Simulation snapshot of a diamond crystal built by TSP’s (right).
In Project P11, cluster crystals, a novel phase co-predicted by the PI a few years ago on the basis of generic, pair-potential models, were realized in microscopic, monomer-resolved simulations of amphiphilic dendrimers , providing a breakthrough in research in this direction, which resulted not only in a high-impact publication but also in extensive commentary as a News & Views-article on this work in Nature . Fig. 3 shows simulation snapshots of this unusual, cluster crystal, whose microscopic realization in silico opens the way for its experimental realization in follow-up work, in collaboration with experimentalists in the Jülich Research Center (Germany). Further collaborative work on the shear- and transport flow of cluster crystals has been performed in collaboration with the TUW-Node and it will be highlighted there.
please see attached graphic
Fig. 3: Monomer-resolved snapshot of a cluster crystal of amphiphilic dendrimers [(a)]; the centers of mass of the same, together with spheres showing their typical deviations from the equilibrium positions .
Daniela Marzi, also a UNIVIE-Node ESR of COMPLOIDS, has worked on the glassy behavior of soft and hard colloidal mixtures, in collaboration with the FORTH-Node and the topic will be highlighted in the corresponding section. Collaborations with the JSI-Node on soft colloid-elasticity will also be discussed under the JSI-Section.
1. C. Koch, C. N. Likos, A. Z. Panagiotopoulos, and F. LoVerso, Molecular Physics 109, 3049 (2011).
2. C. Koch, A. Z. Panagiotopoulos, F. Lo Verso, and C. N. Likos, Soft Matter 9, 7424 (2013).
3. B. Capone, I. Coluzza, F. Lo Verso, C. N. Likos, and R. Blaak, Physical Review Letters 109, 238301 (2012).
4. B. Capone, I. Coluzza, R. Blaak, F. Lo Verso, and C. N. Likos, New Journal of Physics 15, 095002 (2013).
5. D. A. Lenz, R. Blaak, C. N. Likos, and B. M. Mladek, Physical Review Letters 109, 228301 (2012).
6. F. Sciortino and E. Zaccarelli, Nature 493, 30 (2013).
Node 2, University of Edinburgh (UEDIN)
ESR Giulia Foffano carried out simulation studies of active fluids. These are suspensions of particles that use their own energy in order to do work. Examples can be found mainly, even though not solely, in biological contexts. Typically they are bacterial or algae suspensions, and the actomyosin solution. These out-of-equilibrium materials show a range of novel properties that in large extent still are to be investigated. As it is currently done in soft matter physics, one could think of using colloids as probes to investigate the behavior of active fluids at the micron scale. Giulia carried out simulations of micro-rheology experiments in active fluids, which show a behavior in striking contrast with the one of their passive analogue. In particular, she interpreted her results via an effective viscosity by analogy to Stokes law, and she found an important dependence on the probe size [1, 2] and a region of instability characterized by a steady state of negative drag . Her subsequent work focused on the aggregation of many colloids in active materials.
please see attached graphics
Fig. 4: Simulation snapshots of a colloidal particle being dragged through an active nematic liquid crystal. The color-coding of the background expresses the orientation of the latter, with red denoting an orientation parallel to the drag force (horizontal).
The research of ESR Niek Hijnen included an experimental study of three-component systems consisting of colloidal particles in a partially miscible binary liquid mixture in an unusual regime. The colloids are charge stabilized in the separate liquids, and in the phase-separated liquid mixture they are confined into one of the phases, demonstrating complete wetting by this (colloid-preferred) component. First, he showed that these systems often exhibit partial aggregation, leaving a fraction of the colloids stable in the supernatant, as the binodal of the liquid mixture is approached parallel to the liquid composition axis. Compared to previous observations in similar systems , the aggregation behavior is different and sets in much further from the liquid-liquid binodal. The effect involves adsorption of this component onto particles, eventually leading to capillary condensation as adsorbed layers meet. Second, he used a system where aggregation only occurs very close to the liquid-liquid binodal, and set the liquid composition poor in colloid-preferred component to confine colloidal rods  into a small volume by a rapid temperature quench into the two-fluid region. This way the rods are forced to assemble into (ordered) liquid crystalline phases (nematic and smectic) or into (disordered) percolating networks.
please see attached graphic
Fig. 5: Picture of a bijel with rod-shaped colloids packed on its surface.
ER Rim Harich investigated gels as they sediment under gravity. Gels are encountered daily in products ranging from yoghurt and pudding to diapers and contact lenses. They are formed by a percolating network of attractive particles, which can be colloids, nano particles, proteins or other molecules. In some gels only a very small fraction of the volume is taken up by this network. This system spanning network can be very rigid or very fragile depending on the attraction strength, particles size and density. Colloidal gels are out of equilibrium structures. Gels are prone to collapse (syneresis, compression) which is often hindering product development. The system Rim studied consists of PMMA colloids in decalin with a diameter 652 nm and a polydispersity of 5%. A polymer with a radius of gyration 45 nm thus the size ratio between the polymer and the colloid is 0.07. The gravitational length of the colloids is 110 nm. Data take the form of movies of sedimenting samples from which we extract the height of the sediment as a function of time. The sample shown below is just in the (metastable) gas liquid coexistence regime. She concluded that:
• Gels form when the spinodal crosses the attractive glass line.
• Gels have different collapse mechanisms depending on sample size, colloid volume fraction, attraction strength and quench history.
• At low colloid density the gels are most likely destroyed by gravity before they percolate. At higher volume fractions the gel resist gravity for a short time before collapsing.
1. G. Foffano, J. Lintuvuori, A. Morozov, K. Stratford, M. E. Cates, and D. Marenduzzo, European Physical Journal E 35, 9775 (2012).
2. G. Foffano, J. Lintuvuori, K. Stratford, M. E. Cates, and D. Marenduzzo, Physical Review Letters 109, 028103 (2012).
3. D. Beysens and T. Narayanan, Journal of Statistical Physics 95, 997 (1999).
4. N. Hijnen and P. S. Clegg, Chemistry of Materials 24, 3449 (2012).
Node 3, University of Cambridge (UCAM)
Project P1: The original Project P1 that can be found in Annex I has been expanded and modified with the informed consent of the previous COMPLOIDS‐Project Officer, Dr. Joanna Sowinska, who has been notified on this change on January 18, 2010, through an official letter of the Coordinator (available upon request).
The electrokinetic effect is the underlying mechanism allowing for the seismo-electric exploration of rocks used in oil industry. The flow in heterogeneous porous media is, however, a difficult problem, which is still poorly understood. PI Daan Frenkel and two associate partners of COMPLOIDS, Ignacio Pagonabarraga and Benjamin Rotenberg, have performed coarse-grained numerical simulations to study how the flow in porous media is related to the charge distribution . We designed a Hybrid Lattice Scheme based on the Lattice Boltzmann method, which turns out to be an efficient tool to describe the porous flow. We (A. Dobrinescu, J. Dobnikar and D. Frenkel) then proceeded by closely evaluating the relevant interactions occurring in heterogeneous electrolyte solutions. We have designed a model to simulate binary liquid solvents and to evaluate the electrostatic interactions between charged objects immersed in such solvents. By coupling the Poisson-Boltzmann description of ionic distribution to an Ising-like model for the domain distribution of water and oil, we studied electrostatic interactions and ion distribution in colloids immersed in critical water-oil mixtures. We are interested in exploring the influence of absorption properties and the ion-liquid coupling on electrostatic interactions. The occurrence of wetting transitions affects the structure of the electrostatic double layer formed at interfaces and changes the location of the critical point. Its effect on fluctuations in confined systems is relevant for studying Casimir-like forces due to thermal fluctuations. The simulations will be further exploited to emphasize many-body effects and hydrodynamic interactions. Consequently, the effective potentials obtained are useful for further studies on phenomena specific to porous media, such as capillarity or imbibition. Milestones M1, M2 and M3 have been mostly achieved. Recently, electrokinetic Lattice Boltzmann-based simulations have been set up in order to study the multipolar interactions and ion dynamics in solutions of penetrable soft charged colloids both, in bulk as well as in confined geometries. The work on this project, which, among others, will lead towards achieving the last milestone M4, is ongoing and the final results are expected to be available in early 2014. During the execution of the proposed project new exciting problems have been identified and we started to work on them. Specifically, we explored the solid-liquid phase behavior of charged colloids with short-range attractions (cooperation with E. Del Gado, ETH Zurich) relevant for a broad range of applications, among them settling of cement. We also started exploring the dynamic assembly of magnetic colloids in time-dependent external fields (T. Mohorič, R. Alert Zenon) and ordering and microrheology of confined and arrested magnetic colloids: in cooperation with C. N. Likos (UNIVIE-Node), J. Horbach (University of Düsseldorf), J. Brujič and E. Vanden-Eijnden (New York University).
