(7hl) Modeling Liquid Crystals, Active Matter and Other Non-Equilibrium and Nonlinear Soft Materials | AIChE

(7hl) Modeling Liquid Crystals, Active Matter and Other Non-Equilibrium and Nonlinear Soft Materials


Zhang, R. - Presenter, University of Chicago
Research Interests:

Soft Matter comprises of a wide range of materials, which are deformable or structurally switchable by thermal or mechanical stress of the magnitude of thermal fluctuations. Because of the richness and complexity in its structures and properties, soft matter is promising for design of materials with novel features. Examples are liquid crystal-based biosensors, actuators, soft robotics, and kirigami-based mechanic metamaterials. Theory and modeling of soft matter are not only important for discovering functional material by design, but also helpful for understanding the biophysics of life, for instance, protein folding, cell morphogenesis, and animal flocking; This knowledge can be in return used to help design biomimetic, autonomous materials. The equilibrium structures of many soft matter can be predicted by free energy considerations. Their non-equilibrium behaviors and responses to driven forces, are however nonlinear and therefore difficult to model due to their intrinsic microstructures. I am interested in pursuing a career on modeling non-equilibrium and nonlinear soft matter, including but not limited to liquid crystal flows, active matter, and mechanic metamaterials.

Specifically, I propose to work in the following research directions as a faculty:

1) Liquid crystal flows. Liquid Crystals exhibit versatile mesophases, including nematic, smectic A, smectic C, columnar phases and their chiral counterparts. Nematic phase refers to a system when rod-like particles exhibit long-range orientational ordering but remain spatially disordered. The other mesophases encompass partial spatial ordering. These mesophases can engender distinct, periodic defect structures, for example blue phases and focal conic domains, which are useful for novel photonic devices and organizing and sorting microparticles and even surfactants. The above liquid crystal phases can be found in many dense suspensions of aspherical particles, such as carbon nanotubes, DNAs, virus, and certain drugs. Modeling their hydrodynamic behaviors could help us better understand the rheology of dense suspensions with emerging ordering. One could also use liquid crystals to transport cargos and separate particles. Therefore, a robust simulation technique on liquid crystal flows is beneficial. During my postdoc, I have developed a simulation tool for flowing nematics. I envision my future research direction to be modeling the flow of chiral nematics and other higher ordered liquid crystal mesophases.

2) Active Matter. Active matter converts other forms of energy into local mechanic work and drive the system out of equilibrium. Consequently, a spontaneous flow and structural ordering may emerge. Active matter can be biopolymer networks, bacteria suspensions, self-propelling colloids, and even vibrating rods. Active matter could be the candidate for biomimetic, autonomous materials. The major reason that hinders its wider and further applications is that it is very difficult to control and tailor the spontaneous flows. A special type of active matter is namely active nematics, which comprises of elongated particles and exhibit nematic phases. In such systems, topological defects may persistently move. If one is able to manipulate the motion of defects, one could transport defect-carried particles. As my second research direction, I plan to explore different active matters and find a uniform model to better elucidate their dynamics.

3) Mechanic Metamaterials. Elastic materials show linear response to small stresses. At higher stress, they may undergo buckling instabilities. This nonlinear behavior has been exploited to engineer mechanic metamaterials, which exhibit for example negative Poisson ratio. Another interesting direction for elastic materials is to design foldable three-dimensional structures out of two-dimensional materials. This simple, hierarchical material design philosophy could fundamentally advance our current manufacturing technique. However, the possible structures that lead to useful functions are not fully exploited. I plan to develop a robust simulation tool to handle buckling instabilities and able to predict the mechanic response of the structure under certain mechanic stresses.

During my Ph. D, I worked with Prof. Joel Koplik at Levich Institute in CCNY, on multi scale simulations of microfluidic phenomena. During my postdoc experience with Prof. Juan de Pablo at The University of Chicago, I developed a parallelized hybrid lattice Boltzmann code to simulate flowing nematic LC system, and applied it to the biopolymer systems to understand active nematics phenomena.

Teaching Interests:

(Computational) Fluid Mechanics; Thermodynamics; Statistical Physics; Transport phenomena; Liquid Crystals; Advanced Simulation Method for Soft Matter