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Full-scale COmputational design of Porous mesoscale MATerials

Periodic Reporting for period 3 - COPMAT (Full-scale COmputational design of Porous mesoscale MATerials)

Reporting period: 2019-10-01 to 2021-03-31

The main problem/issue addressed by COPMAT is the computational design of new families of soft mesoscale materials (SMM) for a variety of applications in material science, engineering and bio-medicine. Examples include, among others, the production of scaffolds for the growth of cell tissues for regenerative medicine, new porous materials for catalysis and energy applications, as well as food processing and pharmaceuticals.

SMM are based on new, hybrid, states of matter resulting from the combination of the three fundamental ones: Gas, Liquid and Solid. Typical examples are emulsions (liquid-liquid, say water-oil), foams (liquid-gas, say water-air), jels (liquid-solid, say water-silica) and aerosols (gas-solid), to name but a few among the most important ones.

A tantalising property of such hybrid states of matter is that, due to various forms of non-linearity and non-locality, their mechanical and rheological behaviour, e.g. how they deform and move under the effect of external loads, cannot be traced back to the behaviour of the basic states they are made of. For instance, under common conditions, both air and water respond in linear proportion to the external loads (Newtonian fluids) but foams definitely don't. It is precisely this nonlinear emergent behaviour which confers to SMM completely novel properties, hence new applications.

For instance, one of the most distinctive property of SMM is their ability to assemble into supramolecular structures, such as bubbles or droplets, which serve as effective building blocks of the material. In a metaphorical language, one could say that SMM are made of droplets and bubbles rather than molecules. Of course, droplets and bubbles cannot replace molecules in full for many reasons, lack of chemical specificity in the first place; however they show a rich variety of assembly capabilities which open up
unique prospects for large-scale material design, which would not be possible for molecular-based materials.

The above picture speaks clearly for the industrial and societal importance of the problem, which is hard to overstate: energy, environment, health, all may draw major benefits from the industrial application of soft mesoscale materials.

No less important, though, is the interest for fundamental science, most notably non-equilibrium thermodynamics, soft matter and biology.

The reason is that the rheology and the thermo-mechanical properties of the SMM at the scale of experimental interest (mm to cm) depend crucially on the effective
interactions between these supramolecular structures, particularly when their mutual interfaces come in near-touch, which occurs at the scale of
a few nanometers. This involves the concurrent nonlinear interactions at scales spanning from a few nanometers all the way up to the scale of the device, i.e.
millimeters and above, thereby raising a very demanding multiscale challenge to both theory and simulation.

Innovative computational solutions to such a multiscale challenge lie at the hard-core of COPMAT.

Besides leading-edge research, this also has an important educational value, since the outstanding challenges of modern science and society are
invariably characterised by the need of formulating multiscale models and computational tools capable of simulating complex phenomena across multiple scales.

The overall objective of COPMAT is therefore to develop a new family of computational techniques capable to assist, guide and possibly anticipate the design of
porous mesoscale materials, starting from nanoscale interactions all the way up to the size of the device. Such computational techniques are then used to simulate with microfluidic devices of assorted types, such as flow focusers, step emulsifiers and others.

This is pursued following a multifold computational strategy, based on an optimal combination of three main modelling routes:

1) Coarse-grained Lattice Boltzmann (LB) models
2) Multigrid LB
3) Combination of LB with Discrete Particle (DP) methods.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far.

As of this report, May 2020, we have performed substantial work across all five COPMAT WP's, namely:

WP1) Microscopic foundations of soft glass rheology

WP2) Computational design of multijel materials

WP3) Computational design of trabecular porous media

WP4) Computational design of soft mesoscale molecules

WP5) Dissemination, Communication and Exploitation activities

In more detail:

We have studied the rheology of dense emulsions under different regimes, including the effects of nano-corrugated walls in microchannels. On the methodological side, we have developed a new coarse-grained LB model (Regularized Color Gradient with Near-Contact Interactions), initiated the implementation of multigrid-refinement and also developed original hybrid methods based on the combination between LB and DP methods [See BIB_WP1, BIB_WP2].