Project P23: In the first part, in collaboration with F. Matthäus (Heidelberg) and T. Curk (Maribor and Cambridge), a combination of mathematical analysis and numerical simulations was applied to explore the chemotactic motility of E. coli. Stochastic fluctuations affecting the chemotactic signaling processes can enable the bacteria to perform Lévy walks, which, in turn, presents and evolutionary advantage when trying to survive in harsh environments. We have explained  the emergence of the Lévy walks by a rigorous mathematical theory showing that the shifts in the internal enzyme concentrations following the stochastic fluctuations lead to the superposition of exponential distributions into a power-law. We have later developed a model , where we couple the chemotactic signaling pathway to a multi--flagellar description of cell propagation. Based on this model we determined the limits of logarithmic nutrient sensing obeying the Weber law and defined a small set of relations constituting a coarse grained model of bacterial chemotaxis. We have also studied the mechanisms leading to bacterial pattern formation. Specifically, we focused on the interplay of sensing the ambient and secreted nutrients and on the role of density fluctuations in emergence of bacterial clusters and patterns . After studying the planktonic motility of mostly E. coli in bulk, we focused on the behavior of bacteria at surfaces, where another type of motility mediated by type-IV pili becomes more relevant. Understanding the surface twitching motility of bacteria like P. aeruginossa is crucial to understand the formation of bacterial biofilms. Kinetic Monte Carlo simulations of the twitching motility have been set up. The trajectories from the simulations were confronted with experimental results from the lab of G. Wong (UCLA, USA) resulting in the possibility to determine the value of several previously unknown parameters governing surface organization of bacteria and to discuss the evolutionary advantages of the specific architecture enabling optimal motility. A joint theoretical--experimental manuscript is currently being finalized.
Finally, in cooperation with COMPLOIDS associated partner Ignacio Pagonabarraga, we have started exploring the statistical physics of colloidal interactions mediated by active particles (J. Codina), which can be seen as very coarse-grained models of swimming bacteria and also a model for synthetic microswimmers.
please see attached graphic
Fig. 6: Pattern formation of E.coli on agar as a result of the interplay between sensing the ambient and secreted nutrient. The large-scale numerical simulations were performed in cooperation with the COMPLOIDS partners in Edinburgh, Ref. .
The group of Erika Eiser at UCAM has significantly contributed to work packages W2, W3, and W4 (Soft deformable colloids, confined colloids, driven colloids respectively), publishing 8 articles in high impact journals, and with one submitted journal article and another one close to submission.
We exploit the high specificity of DNA, grafted to colloids, to drive colloidal aggregation leading to new types of amorphous materials that may have wide application in the development of photonic materials and novel 3D-battery materials. To this end we were the first to created two interwoven yet independent percolation colloidal gels with well-defined porous structure, which we call bigels. [5-7] These systems are strongly out of equilibrium systems with interesting aging dynamics. This work was done in collaboration of the group of Prof. Giuseppe Foffi (EPFL, Lausanne and University Paris 6), who did complementary simulations allowing us to explore a wide range of parameter sets.
In the context of confinement effects we studied the aggregation behaviour of ‘heavy’ silica particles sedimented onto a mechanically ‘soft’ surface made of cross-linked polymers. In rheology and video-microscopy experiments we demonstrated that when the elastic modulus or the crosslink-density of the polymer hydrogel falls below a certain value, negatively charged silica beads start to aggregate, although they usually repel one another in aqueous bulk solution due to Coulomb repulsion. We developed a predictive theory and tested this with simulations to understand the cause of the aggregation. Our theory clearly describes the aggregation in terms of weak attraction between the colloids and the substrate as well as the ‘softness’ of latter (Figure 7 and Refs. [8-11]). Our finding may be relevant to industrial applications, such as fillers in rubbers as well as aggregation of proteins on a soft cell membrane. The theory was developed in collaboration with Dr. Alessio Zaccone (Univ Cambridge), and Prof Seth Fraden (Brandeis Univ, Boston, USA) advised us on the experiments.
please see attached graphic
Fig. 7: Left: Microscope images showing the aggregation of 1 µm large silica beads on a ‘soft’ surface in time (Bulk modulus of the cross-linked surface was about 10 Pa). The insert (a) is a blow-up of one of the aggregates formed after 30 minutes, showing locally hexagonal order. Right: Top and side view of coarse grained simulation snapshots: The polymer layer is simulated as an array of ‘soft’ beads connected to their next neighbours via an-harmonic springs. The lower layer of polymer beads (red) is stabilized to prevent collapse of the layer. The top beads (gray) are only linked through springs to the lower one but not to those in the same layer reflecting the ‘roughness’ of the layer. The silica beads, here presented in pink, are free to fluctuate on the surface but experience their natural gravitational pull downwards as well as a weak attraction to the polymer beads. Images are taken from the PhD thesis of Dr Lorenzo di Michele.
The group of Pietro Cicuta at UCAM has, through the work of ESR Nicolas Bruot, addressed the question of emergent dynamical patterns in non-equilibrium (driven) colloidal systems. This is a really active area at the moment, with major emphasis on swimming systems, and swarming patterns. The approach has been a bit different, looking instead at the dynamical patterns of phase oscillators with fixed mean position. This is relevant as a model for biological arrays of motile cilia, and is relevant technologically in the context of surface-driven flows, by micropumps. We discovered (and explained quantitatively) the key role of the shape of the potential that drives the phase oscillators, and of their arrangement in space. The collective dynamics (which can be waves, or local “dynamical motifs”) is very sensitive to both. As very simple examples, we can now predict how to set up a pair of oscillators so that they will spontaneously beat in phase or in antiphase; we have also discovered “design criteria” to maximize the hydrodynamic coupling.
Moreover, COMPLOIDS-funding was essential in providing some funds for hardware infrastructure which also benefited other students in the lab, but most importantly the ITN guaranteed regular meetings with the network of leading EU groups in the area of colloids and self assembly, providing a strong intellectual backbone on which to pursue a range of scientific ideas [12-15]. This enabled the PI (Pietro Cicuta) to suggest as undergraduate thesis projects, or investigations within other PhD work, a range of investigations that fitted the Comploids remit. This resulted in a range of discoveries, ranging from the interaction of particles on liquid surfaces (which is central to WP3, P18), to the self-assembly of particles under external fields (WP1, P7).
please see attached graphic
Fig. 8: A playful experiment, in which 5 colloids, interacting only via hydrodynamic flow, converge into an in-phase steady state. The colloids are driven on predefined circular trajectories, by optical traps, using a fast feedback loop to maintain a constant force on each particle.
1. B. Rotenberg, I. Pagonabarraga, and D. Frenkel, Faraday Discussions, 144, 223 (2010).
2. F. Mattheaus, M. S. Mommer, T. Curk, and J. Dobnikar, PLoS One 6, e18623 (2011).
3. T. Curk, F. Matthaeus, Y. Brill-Karniely, and J. Dobnikar, Advances in Experimental and Medical Biology 736, 381 (2012).
4. T. Curk, D. Marenduzzo, and J. Dobnikar, PLoS One (in press),
5. L. Di Michele, D. Fiocco, F. Varrato, S. Sastry, E. Eiser, G. Foffi, Soft Matter (submitted, 2013).
6. L. Di Michele, F. Varrato, J. Kotar, S. H. Nathan G. Foffi, E. Eiser, Nature Communications 4, 2007 (2013).
7. F. Varrato, L. Di Michele, M. Belushkin, N. Dorsaz, S.H. Nathan, E. Eiser, G. Foffi, Proceedings of the National Academy of Sciences of the U.S.A. 109, 19155 (2012).
8. L. Di Michele, A. Zaccone, and E. Eiser, Proceedings of the National Academy of Sciences of the U.S.A. 109, 10189 (2012).
9. T. Yanagishima, L. Di Michele, J. Kotar, and E. Eiser, Soft Matter 8, 6792 (2012).
10. T. Curk, A. de Hoogh, F. J. Martinez-Veracoechea, E. Eiser, D. Frenkel, J. Dobnikar, and M. E. Leunissen, Physical Review E 85, 021502 (2012).
11. L. Di Michele, T. Yanagishima, A. R. Brewer, J. Kotar, E. Eiser and S. Fraden, Physical Review Letters 107, 136101 (2011).
12. E. Aumaitre, S. Wongsuwarn, D. Rossetti, N. D. Hedges, A. R. Cox, D. Vella, and P. Cicuta. Soft Matter 8, 1175 (2012)
13. S. Wongsuwarn, Y. Li, P. Cicuta, and E. M. Terentjev, Soft Matter 9, 235 (2013).
14. N. Bruot and P. Cicuta, Journal of the Royal Society: Interface 10, 20130571 (2013).
15. D. Paul, S. Achouri, Y.-Z. Yoon, J. Herre, C. E. Bryant, and P. Cicuta, Biophysical Journal 105,1143 (2013).
Node 4, University of Ljubljana (ULJU)
Project P5 focused on the development of versatile techniques for synthesis of aspherical colloidal particles. Within this project our group is intensively collaborating in the development of UV mask less prototyping techniques with industrial partners Aresis d.o.o. and LPKF d.o.o. As a result a rapid prototyping system (Protolaser PLD) was developed and is now operational. The system is being evaluated and used in our and several other evaluation laboratories (IJS Ljubljana Slovenia, PZH Garbsen Germany).
