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Controlled Transport and Assembly of Soft Complex Matter

Subject Area Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
Experimental and Theoretical Physics of Polymers
Synthesis and Properties of Functional Materials
Fluid Mechanics
Term from 2015 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 274340645
 
Final Report Year 2022

Final Report Abstract

The overarching goal of this project was to study the controlled transport and assembly of soft materials through external stimuli. We developed theoretical models and computer simulations to elucidate how soft systems can be driven into equilibrium or long-lived metastable states that would otherwise be inaccessible. Further, we explored how the microscopic properties and interactions of the constituent particles influence the resulting macroscopic material properties, and how such relations can be engineered to fabricate tailored materials. The research was conducted in close partnership with experimental groups, which immensely helped to accelerate, cross-validate, and inspire the research process. For example, we demonstrated how microfluidic devices can be utilized to separate mixtures of polymers based on their size, rigidity, and topology. Further, we studied the flow-induced self-assembly of Janus colloids, i.e., amphiphilic particles with one hydrophilic and one hydrophobic hemisphere, finding growth of the self-assembled micelles under moderate shear before breaking up at high shear rates. We also explored the directed assembly of polymeric nanoparticles driven by rapid solvent exchange, a simple technique suitable for large scale fabrication of internally structured particles. We revealed the underlying molecular mechanisms of nanoparticle formation and developed design strategies for fabricating amphiphilic Janus particles, which were then verified through complementary experiments. In the past few years, my group has also studied the evaporation of colloidal dispersions, which is an inherently non-equilibrium process relevant for many applications, such as coating, printing, and spray drying. For quickly drying bidisperse colloidal mixtures, we discovered spatial segregation of the two particle species, with the smaller ones accumulating at the liquid-air interface followed by a homogeneously mixed region of small and big colloids. This drying-induced phase separation was also observed experimentally, and we rationalized this counter-intuitive behavior through a multicomponent diffusion model. Finally, we studied the structure and material properties of polymer grafted nanoparticles, effectively one-component hybrid materials that combine the properties of hard (inorganic) nanoparticles and soft (organic) polymers. In close collaboration with experimentalists, we investigated the relation between the microstructure and the elastic moduli of these composite materials, finding that the strong overlap and interpenetration of sparsely grafted brushes increased the elastic and shear moduli by up to 30% compared to dense brush materials with shorter grafts at the same NP loading. Further, we found that these materials are auspicious materials for gas separation applications with high selectivity and permeability. To facilitate this research, we developed and implemented various multiscale simulation methods, which are publicly available. For example, we co-developed a new technique for the computation of neighbor lists based on binary search trees, and devised artificial neural networks for predicting effective pair potentials and equations of state. All in all, the research conducted within this project drastically improved our understanding of fundamental non-linear physics on the mesoscale, and led to novel techniques for the controlled manipulation and fabrication of soft matter.

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