We have developed a new parallel code (LBsoft) from scratch, to simulate the dynamics of bijels with dispersed colloids and tested its parallel performances.
We are currently in the process of exploiting LBsoft to study the rheology of confined bijels under shear in order to produce highly directional (anisotropic) mesoscale materials [See BIB_WP2].

We have performed an extensive series of numerical simulations aimed at understanding the basic mechanisms which control the formation of droplets from oil jets in
flow-focuser microfluidic devices. We have also studied the effect of the design parameters (ratio of dispersed/continuum mass flows, geometrical parameters of the microchannel) on the spatial structure of the resulting droplet configuration (soft flowing crystals), which is a piece of crucial information for the industrial design of trabecular porous media out of microfluidic experiments [see BIB_WP1, BIB_WP3].

We have explored the dynamics of small droplets (cores) contained in larger droplets (bag) transported by a carrier fluid within a microchannel flow. This study has revealed a rich variety of novel non-equilibrium states which open new perspectives both for the design of new materials based on hierarchal micro-emulsions (droplets within droplets), as well as for drug-delivery purposes [See BIB_WP4].

We have presented our work in several international conferences, as well as dissemination events, including the publication in broad-audience magazines and education initiatives for high school teachers and students [BIB_WP5]. We also plan to apply for a PoC (Proof of Concept) action, to embed the Color Gradient scheme within a commercial code to transfer the COPMAT technology to the microfluidic market.
I am pretty satisfied with the progress achieved so far, which went in many respects beyond my own (high) expectations.

1) To begin with, the coarse grained Lattice Boltzmann scheme has proved very successful in describing a number highly complex rheological conditions with substantial near-contact interactions between the droplets. In particular, it has proved capable of quantitatively predicting the behaviour of flow focusers, stop emulsifiers and lately also microfluidic crystals.

This represents a major breakthrough in the LB methodology, as no pre-existing LB model would be able to describe the interaction of complex interfaces once they come in near-touch (a few nanometers). Standard LB models would lead to a coalescence (a disaster for the design of the material) or unphysical interactions due to the lattice discreteness (spurious currents), which impair the fidelity of the simulations.

In fact, to the best of our knowledge, this scheme is the only one capable of simulating not only the structure of soft flowing crystals within a microfluidic device but also the formation of droplets in such devices. The latter is a very complex phenomenon, involving jet breakup, and poses a significant challenge to any simulation method.

This success points strongly to the existence of a basic scale separation between the phenomena which control the near-contact interactions between the interfaces and the overall rheology.

In other words, once coalescence is staved off, the mechanisms which control the interfacial repulsion do not seem to need a realistic microscopic
description, namely, they exhibit sufficient universality to allow a coarse-grained representation. This is a major result in two respects: first, it highlights the existence of universal mechanisms in soft flowing matter (a mechanism which we called Extended Universality), second, it enables a very efficient simulation tool for the design of soft mesoscale materials.

2) A second item where COPMAT went beyond the state of the art the development of hybrid Lattice-Boltzmann-Mesoscale particle models for the description of complex fluid flows. Although we are not yet to the point of simulating realistic microfluidic devices, the merge between the above techniques is decidedly new, hence beyond the pre-existing state of the art, as witnessed by excellent referee reports and swift publication.

3) Finally, the third item is the HPC code LBsoft. Although the computational model itself is largely based on existing models of fluid-particle interactions (with original details in the time marching scheme, though), the HPC implementation is. Indeed, we have produced the first open-source version, with a very transparent and detailed discussion of the many computational/programming challenges that need to be faced to achieve satisfactory parallel performance.

These highly-technical details are key for third-parties users, which may wish to simulate bijels and related materials without going through the very time-consuming ordeal of developing their own code.

Given the wide arrays of tools that have been developed within the first half of COPMAT, we plan to exploit them to explore novel/exotic states of soft flowing matter and explore their suitability to the design of new soft mesoscale materials.

In particular, we expect innovative insights and results with concern to the following new materials:
i) Microfluidic crystals, ii) Multiple-emulsions, iii) Confined bijels.