In development of rapid prototyper a laser beam steering technique based on acousto-optic deflection has been successfully applied and optimized for micron scale structuring of either micro fluidic components or arbitrary shaped particles. Comploids ESR Ivna Kavre is now routinely using the technique in combination with different approaches of particle molding and separation. Results so far demonstrate that large scale production of particles is possible and the stability of these particles is adequate. With respect to work progress on project P5 it can be stated that milestones M1 (optimization of micro structuring) and M2 (scale and stability evaluation) have been fully achieved (Fig. 1).
Much success has been achieved in multistep structuring (milestone M3) which enables the production of functionalized (magnetic) aspheric particles. Aspheric particles produced with above mentioned approach have been successfully used in experiments described in papers listed in section References under [1-4] (milestone M4).
please see attached graphic
Fig. 9: a,b,c) SEM images of SU-8 structures – photoresist thickness ~9m, d) bright field image of PDMS particles captured on a thin PDMS film, e) PDMS particles on AZ photoresist, f) magnetic particles dispersed in water.
Project P13 is part of an ongoing research broadly termed “interparticle interaction engineering” in colloidal systems. The main goal of this research is to develop different techniques of inducing interparticle interactions either by external fields, confinement or both. Much success has been achieved with super paramagnetic colloids of aspherical shape.
One way to achieve complex interparticle pair potential is to combine the magnetic interaction with a screened electrostatic one. To this end, custom-made sample cells were developed, which incorporate microelectrodes structured so as to produce local electric field of desired shape and strength. It has been demonstrated that a quadrupolar dielectric bottle can be used to apply a dielectrophoretic torque and thus enable a precise control over orientation of colloidal clusters. This approach has been used in experiments, demonstrating a precise control over micro fluidic pumps based on magnetically rotated colloidal triplets .
In second type of experiments, an external magnetic field in combination with particle confinement was used to produce a core-softened interparticle potential. Phase diagrams showing colloidal phases with respect to particle density and degree of confinement were measured. Results are being analyzed with theoretical models developed by collaborating nodes (UCAM, JSI: [5,6] and UCAM, UNIVIE: ).
Application of newly developed techniques has enabled the production of aspherical magnetic particles. In preliminary experiments, we studied self-assembly scenarios on a small number of particles with triangular symmetry. These scenarios are governed by both the magnetic interaction and shape of the particles. First results show that assembled structures can incorporate symmetries which are not achievable with spherical particles (Fig. 3), which is of great interest in the field of meta-materials and photonic crystals.
please see attached graphic
Fig. 10: Small number of magnetic particles in the presence of the magnetic field. Final arrangements indicate that the junction with arm ends is energetically one of the most stable. For three c) and four d) particles the symmetric ring-configuration is be stable, e) the same configuration for five particles is unstable. These results correspond well to results of numerical simulations.
1. M. Vilfan, G. Kokot, A. Vilfan, N. Osterman, B. Kavčič, I. Poberaj, and D. Babić, Beilstein Journal of Nanotechnology 3, 163 (2012).
2. B. Kavčič, D. Babić, N. Osterman, B. Podobnik, and I. Poberaj, Microsystems Technology 18, 191 (2012).
3. G. Kokot, M. Vilfan, N. Osterman, A. Vilfan, B. Kavčič, I. Poberaj, and D. Babić, Biomicrofluidics, 5, 034103 (2011).
4. M. Vilfan, A. Potocnik, B. Kavcic, N. Osterman, I. Poberaj, A. Vilfan, and D. Babic, Proceedings of the National Academy of Sciences of the U. S. A. 107, 1844 (2012).
5. B. Kavčič, D. Babić, N. Osterman, B. Podobnik, and I. Poberaj, Applied Physics Lett.ers 95, 023504 (2009).
6. N. Osterman, D. Babić, I. Poberaj, J. Dobnikar, and P. Ziherl, Physical Review Letters 99, 248301 (2007).
7. K. Müller, N. Osterman, C. N. Likos, J. Dobnikar, A. Nikoubashman, and D. Babić, in preparation.
Node 5, Jožef Stefan Institute (JSI)
We have theoretically elaborated the continuum theory of cluster formation , extending the ideas proposed earlier to several more complex 2D and 3D geometries. Within this framework clusters formed by the colloidal particles are treated as regions of homogeneous density, and the evaluation of the overlap energy is reduced to a geometrical problem. Using this approach, we showed that the T = 0 phase sequence predicted by the continuum theory is consistent with that obtained using the genetic- algorithm search for the minimal-energy structures. From the technical perspective, the detailed analysis of the continuum theory is interesting because it demonstrates how the continuum theory can be applied to geometrically complex cluster forms and because it produces fairly reliable results at a fraction of the computational cost needed in a genetic-algorithm or a fully numerical minimization. The continuum approach is particularly suitable for the analysis of the structural behavior of broad-shoulder colloids where each particle interacts with many neighbors and a mean-field approximation is justified.
The continuum theory of cluster formation was also used to rederive and reassess the clustering criterion as well as the phase diagram of cluster-forming colloids. In Ref. , we applied the continuum theory to the 2D stripe cluster phase and we computed its free energy at T = 0. By extending it to finite temperatures by including the Carnahan-Starling type entropic contribution of the colloids’ hard-cores, we constructed the phase diagram, showing that the clustering only takes place at low enough temperatures and intermediate densities, which represents a qualitative deviation from the criterion based on the fluid- phase instability.
Elastic interaction between deformable colloids is a very interesting problem because it may explain the characteristic structural behavior of nanocolloidal particles based on macromolecular assemblies and self- assemblies. The structures formed by these systems are quite different from those found in classical, micrometer-size colloids often consistent with the hard-sphere paradigm. Experiments show that nanocol- loids often form open rather than close-packed lattices and their stability remains an open question. One possibility is the elastic interaction of the nanocolloids. But elastic deformation of deformable bodies is inherently non-local and non-pairwise additive, and thus many-body effects are expected to be important. In order to shed light on the many-body contact repulsion, we used a spring-and-plaquette model to explore the energy of elastic disks on simple 2D lattices . We showed that while in the moderate Poisson-ratio regime elastic repulsion does not depart considerably from the Hertzian pairwise additive model, the many-body effects are dominant in the incompressible limit. From these results, we were able to draw two important conclusions. Firstly, the notion of soft colloids is too broad in the sense that ma- terials with a large bulk modulus should be distinguished from materials where bulk and shear modulus are comparable. Secondly, an almost incompressible elastic particle surrounded by many neighbors will enter the hard-core-like regime at an smaller indentation compared to an identical particle having fewer neighbors. Thus a perfectly monodisperse ensemble of colloids may behave as an effectively polydisperse system, suggesting that soft colloids may be more difficult to crystallize.
In a combined experimental and theoretical project, we developed a methodology for the quantitative analysis of 3D shapes of lipid vesicles . A well-known tool to study 3D structures in colloidal science, confocal microscopy can also be the method of choice in other contexts. Here we used it to quantify the shape of vesicles formed by lipid bilayer membrane labeled with a fluorescent dye. From the 3D fluorescence intensity image, we extracted the shape of the membrane as a closed surface and we analyzed various morphometric parameters of the surface. We tested the methodology on simple shapes of isolated vesicles, investigating their stationary shapes and spontaneous shape deformations. We have mapped the phase diagram of the vesicles, focusing on the previously poorly quantified part occupied by non- axisymmetric shapes. The results are perfectly consistent with the Helfrich local bending elasticity as the widely accepted continuum model of membranes. Spontaneous shape deformations provided an additional insight into the mechanics of vesicles. Firstly, we were able to analyze the transient shapes forming the morphological pathway between two stationary shapes, and we found that they are consistent with the bilayer-couple theory. Secondly, we examined the possible scenarios of spontaneous shape deformations, concluding that the membrane must contain so-called area reservoirs on either monolayer. These postulated reservoirs are formed during bilayer rehydration, and they release excess lipids into either monolayer.
please see attached graphic
Fig. 11: Elastic energy density in disks of moderate (top row) and large Poisson ratio, the latter undergoing a transition to hard-core-like regime at large indentations (bottom right panel) .
