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Hybrid Colloidal Systems with Designed Response

Periodic Reporting for period 2 - COLLDENSE (Hybrid Colloidal Systems with Designed Response)

Reporting period: 2017-01-01 to 2018-12-31

Colloids find different applications in almost every part of our lives -- medicine, food, cosmetics -- and so it might seem that these systems are fully understood and “tamed”. In reality, this is far from the case! Both fundamental understanding and a clear application strategy are still needed. Nowadays, soft and anisotropic colloids are in high demand, not only due to their rich phase behaviour, but also due to the possibility to control them with various external drives. The main aim of COLLDENSE was to elucidate the relationship between "shape/internal structure/deformability of a single colloid"-"density of the hybrid colloidal system"-"external drive (shear, field, pH)" and the “macroscopic response/phase behaviour of these systems”. The scientific part of COLLDENSE was divided into three scientific workpackages (WPs), according to the hierarchical complexity of the building blocks. The main objective of the WP1 was to understand the behaviour of soft colloids (star polymers, micelles, droplets) in the equilibrium conditions and under mechanical, electric and rheological drives. WP2 was dedicated to the study of hybrid colloids (telechelic stars, dipolar colloids, functionalized droplets). Finally, in WP3, we studied mixtures of various colloids from WP1 and WP2. This combination allowed us to obtain broad knowledge of mechanical and rheological properties of colloidal systems, while simultaneously being able to trace back the dependence on the complexity of building blocks through comparing results obtained in different WPs.
In WP1 of COLLDENSE we had 5 specific projects, encompassing synthesis, experimental analysis, simulations and theoretical modelling of the properties of deformable colloids under external drive. We started with single droplets, using optical microscopy describe their pair interaction. It turned out that the composition of droplets is a key parameter to tune in order to change their behaviour. Another project that studied in computer simulations the mobility of a single 3D droplet depending on its composition and the properties of the solvent, showed that the transition from the osmosis to the electrophoresis could be found changing the solvation energy of the droplet. The ensemble of droplets has been also addressed in the simulations of the 3rd project, where the soft-hard transition in a 2D system was found and the discontinuous shear thinning was discovered. The effects of shear have been also studied by the 4th project experimentally. It showed that dense star polymers in melt could exhibit the properties of both polymers and colloids, namely they form a soft solid above the glass temperature, leading to a practical jamming of the system. Finally, to elucidate the mechanical properties and the phase diagram, a new theoretical approach (5th project) has been developed.

In WP2 we investigated hybrid colloids: DNA coated droplets, functionalized micelles, micro gels, telechelic star polymers and dipolar colloids. In the 1st project, using optical tweezers and microscopy, DNA coated droplets were synthesized, whose interactions can be tuned by light. It was shown that the rheological behaviour of the functionalized telechelic stars can be controlled by changing their topology. For that, in the 2nd project, a special molecular dynamics method was developed. Experimentally, in the 3rd project special micelles and microgels were synthesized with tuneable isotropic attractive interaction. Extensive comparison of the rheology and relaxation of the gels made of these hybrid colloids to those made of simple particles were studied. In simulations, relaxations of these systems were addressed in the 4th project of WP2. It was shown that shear can change their behaviour from percolation to phase separation. Talking about percolations and phase transitions in hybrid colloids is impossible without having a stable method to calculate cluster partition functions. This method has been developed in the frame-work of the 5th project in WP2 and tested for hybrid dipolar colloids.

One of the most versatile and efficient strategies for designing new materials with unconventional behaviour is based on competitive interactions. This was the part of COLLDENSE (WP3), in which we studied mixtures of complex colloids. The first project in WP3 was studying the mixture of two population of colloids, and as a result, gels with controllable strength were constructed. Such mixtures prove to have a large potential for industrial applications. The 2nd industrial project is dedicated to the study of self-filtration and jamming in gels. It has been shown that the rheology of these systems can be controlled by tuning the process of gel drying under different conditions and confinements. Rheological measurements were also the subject of the 3rd project. Here, however, the mixture of various grafted anisotropic nanoparticles were investigated. It turned out that soft rods are the most promising candidates to show the richest phase diagram. The last two projects addressed the study of DNA gels. The purpose of one of them was to develop a simulation hybrid Monte Carlo method for DNA origami. The method was developed and tested. In the second one, the experimental synthesis and light/neutron scattering characterization of DNA stars was performed. These stars turned out to be the first known system to form a gel if heated and melt if cooled down.

Along with the fundamental scientific value that all the results obtained within the project possess, the outcome will be used as a guideline for synthesis of new smart colloid-based materials with a fine-tuneable properties and responses, such as foods, cosmetics, industrial and domestic chemistry products.
The ESRs of Colldense were given a unique opportunity to perform research in a highly active, interdisciplinary and inter-sectorial environment. As a result, more than 90 scientific papers and one book were published during four years. All of them are now available to broad audience due to the open access policy. More than 90 presentations were delivered at more than 40 international scientific events. Our ESRs were trained in applying and developing state-of-the-art theoretical, numerical, and experimental techniques to tackle problems in the fabrication of new colloidal materials. The exposure to the non-academic sector, assured by specifically targeted industrial training, allowed ESRs to gain experience in the interplay between academic and industrial research. The organisation of science for refuges workshops, public lectures, scientific exhibitions and educative workshops (more than 20 events) offered benefits toward the public understanding of science, while at the same time sharpening the skills of the ESR’s in putting forward convincingly the relevance of their research work. We are proud that approximately half of the ESRs decided to continue academic careers: one of them already found a PostDoc position in the US, another in Italy. Among those ESRs, who decided to change for industry, 4 found jobs in prestigious companies as L'Oreal, PTV, OKRA Technologies. All these efforts of COLLDENSE ESRs and PIs, we believe, enhanced the position of the EU in the field of soft matter research and prepared 15 highly qualified, mobile, solution-oriented young specialists able to think out of the box and contribute to both Industrial and Academic environment.
Final Meeting, ESRs of COLLDENSE