For microfluidic crystals, we plan to study and identify the optimal operational parameters for microfluidic experiments aimed at producing the most suitable droplet clusters serving as building blocks (motifs) for new materials. Among others, it would be interesting to understand whether, besides droplet crystals, we may also control the formation and production of amorphous states such as "droplet glasses".

For multiple-emulsions, we expect to offer guidance and inspiration to a novel generation of microfluidic experiments aiming at generating soft hierarchical materials (droplets within droplets).

Prospective applications may be envisaged in biomedical, pharmaceutical and food-processing design, although exploring these aspects in full depth will certainly
command tight contacts with industrial partners (the IIT has dedicated offices to this purpose, which we plan to get in touch with in the 2H of the project).

Besides applications, the idea of investigating "Dropland", the land where materials are made of droplets instead of molecules, is fascinating on its own right, as a fundamental the problem of non-equilibrium thermodynamics with many applications in material science.

As to bijels, we expect to perform a systematic study of their rheology under confinement, a difficult and highly demanding computational task. Indeed, preliminary simulations indicate that the stability of bijels under shear is highly sensitive to the fluid-solid and solid-solid nanoscale interactions.

We also expect to complete the multigrid version of LBsoft. In light of the major success of the coarse-grained LB, this task has now less priority than we thought in the beginning but shall try to complete it anyway.

Finally, in the 2H of COPMAT, we wish to understand whether and to what extent the main COPMAT goals can benefit from the resort to Machine Learning.
We foresee potential breakthroughs in the automated search and formulation of optimal coarse-grained models, but this is entirely open at the time of this writing.


>>> BIB_WP1

WP1.1) Lin C., Luo K.H. Fei L., Succi S., A multi-component discrete Boltzmann model for nonequilibrium reactive flows, Scientific Reports, vol. 7, (no. 1), 2017, 10.1038/s41598-017-14824-9

WP1.2) Fei L., Scagliarini A., Montessori A., Lauricella M., Succi S., Luo K.H. Mesoscopic model for soft flowing systems with tunable viscosity ratio, Physical Review Fluids, vol. 3, (no. 10), 2018, 10.1103/PhysRevFluids.3.104304

WP1.3) Zhang Y., Xu A., Zhang G., Gan Y., Chen Z., Succi S., Entropy production in thermal phase separation: A kinetic-theory approach, Soft Matter, vol. 15, (no. 10), pp. 2245-2259, 2019, 10.1039/c8sm02637h

WP1.4) Fei L., Du J., Luo K.H. Succi S., Lauricella M., Montessori A., Wang Q., Modeling realistic multiphase flows using a non-orthogonal multiple-relaxation-time lattice Boltzmann method, Physics of Fluids, vol. 31, (no. 4), 2019, 10.1063/1.5087266

WP1.5) Pelusi F., Sbragaglia M., Scagliarini A., Lulli M., Bernaschi M., Succi S., On the impact of controlled wall roughness shape on the flow of a soft material, Europhysics Letters, vol. 127, (no. 3), 2019, 10.1209/0295-5075/127/34005

WP1.6) A. Montessori, A. Tiribocchi, F. Bonaccorso, M. Lauricella, S. Succi,
Lattice Boltzmann simulations capture the multiscale physics of soft flowing crystals,
in press on Phil. Trans. Roy. Soc. A.

WP1.7) Tiribocchi A., Montessori A., Miliani S., Lauricella M., La Rocca M., Succi S., Microvorticity fluctuations affect the structure of thin fluid films, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, vol. 100, (no. 4), 2019, 10.1103/PhysRevE.100.042606

WP1.8) Montessori A., Lauricella M., Succi S., Mesoscale modelling of soft flowing crystals, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 377, (no. 2142), 2019, 10.1098/rsta.2018.0149

WP1.9) L Fei, A Scagliarini, KH Luo, S Succi, Discrete fluidization of dense monodisperse
emulsions in neutral wetting microchannels, Soft Matter 16, 651 2020.

WP1.10) A. Montessori, M. Lauricella, N. Tirelli, S. Succi, Mesoscale modelling of near-contact interactions for complex flowing interfaces, Journ. Fluid. Mech. 872, 327 (2019).