1. A. Košmrlj, G. J. Pauschenwein, G. Kahl, and P. Ziherl, Journal of Physical Chemistry B 115, 7206 (2011).
2. P. Ziherl and R. D. Kamien, Journal of Physical Chemistry B 115, 7200 (2011).
3. A. Sakashita, N. Urakami, P. Ziherl, and M. Imai, Soft Matter 8, 8569 (2012).
4. A. Šiber and P. Ziherl, Physical Review Letters 110, 214301 (2013).
Node 6, Centre National de la Recherche Scientifique (CNRS)
In Project P7, we investigated the properties of dispersions of carbon nanotubes (CNTs) and graphene flakes. These particles have remarkable physical properties at the individual level and one of the key objectives was to control the large-scale ordering of these carbon-based particles under the form of liquid crystalline materials with unprecedented and original features [1-3]. The main achievements are summarized below:
• Improvements of order parameters of CNT liquid crystals
• First study of the surface conductivity anisotropy of CNT liquid crystal films
• Formulation of original liquid crystal phases made of reduced graphene oxide.
please see attached graphic
Fig. 12: Left- (a) Optical micrograph of an isotropic suspension of diluted graphene oxide (GO). The inset shows the same sample observed in between crossed polarizers.(b,d) Optical micrographs between crossed polarizers for concentrated GO (b) and reduced GO-BS (d) suspensions after a single ultracentrifugation at 210.000g during 60 min. Scale bar in panel d =400μm. (e−h) Corresponding SAXS 2D patterns for all graphene aqueous suspensions shown in the first row. The graphene concentrations are from left to right: 0.1 6.6 and 5.9 wt %. The materials in panels f and h exhibit “butterflies” patterns arising from nematic ordering. Right- SAXS spectra depicting the scattered intensity as a function of the scattering wave vector q for suspensions of reduced GO (RGO) at different concentrations. Sketch of the RGO flakes. Adapted from ref. .
In Project P19, we studied the behavior of solid microparticles adsorbed at liquid crystal-air interfaces. One of the goals of this project was to examine the interplay of capillary and elastic forces on the interactions of the colloids. The system consisted of free-standing smectic membranes into which micron-sized spherical and non-spherical particles could be efficiently trapped due to surface tension forces and elastic properties. Large menisci form around the inclusions if their size is larger than the film thickness. We found evidence of structured, striped patterns in the menisci upon temperature-induced phase transitions. Interferometric tools revealed that these stripes correspond to smectic layer undulations whose amplitude and wavelength depend on thickness gradients. The results were interpreted through a simple model. The general result is that a liquid meniscus is not always smooth but can be rough and structured due to an elasto-capillary coupling [4,5].
We further analyzed the behavior of ellipsoid-shaped particles in response to optical forces from a moderately focused laser beam. The particles were fabricated from micrometer-sized polymer spheres using a widespread mechanical stretching technique. Both prolate and oblate ellipsoids with dimensions between a few m and several tens of m were obtained. We studied the behaviors of these objects in a classical levitation experiment, with a vertical laser beam (waist diameter 3 m), in water. We collected many observations with particles of different aspect ratios located in different regions of the beam. We observed the particles’ responses in bulk water and close to a surface, which might be solid (water-glass) or fluid (water-air and water-oil interfaces).
Near the beam-waist, particles that were not too far from a sphere got trapped on the laser beam axis in static configurations, with their long axes lying vertical. Conversely, we found that particles of high ellipticity, either rod-like or disk-like, never came to static configurations: they were seen to undergo sustained oscillations, in the form of coupled translation and tilt motions.
We have proposed an interpretation of the observed dynamical behaviours on the basis of a simple 2-dimensional (2d) model, using the ray-optics approximation. For prolate ellipsoids and a simply parallel beam, the model indeed produced a bifurcation between static states and limit cycles when the ellipticity increases. As an essential outcome, the model showed that the non linear dependence of the radiation pressure forces versus the particle position and angle coordinates was enough to explain the oscillations.
please see attached graphic
Fig. 13: (a) Interferogram of a liquid crystal smC film (reflection mode). The interference fringes are not straight but are a bit wavy. T=40°C, scale bar: 13 m. Inset: Corresponding optical photograph in transmitted white light. The stripes can be clearly seen. Scale bar: 16:2 m. The arrow indicates the location of broad wrinkles in the interferogram.
(b) Associated color-coded image plot of the interface profile. The bottom graph shows the undulated meniscus profile along the oblique dashed line (region of broad stripes).
The 2d model can only predict static equilibriums and periodic dynamical states (limit cycles). Such states are indeed observed in experiments, but the 3-dimensional character of the real system generates more complex dynamics in certain cases. Using standard tools of non linear dynamics analysis, we indeed evidenced irregular dynamics akin to deterministic chaos with particles of various size parameters, at various altitudes in the laser beam. However, we were not able to evidence a simple route to chaos. We applied the levitation technique to a problem pertaining to physical chemistry of surfaces. We investigated how polystyrene particles, initially in bulk water, come to a static equilibrium across the water-air interface, in partial wetting configuration. We focused our study on possible differences between spheres and ellipsoids, because we suspected than the non planarity of contact lines on ellipsoidal bodies might cause a difference in the dynamics of the particle emersion, compared to spheres. In fact, the data that we collected showed that there was no real difference. We concluded that in all cases the dynamics of the contact line is mainly controlled by the pinning-depinning mechanism, in line with recently published results for spherical micrometre-sized spheres. This conclusion holds equally for spheres and ellipsoids, either prolate or oblate.
1. C. Zamora-Ledezma, C. Blanc, N. Puech, M. Maugey, C. Zakri, E. Anglaret, and P. Poulin, Physical Review E 84, 062701 (2011).
2. C. Zamora-Ledezma, N. Puech, C. Zakri, E. Grelet, S. E. Moulton, G. G. Wallace, S. Gambhir, C. Blanc, E. Anglaret, and P. Poulin, Journal of Physical Chemistry Letters 3, 2425 (2012).
3. C. Zakri, C. Blanc., E. Grelet,, C. Zamora-Ledezma, N. Puech, E. Anglaret,, and P. Poulin, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, 20120499 (2013).
4. B. M. Mihiretie, P. Snabre, J.-C. Loudet, and B. Pouligny, Europhysics Letters 100, 48005 (2012).
5. B. M. Mihiretie , J.-C. Loudet , and B. Pouligny, Journal of Quantitative Spectroscopy & Radiative Transfer 126, 61 (2013).
Node 7, Universität Stuttgart (USTUTT)
During the last four years, ESR Ivo Buttinoni studied the active Brownian motion of spherical and non-spherical self-propelled particles which move under bulk conditions but also in geometrically confined geometries. Active Brownian motion is currently attracting considerable interest from biological and physical communities. A paradigmatic example of such a motion is offered by chemotactic bacteria, e.g. Escherichia Coli. Their strategy to search for nutrients can be described as a sequence of “swims” and “tumbles,” i.e. rather straight trajectory segments and random reorientation events. In the presence of nutrient gradients, the frequency of such tumbles changes, which leads to motion either towards (chemo-attractants) or away (chemo-repellents) from the gradient. Inspired by chemotactic bacteria and cells, various artificial systems capable of performing active Brownian motion have been proposed. In particular, the use of phoretic forces allows the construction of propulsion mechanisms which do not rely on external fields and thus allow an autonomous motion which may provide interesting options for the localization, pick-up and delivery of microscopic and nanoscopic objects in liquid environments.
During his experiments, he developed a novel self-propulsion scheme which relies on the light-induced local demixing of a binary mixture close to its critical point. In contrast to other approaches, it does not require a “fuel” which becomes depleted during operation of the swimmers. When such Janus particles are suspended in a critical mixture of water and lutidine several degrees below the critical temperature TC = 307K, they undergo normal Brownian motion. However, when the entire sample is exposed to light which is only absorbed at the particle’s metal coating, a local demixing of the fluid occurs which eventually leads to a concentration gradient and thus to a phoretic self-propelling force. Since the concentration gradient is determined by the illuminating laser intensity, the phoretic force and in particular the persistence length can be continuously adjusted.
To understand, how microswimmers behave in the presence of additional, rigid obstacles he also investigated the influence of walls, cavities and periodic arrays of pillars, the latter being fabricated by soft lithography. Due to steric interactions with the swimmers, this leads to strong deviations from the bulk-swimming behavior. In particular, it could be demonstrated that, when the persistence length of the swimmer’s trajectories exceeds the mean distance between the pillars, they preferentially move along directions where they avoid collisions with other obstacles. This mechanism, which was here demonstrated for the first time, can be also exploited to sort swimmers according to their propulsion force.
Ivo Buttinoni also studied the effect of mutual collisions between microswimmers and how this affects their phase behavior. He could demonstrate that even in the absence of any alignment interactions, this can lead to a clustering of particles which becomes enhanced with increasing particle density and propulsion force. This dynamical phase transition into a dense phase is in exellent agreement with numerical simulations and suggests that short-ranged steric interactions are sufficient to create clusters in active systems [1,2].
Very recently, Ivo Buttinoni investigated also the motion of asymmetric self-propelled particles. The above swimming mechanism can be also applied to asymmetric, e.g. L-shaped particles which were fabricated by soft lithography (dimensions 9µm x 6µm). When such particles undergo active Brownian motion, their trajectories become circular indicating a torque acting on them. This torque is due to viscous forces originating from the friction with the surrounding solvent and leads to a radius of curvature being independent of the propulsion force, i.e. the particle’s velocity. When such particles encounter a lateral wall, their torque leads either to a stable sliding mode or a reflection, depending on their angle of incidence.
In her experiments, ESR Lamiss Zaidouny studied the phase behavior of a charge-stabilized two-dimensional colloidal crystal which is subjected to a one-dimensional, periodic light field. Such light fields are created by a scanned optical laser line which allows the variation of the periodicity without optical realignments. In contrast to optical interference patterns, this technique allows the in situ control of the periodicity without any optical realignment. In addition, potential landscapes with non-sinusoidal cross-sections and even non-periodic patterns can be created. In order to realize a wide range of line spacings relative to the lattice constant, she used a suspension of silica particles in bromobenzene as a solvent. Because of the Debye screening length of this system is about 4.6µm this results in the formation of crystals with lattice constants up to 20µm. Because the refractive index of bromobenzene is larger than that of the colloids, optical gradient forces lead to the attraction of particles towards regions where the intensity is smallest. Depending on the depth and periodicity of the laser potential, Lamiss observed the light-induced assembly of colloids into triangular, rhombic and square phases.
In addition to using one-dimensional periodic substrate potentials, Lamiss also investigated the effect of a quasiperiodic line pattern on the phase behaviour of a repulsive colloidal system. Interestingly, she observed, that the particles arrange in periodically spaced lines, whose spacing is neither determined by the mean particle distance nor the L and S spacing of a Fibonacci chain. The formation of periodic order on a quasiperiodic substrate potential can be understood by the concept of periodic averages structures, a concept which has been introduced to explain the phase transition between crystals and quasicrystals. Application of this concept to our experiments, reveals perfect quantitiative agreement and demonstrates that, despite its generic differences, strong links between periodic and quasiperiodic order exists .
please see attached graphic
Fig. 14: A one-dimensional quasicrystalline external field imposed on a two-dimensional colloidal assembly (upper right part) and the resulting colloidal arrangement (lower right part).
1. I. Buttinoni, J. Bialke, F. Kümmel, H. Löwen, C. Bechinger, and T. Speck, Physical Review Letters 110, 238301 (2013).
2. F. Kümmel, B. ten Hagen, R. Wittkowski, I. Buttinoni, R. Eichhorn, G. Volpe, H. Löwen, and C. Bechinger, Physical Review Letters 110, 198302 (2013).
3. L. Zaidouny, T. Bohlein, R. Roth, and C. Bechinger, Soft Matter (in press).
Node 8, Technische Universität Wien (TUW)
Work at the TUW-Node has focused on investigations of equilibrium and flow behavior of cluster-forming complex colloidal systems, both at microscopically-resolved and at the coarse-grained levels.
ESR Ioannis Georgiou worked on a monomeric model of the amphiphilic dendrimers (with a particular focus on fourth generation macromolecules) we have investigated the spatial and orientational correlations of these dendrimers over a representative range of densities (in the liquid regime) in extensive computer simulations. To this end we have extracted from the simulation data characteristic quantities that specify the size and the shape of the dendrimers. In combination with the radial and the orientational correlation functions these data provide evidence that these macromolecules do react on a density increase with distinct changes in their volume, their shape and their spatio-orientational correlations. From these data we could observe that with increasing densities particles tend to arrange in anti-nematic arrangements; from these findings we expect for even higher densities the formation of exotic ordered structures, such as the A15 lattice . This work was done in collaboration with PI Primož Ziherl at the JSI-Node.
please see attached graphics
Fig. 15 Simulation snapshot of two oberlapping amphiphilic dendrimers (left panel). Simulation snapshot of a two-dimensional confined system of cluster-forming ultrasoft particles (right panel).
ESR Marta Montes-Saralegui has investigated the hopping and diffusion processes of (mesoscopic) ultrasoft, cluster-forming particles in the explicit presence of a microscopic solvent. Assuming a simple functional form for the effective interaction of the particles we have carried out computer simulations, based on the multi-particle collision protocol (MPCD): this approach mimics faithfully the hydrodynamic interactions induced by the solvent particles. By evaluating the dynamic correlation functions of the solvent particles we could demonstrate that the presence of the solvent does have an important impact on the diffusion and on the hopping processes of the particles: this applies in particular to the diffusive behavior, to the angular orientation of the jump events, and to the spatial extent of these events. Extending our investigations to a binary mixture of ultrasoft particles (with one particle species being ultrasoft, but non-cluster-forming) we could show that due to the presence of the solvent diffusion and jump processes are distinctively different for the two particle species . Further, a two-dimensional system of ultrasoft, cluster-forming system has been exposed to compression via a barostat, realized by a bath of ideal gas particles, guaranteeing thereby constant pressure and constant temperature conditions. In ongoing investigations we identify the characteristic cluster-merging and particle hopping processes as the system is compressed.
ESR Arash Nikoubashman has performed out-of-equilibrium computer experiments on such systems. Using again MPCD-simulations, we have exposed cluster crystals to shear (Couette) and transport (Poiseuille) flow. In the case of shear flow we could identify a novel and universal response of systems of ultrasoft particles to steady shear: after a shear-banding regime at low shear rates, strings of particles parallel to the flow direction form as shear grows, which order on a hexagonal crystal in the gradient-vorticity plane. At even higher shear, lateral fluctuations of the strings, enhanced by hydrodynamics, lead to a disordered fluid state. Conversely, we could show that the nucleation rates of supercooled liquids can be dramatically accelerated via the shear-induced formation of an intermediate string pattern, which disaggregates after the cessation of shear, leading to the emergence of three-dimensional fcc order. Exposing our system to Poiseuille flow (induced via a pressure gradient) we established the emergence of a quantized flow pattern in which both the height and the width of the fluid stream display well-defined plateaus as a function of the applied pressure gradient. The resulting velocity profiles of the solvent closely resemble plug flow, an observation which can be explained by successive fluidization of the crystalline layers adjacent to the channel walls [3,4].
We have investigated the propagation of a single, neutrally buoyant rigid sphere under pressure-driven flow by means of extensive MPCD computer simulations. We first consider a system geometry consisting of two parallel plane walls and achieve very good agreement with experimental results for the average particle velocity. In the second part of our analysis we have simulated the flow of tracer particles through a hexagonal array of cylindrical obstacles whose axis lies parallel to the gradient-vorticity plane of the flow. We find that the presence of the obstacles causes a significant slowdown of the tracer particles and that their velocities respond in a highly non-linear way to an increasing pressure drop . This work has been performed in collaboration with PI Christos Likos from the UNIVIE-Node.
please see attached graphics
Fig. 16: Simulation snapshots of a cluster crystal sheared along the  direction, showing the formation of strings along the flow-gradient plane and their ordering into a triangular lattice on the vorticity-gradient plane.
1. M. Montes-Saralegui, A. Nikoubashman, and G. Kahl, Journal of Physics: Condensed Matter 25, 195101 (2013).
2. I. A. Georgiou, P. Ziherl, and G. Kahl, submitted (2013).
3. A. Nikoubashman, G. Kahl, and C. N. Likos, Physical Review Letters 107, 068302 (2011).
4. A. Nikoubashman, G. Kahl, and C. N. Likos, Soft Matter 8, 4121 (2012).
5. A. Nikoubashman, C. N. Likos, and G. Kahl, Soft Matter 9, 2603 (2013).
Node 9, Università di Roma La Sapienza (UNIROMA1)
The UNIROMA1-Node has been involved in a number of investigations related to patchy and associating colloids, whereupon the association between the same is caused either by tethered DNA-chains or by chemically patterned patches on their surfaces. In addition, the glassy dynamics of colloidal models has been investigated. A summary is presented below.
Experimental proof of the phase diagram of patchy particles. We have studied the experimental behavior of DNA stars with three or four sticky terminals, mimicking molecules with controlled limited valence. Solutions of such molecules exhibit a demixing curve with an upper critical point, whose temperature and concentration decrease with the valence .
Please see attached graphic
Fig. 17: The phase diagram of DNA-stars .
Gelling by heating. Exploiting the versatility of patchy interactions, we have investigated a system that forms a reversible gel upon heating . This is made possible by the use of a properly designed binary mixture of particles with valence four and two respectively and specific interactions. By means of molecular dynamics simulations it is observed that with increasing temperature the relaxation dynamics slows down by more than four orders of magnitude and then speeds up again. The system is thus a fluid both at high and at low temperatures and a solid-like disordered open network structure at intermediate temperature. Such phenomenon could be realized experimentally for example in a solution of DNA constructs of valence four in the presence of competing DNA single strands.