WP1.11) M. Lauricella, S. Melchionna, A. Montessori, D. Pisignano, G. Pontrelli, S. Succi, Entropic lattice Boltzmann model for charged leaky dielectric multiphase fluids in electrified jets, Phys. Rev. E. 97, 033308 (2018).

WP1.12) S. Succi, M. Lauricella, Lattice propagators and Haldane-Wu fractional statistics, EuroPhys. Lett. 122, 1 (2018).

WPI.13) G. Di Ilio, D. Chiappini, S. Ubertini, G. Bella, S. Succi, Fluid flow around NACA 0012 airfoil at low-Reynolds numbers with hybrid lattice Boltzmann method, Computers & Fluids 166, 200-208 (2018).

WPI.14) S. Succi, Of Naturanless and Complexity, Eur. Phys. J. Plus 134, 97 (2019).

WPI.15) A. Gabbana, M. Polini, S. Succi, R. Tripiccione, and F. M. D. Pellegrino, Prospects for the Detection of Electronic Preturbulence in Graphene, Phys. Rev. Lett. 121, 236602 (2018).

WP1.16) G. Di Ilio, D. Chiappini, S. Ubertini, G. Bella, S. Succi, A moving-grid approach for fluid–structure interaction problems with hybrid lattice Boltzmann method, Comp. Phys. Comm 234, 137-145 (2019).

WPI.17) A. Gabbana, D. Simeoni, S. Succi, and R. Tripiccione, Relativistic dissipation obeys Chapman-Enskog asymptotics: Analytical and numerical evidence as a basis for accurate kinetic simulations, Phys. Rev. E 99, 052126 (2019).

WPI.18) K. Flouris, S. Succi, H. J. Herrmann, Quantized Alternate Current on Curved Graphene, Condens. Matter 4, 39 (2019).

>>>> BIB_WP2

WP2.1) Tiribocchi A., Bonaccorso F., Lauricella M., Melchionna S., Montessori A., Succi S., Curvature dynamics and long-range effects on fluid-fluid interfaces with colloids, Soft Matter, vol. 15, (no. 13), pp. 2848-2862, 2019, 10.1039/c8sm02396d

WP2.2) Tiribocchi A., Lauricella M., Montessori A., Melchionna S., Succi S., Disordered interfaces in soft fluids with suspended colloids, International Journal of Modern Physics C, vol. 30, (no. 10), 2019, 10.1142/S0129183119410043

WP2.3) Succi S., Amati G., Bernaschi M., Falcucci G., Lauricella M., Montessori A., Towards Exascale Lattice Boltzmann computing, Computers and Fluids, vol. 181, pp. 107-115, 2019, 10.1016/j.compfluid.2019.01.005

WP2.4) Bernaschi M., Melchionna S., Succi S., Mesoscopic simulations at the physics-chemistry-biology interface, Reviews of Modern Physics, vol. 91, (no. 2), 2019, 10.1103/RevModPhys.91.025004

WP2.5) S. Succi, G. Amati, F. Bonaccorso, M. Lauricella, A. Montessori, A. Tiribocchi,
Towards exascale design of soft mesoscale materials, submitted.

WP2.6) M. Lauricella, F. Bonaccorso, A. Montessori, A. Tiribocchi, G. Amati, M. Bernaschi, S. Succi,
LBsoft: a parallel open-source software for simulation of colloidal systems, submitted,

WP2.7) A. Montessori, A. Tiribocchi, M. Lauricella, S. Succi, A Coupled Lattice Boltzmann-Multiparticle collision method for multi-resolution hydrodynamics, in press on Journal of Computational Science.

WP2.8) A. Montessori, M. Lauricella, A. Tiribocchi, F. Bonaccorso, S. Succi, Multiparticle collision dynamics for fluid interfaces with near-contact interactions, in press on Journal of Chemical Physics.