Phase Diagrams of One-Patch Colloids. In a systematic effort, we have investigated by computer simulations the phase diagram of one-patch colloids with different values of patch coverage at fixed attraction range (0.5 of the particle diameter). Going from the Janus case (50% coverage) to the hard sphere limit (0% coverage), a variety of different structures has been detected. On decreasing the coverage, particles self-assemble into clusters of different sizes and shapes, from micelles to one and two dimensional aggregates (tubes and lamellae) . For 30% of coverage, free-energy calculations show that the disordered tube phase, despite forming spontaneously from the fluid phase, is always metastable against a lamellar crystal. Also, a crystal of infinitely long packed tubes is thermodynamically stable, but only at high pressure . Keeping fixed the coverage (50%, corresponding to the Janus case) and decreasing the attraction range (from 0.5 to 0.2 of the particle diameter), we found stable crystalline structures with complicated bond-topologies on an underlying face-centered-cubic or hexagonal-close-packed lattice, as well as a phase consisting of wrinkled bilayer sheets, competing with both the fluid and the crystal phases . In all cases, a gas–liquid (colloidal-rich/colloidal-poor) phase separation does not occur (or it is metastable) because self-assembly into clusters which expose to their neighbors mostly repulsive surfaces suppresses phase separation and stabilizes cluster phases. This research effort involves the Ph.D-work of COMPLOIDS ESR Zdenek Preisler.
please see attached graphic
Fig. 18: Linear, planar, and irregular clusters formed by patchy particles with patches of 30% surface coverage .
Glassy Dynamics of the Square-Shoulder Potential. The second COMPLOIDS ESR of UNIROMA1, Gayatri Das has investigated the peculiar dynamics of square-shoulder system. Building on recent Mode Coupling Theory calculations, we have identified a complex scenario and different glassy states in this simple model of isotropic, repulsive potential. In particular, a disconnected glass-glass transition has been confirmed in simulations, with two endpoint singularities . In addition, more recent efforts with manuscripts in preparation have identified the presence of a higher-order singularity, the A4 point, with associated logarithmic dynamics and a novel invariant dynamics locus where state points have a dynamics that is indistinguishable at all time and length scales. Finally a crossover to a strong glass behavior is encountered in the limit where temperature goes to zero, giving rise to a crossover from a repulsion-driven fragile glass to a repulsion-driven strong glass.
Hard Spheres glasses: devitrification and polydispersity. In our collaboration with the UEDIN-Node, we are continuing to investigate the dynamics of hard spheres (HS). In the last year, we have focused mainly on two aspects. First, we have studied the devitrification (i.e. a glass-to-crystal transition) taking place in aged monodisperse hard sphere glasses and found that it is mediated by avalanche-like events, where a subset of particles undergo large rearrangements. An avalanche leads to an increase in the total crystallinity of the system, but most of the particles that become crystalline are not involved in the avalanche. The occurrence of avalanches is a largely stochastic process [E. Sanz et al., PNAS, under review 2013].
Second, we have studied the dynamics of polydisperse HS to provide an answer to an ongoing controversy in condensed matter physics: is there a glass transition in a collection of hard spheres below random close packing? Recent experiments have claimed that the glass transition in HS colloids at packing fraction 0.58 is pre-empted by `activated processes'. By simulating an experimentally-realistic system, we find that the dynamics is very sensitive to the shape of the particle size distribution (PSD), and not only to its normalized width (i.e. the polydispersity). The residual ergodicity observed beyond 0.58 is then the consequence of the presence of a tail in the PSD, leading to gradual, hierarchical arrest as packing fraction is increased [E. Zaccarelli et al., in preparation 2013].
1. S. Biffi, R. Cerbino, F. Bomboi, E. M. Paraboschi, R. Asselta, F. Sciortino, and T. Bellini, Proceedings of the National Academy of Sciences of the U.S.A. 110, 15633 (2013)
2. S. Roldan-Vargas, F. Smallenburg, W. Kob, and F. Sciortino, Scientific Reports 3, 2451 (2013).
3. G. Munao, Z. Preisler, T. Vissers, F. Smallenburg, and F. Sciortino, Soft Matter 9, 2652 (2013).
4. Z. Preisler, T. Vissers, F. Smallenburg, G. Munao, and F. Sciortino, Journal of Physical Chemistry B 117, 9540 (2013).
5. T. Vissers, Z. Preisler, F. Smallenburg, M. Dijkstra, and F. Sciortino, Journal of Chemical Physics 138, 164505 (2013),
6. G. Das, N. Gnan, F. Sciortino, and E. Zaccarelli, Journal of Chemical Physics 138, 134501 (2013).
Node 10, Foundation for Research and Technology Hellas (FORTH)
The FORTH-Node has been involved in Projects P8, P12, P16, P18, and P20. During the course of COMPLOIDS, FORTH has employed three ER’s, namely Dr. Domenico Truzzolillo, Dr. Laurence de Viguerie, and Dr. Frank Snijkers.
Project P8: Experimental investigations on the problem of the phase behavior of telechelic star polymers have started in coordination with the parallel simulation studies for UNIVIE and Prof. Panagiotopoulos. We have measured by SANS the form and structure of a series of phosphoro-zwitterionic telechilic 1,4-polyisoprene star polymers from the group of Prof. N. Hadjichristidis at the Univ. of Athens. The stars had different functionalities (f=3, 12) and arm molar mass (from 10 kg/mol to 50 kg/mol) . The data could not be fully quantified with the models by the COMPLOIDS-partners C. N. Likos (UNIVIE-Node) and A. Z. Panagiotopoulos (Princeton University, Associated Parnter) and we suspect that this relates to the fact that the true “dilute” regime for determining accurately the form factor was not reached. Nevertheless, the data were particularly useful in the qualitative sense at the effects of arm length and concentration were consistent with predictions.
Project P12: The work with the selected star block copolymer (a star whose arms are diblock copolymers of butadiene and styrene, the former being the inner part) with 64 and 80 arms and arm molar mass 30 kg/mol, the styrene having a composition of about 68%, has been completed . The systems showed tunability to solvent and temperature environments [3,4,5,6].
Project P16: The FORTH-node was involved in the development of a new light scattering technique for probing dynamics near solid surfaces. The Evanescent wave DLS (EWDLS) has been modified to boost the signal through the generation of the evanescent field by surface plasmon resonance in a metal thin layer on the top of the glass substrate. Besides the stronger signal allowing for probing of the rotational dynamics , REDLS offers surface monitoring and applications to biorelevant systems . In addition, single molecule Fluorescence correlation spectroscopy has been used to probe diffusion in well-designed confined media. The observed slowdown of the diffusion is a sensitive index of the confinement topology and the interactions with the surfaces of the medium. In collaboration with the UNIVIE-Node, a solid explanation of the experimental has been achieved .
Project P18: We have investigagted semifluorinated alkanes (SFA) at the air-water interface. Using a Langmuir trough we measured the surface pressure isotherms of such symmetric and asymmetric diblocks. We also carried out neutron reflectivity measurements at the PSI facility and complementary AFM measurements in films deposited on glass substrates at the Max-Planck Institute for Polymer Research, MPIP (group of H.-J. Butt). We confirmed the hierarchical ordering of these systems at the interface, forming surface micelles, which are then arranged in the form of two-dimensional jammed or percolated structure, depending on the molecular details . We have also studied the stability of the films and their rheology, which support and complement the structural studies . Further, we have completed a systematic study of colloidal monolayers (PMMA and PS latex particles) at the air-water interface. The particles were obtained from the group of K. Landfester in MPIP. We found that stable particle films and be formed and used a templates for ordering smaller particles . In addition, we have found that by varying the pH of the water subphase it is possible to tune the particle-particle interactions and hence move from multi-layer films with aggregates, to ordered films to nearly monolayers.
Project P20: We have considered the effects of added small linear homopolymer chains on the structure and dynamics of concentrated star-polymer solutions (ultrasoft mixtures), as well as those of added small hard-sphere-like particles to star glasses on the morphology of the mixtures. This project was carried out in close collaboration with the UNIVIE node, which provided theoretical guidance. The star/linear polymer studies have revealed that the addition of the linear chains exerts osmotic pressure that leads both to the shrinking and depletion of stars [12,13]. A particularly interesting finding is the fact that, as specific size ratios and volume fractions, upon increasing the fraction of added linear chains, the glass melts due to depletion, which further leads to a re-entrant arrested phase separation and star gelation . The consequences of this on nonlinear viscoelasticity of the mixtures have also been addressed . Furthermore, a consequence of osmotic forces in star/small linear mixtures is the shrinkage of stars combined with depletion; this leads to glass-to-liquid transition and a re-entrant gelation, instead of re-entrant (attractive) glass. More strikingly though, to so-obtained entropic gel melts upon heating, in contrast to what is known from hard-colloid/polymer mixtures; this is a consequence of the hybrid nature of the stars with a core being chemically different from the arms, which results in changing arm conformation upon heating, and hence gel melting. These important results, which open potentially new directions in the manipulation of soft colloids have been published recently .