>>>> BIB_WP3

WP3.1) Basagaoglu H., Harwell J.R. Nguyen H., Succi S., Enhanced computational performance of the lattice Boltzmann model for simulating micron- and submicron-size particle flows and non-Newtonian fluid flows, Computer Physics Communications, vol. 213, pp. 64-71, 2017, 10.1016/j.cpc.2016.12.008

WP3.2) Montessori A., Lauricella M., Succi S., Stolovicki E., Weitz D., Elucidating the mechanism of step emulsification, Physical Review Fluids, vol. 7, (no. 3), 2018, 10.1103/PhysRevFluids.3.072202

WP3.3) Basagaoglu H., Succi S., Wyrick D., Blount J., Particle Shape Influences Settling and Sorting Behavior in Microfluidic Domains, Scientific Reports, vol. 8, (no. 1), 2018, 10.1038/s41598-018-26786-7

WP3.4) Montessori A., Lauricella M., La Rocca M., Succi S., Stolovicki E., Ziblat R., Weitz D., Regularized lattice Boltzmann multicomponent models for low capillary and Reynolds microfluidics flows, Computers and Fluids, vol. 167, pp. 33-39, 2018, 10.1016/j.compfluid.2018.02.029

WP3.5) Basagaoglu H., Blount J., Succi S., Freitas C.J. Combined effects of fluid type and particle shape on particles flow in microfluidic platforms, Microfluidics and Nanofluidics, vol. 23, (no. 7), 2019, 10.1007/s10404-019-2251-9

WP3.6) Montessori A., Lauricella M., Tiribocchi A., Succi S., Modeling pattern formation in soft flowing crystals, Physical Review Fluids, vol. 4, (no. 7), 2019, 10.1103/PhysRevFluids.4.072201

WP3.7) A Montessori, A Tiribocchi, M Lauricella, F Bonaccorso, S Succi,
A Multiresolution Mesoscale Approach for Microscale Hydrodynamics,
Advanced Theory and Simulations, 1900250, 2020

WP3.8): Marco Lauricella, Sauro Succi, Eyal Zussman, Dario Pisignano, and Alexander L. Yarin
Models of polymer solutions in electrified jets and solution blowing
Rev. Mod. Phys., Accepted, 22 April 2020

WP3.9) A. Montessori, M. Lauricella, E. Stolovicki, D. A. Weitz, S. Succi, Jetting to dripping transition: Critical aspect ratio in step emulsifiers, Phys. of Fluids 31, 021703 (2019).

WP3.10) M. Meere, G. Pontrelli, S. McGinty. "Modelling phase separation in amorphous solid dispersions.", Acta biomaterialia 94, 410-424 (2019).

>>> BIB_WP4

WP4.1) Succi S., Montessori A., Falcucci G., Dynamic symmetry-breaking in mutually annihilating fluids with selective interfaces, Journal of Statistical Mechanics: Theory and Experiment, vol. 2019, (no. 8), 2019, 10.1088/1742-5468/ab3459

WP4.2) G. Negro, L. N. Carenza, A. Lamura, A. Tiribocchi, G. Gonnella, Rheology of active polar emulsions: from linear to unidirectional and inviscid flow, and intermittent viscosity, Soft Matter 15, 8251-8265 (2019).

WP4.3) A Tiribocchi, A Montessori, S Aime, M Milani, M Lauricella, S Succi, D. Weitz,
Novel nonequilibrium steady states in multiple emulsions, Physics of Fluids 32 (1), 017102 (2020).

WP4.4) E. Carr, G. Pontrelli, Drug delivery from microcapsules: How can we estimate the release time?, Math. BioSci 315, 108216 (2019).

WP4.5) A. Tiribocchi, A. Montessori, M. Lauricella, F. Bonaccorso, S. Succi, S. Aime, M. Milani, D. Weitz,
The vortex-driven dance of droplets within droplets, submitted

>>> BIB_WP5

WP5.1) S. Succi, F. Bonaccorso, M. Lauricella, A. Montessori, A. Tiribocchi,
When the physics of micro fluids becomes an art, Platinum, p. 95, July 2019

WP5.2) S. Succi, Nell'Universo parallelo dei fluidi, La Stampa, Nov 6, 2019