For the unambiguous study of nonlinear rheological phenomena in such systems (such as properties beyond yielding, step shear rate measurements), it is imperative to avoid the many artifacts present. To this end we designed and developed a special home-made tool, partitioned cone-plate that ensures proper measurements. The tool has been tested with polymers in a range of temperatures and found to work well . We have applied this to the study of nonlinear shear in systems of polystyrene-grafted silica nanoparticles imbedded in polystyrene matrices, in collaboration with Prof. S. Kumar from Columbia Univ., USA. A manuscript detailing the key results, i.e that experimentally accessible shear is usually unable to overcome particle interactions and fully disperse nanoparticles, in currently under review. The work outlines the main phenomenological guidelines for yielding of nanoparticles network structures and links nicely to colloidal gels.
We have also explored experimentally the star/linear polymer systems in the limit of large polymers, and found that the stars act as effective confinements affecting the chain dynamics. This was an interesting side-project motivated by the above results and it will be complemented by theoretical analysis in the same collaborative fashion.
Finally, in a very fruitful collaboration with the UNIVIE-Node, the glassy dynamics of the star/hard-sphere system was examined in detail and from first principles. Systematic experiments by FORTH and first-principles theory coupled to simulations by UNIVIE have revealed a wealth of novel and interesting phenomena. Most remarkable is the morphological transition on adding hard spheres to a star glass, where a glass to liquid to re-entrant arrested phase separation has been found. We believe that this opens a new avenue for exploring the physics of out-of-equilibrium colloidal systems and clearly reflects the role of softness .
Please see attached graphics
Fig. 19: (a) The experimental state diagram of star-colloidal mixtures with size ratio ξ = 4 and star functionality f = 214. The vertical arrow denotes the star polymer density at which a star solution arrests in the experiment in the absence of colloids and the horizontal arrows denote the points where the system melts and revitrifies. (b) The MCT-phase diagram of the same system. The dashed line denotes the locus of points for which integral equations fail to converge due to a demixing phase transition, whereas the hand-drawn solid line separates the region of the liquid and the repulsive glass. From Ref. .
1. E. van Ruymbeke, D. Vlassopoulos, M. Mierzwa, T. Pakula, D. Charalabidis, M. Pitsikalis, and N. Hadjichristidis, Macromolecules 43, 4401 (2010).
2. J. Roovers, L.-L. Zhou, P. M. Toporowski, M. van der Zwan, H. Iatrou, and N. Hadjichristidis, Macromolecules 26, 4324 (1993).
3. D. Vlassopoulos and G. Fytas, Advances in Polymer Science 236, 1 (2010).
4. M. Kapnistos, D. Vlassopoulos, G. Fytas, K. Mortensen, G. Fleischer, and J. Roovers, Physical Review Letters 85, 4072 (2000).
5. E. Stiakakis, A. Wilk, J. Kohlbrecher, D. Vlassopoulos, and G. Petekidis, Physical Review E 81, 020402(R) (2010).
6. E. Zaccarelli, C. Valeriani, E. Sanz, W. C. K. Poon, M. E. Cates, and P. N. Pusey, Physical Review Letters 103, 135704 (2009).
7. M.Plum B.Menges G. Fytas, H.J. Butt, W. Steffen, Review of Scientific Instruments 82, 015102 (2011).
8. R. Raccis, A. Nikoubashman, M. Retsch, U. Jonas, K. Koynov, H.-J. Butt, C. N. Likos, and G. Fytas, ACS Nano 5, 4607 (2011).
9. L. de Viguerie, R. Keller, U. Jonas, R. Berger, C. G. Clark, Jr., K. Müllen, C. Klein, T. Geue, and D. Vlassopoulos, Langmuir 27, 8776 (2011).
10. C. O. Klein, L. de Viguerie, C. Christopoulou, U. Jonas, C. G. Clark, Jr., K. Müllen, and D. Vlassopoulos, Soft Matter 7, 7737 (2011).
11. N. Vogel, L. de Viguerie, U. Jonas, K. Landfester, C. K. Weiss, Advanced Functianal Materials 21, 3064 (2011).
12. A. Wilk, S. Huißmann, E. Stiakakis, J. Kohlbrecher, D. Vlassopoulos, C. N. Likos, J. K. G. Dhont, G. Petekidis, and R. Vavrin, European Physical Journal E 32, 127 (2010).
13. D. Truzzolillo, D. Vlassopoulos, and M. Gauthier, Macromolecules 44, 5043 (2011).
14. D. Truzzolillo, D. Vlassopoulos, and M. Gauthier, Journal of Non-Newtonian Fluid Mechanics 193, 11 (2013).
15. D. Truzzolillo, D. Vlassopoulos, M. Gauthier, and A. Munam, Soft Matter, 9, 9088-9093 (2013).
16. F. Snijkers, and D. Vlassopoulos, Journal of Rheology 55, 1167 (2011).
17. D. Truzzolillo, D. Marzi, J. Marakis, B. Capone, M. Camargo, A. Munam, F. Moingeon, M. Gauthier, C. N. Likos, and D. Vlassopoulos, Physical Review Letters 111, 208301 (2013).
Node 11, Schlumberger (SCR)
The SCR-node is involved in Project P21. A COMLOIDS-ER, Dr. Ankush Sengupta was hired and supervised instead by Dr Paul Hammond. Additional supervision was provided by Dr. Edo Boek, who was retained by SCR as a contractor, and by Prof. Daan Frenkel at the nearby UCAM Node. Initial evaluation of the problem and changes necessary to the lattice Boltzmann code to include surfactants revealed that the original proposal was too ambitious. The original objectives were therefore modified so that training and development of the foundations necessary for M1 became the focus. Dr Sengupta therefore learnt C programming, learnt sufficient hydrodynamics and learnt the lattice Boltzmann methodology. Detailed work was then undertaken to examine the boundary conditions necessary to study capillary flow.
The relative error in conductance calculations, for simulated flow of a single component single phase fluid through a capillary in three dimensions, by the Lattice Boltzmann (LB) method with bounce-back boundary conditions was studied. The relative error with respect to analytical results for capillary cross-sections of circular, triangular and square shapes were calculated as a function of the cross-section diameter, a, and for different alignment of the cross-section relative to the underlying lattice grid. It was shown that when the shapes are not aligned perfectly to the lattice, that the relative error decreases systematically with the size, a, as _ 1/a when a is evaluated by mapping the computed cross-sectional area, in terms of the enclosed number of grid points, to the respective geometrical shapes concerned. For perfectly aligned geometries, viz. the square capillary aligned to the LB lattice grid or rotated with its side along the diagonal of the LB grid, the relative error decreases as _ 1/a2. A simple method is suggested to locate the boundary wall depending on its orientation relative to the grid, such that the exact conductance of the new shape matches the LB computed conductance.
Node 12, Rhodia (RHOD)
The RHODIA-Node focused on the study of complex colloidal flow under shear. Investigations commenced with the development of experimental methods to measure simultaneously velocities, carrier velocities volume fractions of the colloids, in various geometries. Several experimental tools have been set up and are complementary.
The first experimental configuration consists in a channel flow. We have developed experimental procedures to track the trajectories of individual large particles using confocal microscopy in concentrated regimes. Key issues were to adapt and improve existing image processing algorithms to locate and track the colloids in the one hand, and to design well adapted microfluidic devices to avoid clogging in the other hand. Simultaneously, a procedure was developed to measure locally and simultaneously the volume fraction. This issue is important since the latter varies significantly under flow.
Second, a method based on fluorescence photobleaching under flow of small fluorescent dyes was developed to measure the velocity and the hydrodynamic dispersion of the carrier liquid. This method has been tested and validated with pure liquids in small channels , where only the mean velocity is measured. By using a vertical scan in wider channels and taking advantage again of confocal microscopy, we extended this method to measure velocity profiles [F. Schembri, H. Bodiguel, and A. Colin, in preparation]. The main novelty of this method rests on the fact that there is no tracer particles, but a molecular dye. Indeed, other tracer particles perturb the flow of the other ones.
A combination of these two methods has been achieved. Particles are immersed in a liquid colored with a fluorescent dye. The particle velocity, the particle volume fraction are measured through particle identification and tracking, and the local velocity of the suspending liquid is measured thanks to photobleaching velocimetry. We are thus able to determine velocity differences between the particles and the surrounding liquid, in the direction of the flow.
Finally, specific microfluidic devices were developed to study jet of colloids inside a Newtonian fluid. This geometry is of particular interest since it offers various degrees of freedom thanks to the control of both flow rates. It allows us to confine the flow, to produce elongational flows and modifies the boundary conditions. Considering industrial applications, such a configuration could allow the fabrications of fibers made of colloids, provided that the jet formation is stable.
The experiments have started by working on sample preparation and characterization. The main issue was to obtain a suspension with matched density and refractive index, which is furthermore fluorescent in order to be able to apply the methods described in the first part. We have succeeded in preparing such samples. They are made of PMMA particles in thioglycerol where some rhodamine is dissolved. The obtained suspensions are stable and we have been able to tune the colloids volume fraction up to 55%.
In order to better understand the role of colloids’ surface properties, emulsions made of highly viscous small droplets have been considered. The interest of this second system is coming from the fact that the droplets do not deform due to their very high viscosity similarly to solid particles, and given the small capillary numbers investigated but exhibit a perfectly smooth interface with the surrounding liquid, contrary to the PMMA particles which have a finite roughness. These emulsions consist of silicone oil dispersed in a water-glycerol mixture. The key issue of the preparation of this emulsion was to find the appropriate surfactant formulation be able to use the photobleaching velocimetry techniques that we have developed. Indeed, standard surfactants stabilize the fluorescent dye, which prevents its bleaching. We succeed in this issue by using solutions of NP10. However, contrary to the PMMA suspensions, only the refractive index could be matched accurately, the density of the silicone oil being lower than any aqueous solutions. We have also worked towards the reduction of the polydispersity of the droplets, and succeed in reducing it down to 20%.
After this important sample preparation issue, the experimental methods developed by the Node have been used with the two systems detailed above, in a concentration range between 5% to 50%, and with shear stress ranging between 0.1 and 10 Pa. Results in the simple channel geometry could be summarized with a few key observations.
First, focusing on particle volume fraction, we do observe for both emulsions of droplets and solid particles suspension a cross-stream migration towards the center of channel. In the case of the emulsion, buoyancy leads at small flow rates to a creaming, so that particles accumulate towards the upper wall. We thus observe a transition between a buoyancy-dominated regime to a shear stress-dominated one. The cross-stream migration at higher flow rates could be interpreted in the framework of shear-induced migration, which is known to occur in non-homogeneous flows. However, the physical reason for which migration occurs remains an open issue, and one of the usual hypothesis rely on the particle roughness. The fact that the non-deformable droplets also exhibit a similar cross-stream migration indicates that this argument is not relevant.
Second, the use of the simultaneous measurements of particle and suspending liquid velocity profiles reveals that there exists a velocity difference in the flow direction [F. Schembri et al., in preparation]. This relative velocity depends on the flow rates. It is negligible high flow rates, but up to of 20% of the mean velocity at lower velocities. The suspending liquid travels faster than the colloids in this regime.
Third, an important conclusion of our comparative study between the suspensions and the emulsion concern the long time stability of the flow. Flow of emulsions in straight channels remains perfectly steady in the range of concentration and flow rate studied. In contrast, a slowing down and eventually a clogging of the channel systematically appears when solid particles are used. This observation might be linked to the previous one, i.e. to particle accumulation due to migration in the flow direction. Since the main difference between the two systems concern their surface properties, this results may provide a nice way to avoid clogging by tuning the surface of the colloids.
Finally, experiments using the three-dimensional microfluidic device designed to form jets of colloids in a Newtonian fluid were conducted as well, focusing on the jet stability. Depending on the relative flow rates between the jet and the annular fluid, three regimes are evidenced. In the first one, the jet is stable and has a constant cross-section. In the two others the jet destabilizes either in small clusters of particles, either by a bending instability. The frontiers of these regimes have characterized experimentally as a function of the flow rates, the particle sizes and the viscosity of the suspending liquid.
please see the attached graphics
Fig. 20: Demonstration of the principle of the experimental method in straight channel. Left panel: scheme of the experiments and image of a bleached line which displacement is then tracked to achieve the measurement of the liquid velocity. Right panel: individual trajectories of the flowing particles.
please see attached graphic
Fig. 20: Concentration (bottom) and velocity profiles (top) of the emulsion system at two flow rates. In the velocity profile, the blue symbols correspond to the suspending liquid velocity while the white ones correspond to the particle velocity.
please see attached graphic
Fig. 21: Illustrations of the three regimes encountered in the jet geometry with PMMA particles in water. The arrows indicate the flow direction. The white line represents 200 mm. Top panel: stable jet. Middle panel: jet destabilizing in small clusters. Bottom panel: jet destabilized by a bending instability.
1. A. Cuenca and H. Bodiguel, Lab On A Chip 12, 1672 (2012).
2. A. Cuenca and H. Bodiguel, Physical Review Letters 108, 108304 (2013).
3. J. Beaumont , N. Louvet , T. Divoux , M-A Fardin , H. Bodiguel, S. Lerouge, S. Manneville, and A. Colin, Soft Matter 9, 735 (2013).
4. A. Cuenca, M. Chabert, M. Morvan and H. Bodiguel, Oil & Gas Science and Technology 67, 953 (2012).
5. L. Du, H. Bodiguel, C. Cottin, and A. Colin, Chemical Engineering Processes 68, 3 (2013).
6. H. Bodiguel and J. Leng, Chemical Engineering Processes 68, 60 (2013).
7. M. Romano, M. Chabert, A. Cuenca, H. Bodiguel, Physical Review E 84, 065302 (2011).
8. A. Colin, T. M. Squires, and L. Bocquet, Soft Matter 8, 10527 (2012).
9. M. Youssry, E. Lemaire, B. Caillard, A. Colin, and I. Dufour, Measurement Science and Technology 23, 125306 (2012).
10. P. Jop, V. Mansard, P. Chaudhuri, L. Bocquet, and A. Colin, Physical Review Letters 108, 148301 (2012).
11. O. Bonhomme, J. Leng, and A. Colin, Soft Matter 8, 10641 (2012).
12. V. Mansard and A. Colin, Soft Matter 8, 4025 (2012).
13. F. Carn, A. Colin, O. Pitois, and R. Backov, Soft Matter 8, 61 (2012).
14. P. Chaudhuri, V. Mansard, A. Colin, and L. Bocquet, Physical Review Letters 109, 036001 (2012).
Awards and Distinctions received by COMPLOIDS Principal Investigators and Associated Partners:
A number of prestigious awards, distinctions, and recognitions has been bestowed on COMPLOIDS Principal Investigators and Associates during the period 2009-2013, an achievement that confirms the high-standing of the involved scientists in the community. These distinctions are listed below in the order of the Nodes involved in COMPLOIDS.
1. Prof. Christos Likos (UNIVIE): Associate Editor of the Journal Soft Matter, 2011.
2. Prof. Christos Likos (UNIVIE): Fellow of the Royal Society of Chemistry, 2013.
3. Prof. Philip Camp (UEDIN): Journal of Chemical Physics Top 20 Reviewer, 2012
4. Prof. Philip Camp (UEDIN): Molecular Physics, Editorial Board Member, 2013
5. Prof. Philip Camp (UEDIN): American Physical Society Outstanding Referee, 2013
6. Prof. Philip Camp (UEDIN): Visiting Professor, Institute of Mathematics and Computer Science, Ural Federal University, Ekaterinburg, Russia, 2012, 2103
7. Prof. Mike Cates (UEDIN): Weissenberg Award of European Rheology Society, 2013
8. Prof. Mike Cates (UEDIN): Eli Burstein Lecturer, University of Pennsylvania, 2013
9. Prof. Mike Cates (UEDIN): Panel Members ERC Advanced Grant, 2013
10. Prof. Wilson Poon (UEDIN): Guest Professor, École Supèrieure de Physique et de Chimie Industrielles, Paris, Saint-Gobain Chair, February 2012
11. Prof. Wilson Poon (UEDIN): Universität Konstanz, University Senior Research Fellow, May 2012
12. Prof. Daan Frenkel (UCAM): 2013 Hinshelwood Lectures, Oxford University
13. Prof. Daan Frenkel (UCAM): 2012 Robert Scott Lecture, University of Californian at Los Angeles. 2013
14. Prof. Daan Frenkel (UCAM): Inducted as Elected Associate Fellow of TWAS – The World Academy of Sciences
15. Prof. Dimitris Vlassopoulos (FORTH): Society of Rheology Publication Award 2011
16. Prof. George Fytas (FORTH): Visiting Professor, University of Lille, France, July 2010
17. Prof. Randall Kamien (Upenn): Samsung Mid-Career Award, International Liquid Crystal Society, 2010
18. Prof. Randall Kamien (Upenn): Simons Investigator, 2013
19. Prof. Athanassios Z. Panagiotopoulos (Princeton U.): Member of the National Academy of Arts and Sciences of the U.S.A. 2012
20. Prof. Benjamin Rothenberg (Paris U.): - Prix jeune chercheur 2013 de la Division de Chimie Physique -- Young Researcher Prize from the joint division between the French Chemical and Physical Societies
21. Prof. Benjamin Rothenberg (Paris U.): Grand Prix Michel Gouilloud - Schlumberger de l’Académie des Sciences, 2013
Vienna, November 25, 2013
Christos Likos, ITN-COMPLOIDS Coordinator
Project Website: www.itn-comploids.eu
Christos N. Likos (ITN Coordinator)
Margret Pfeffer (Administration)
University of Vienna
Faculty of Physics
Grant agreement ID: 234810
1 November 2009
31 October 2013
€ 4 714 765
€ 4 714 765
Deliverables not available
Grant agreement ID: 234810
1 November 2009
31 October 2013
€ 4 714 765
€ 4 714 765
Grant agreement ID: 234810
1 November 2009
31 October 2013
€ 4 714 765
€ 4 714 765