Programmable and Emergent Structures in Soft Matter: Chirality, Polarity, and Auto-Origami

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Non-technical Summary:This award provides support for theoretical studies of responsive liquid crystal polymers, a form of plastic that spontaneously changes shape under heating or cooling. Rod-shaped liquid crystal molecules bonded to the polymer's main chains are disordered in orientation at high temperature but align at low temperature, inducing the polymer chains to extend in a parallel direction, and as a result the material stretches when cooled. Some materials containing light-sensitive dyes also change shape in response to illumination. A sample prepared with a non-uniform imposed pattern of local molecular orientation, a process known as blueprinting, shows complex shape evolution as the induced stress/strain is not uniform. The blueprinted pattern thus encodes a complex trajectory of movement from an initial state, e.g. a flat thin film, to a final state that is folded, curved, or twisted, a form of programmed auto-origami. Computer simulation studies of this process will explore the mathematical relationship between blueprinted structures and the resulting shape change. These materials have potential application in robotics, light-driven mechanical devices, touch displays, biomedical devices, and switchable surface textures. Related studies will examine shape change, pattern formation, and phase behavior in lipid membranes and liquid crystals. Outreach efforts, including research internships for 60+ high school students and annual science fair for six school districts, attract students to STEM careers and aim to improve the diversity of the STEM workforce.Technical Summary:This award supports theoretical/computational research and education in soft matter physics. It combines computer simulation and fundamental theory to investigate mechanisms of microstructural/shape evolution and pattern formation in soft matter. The proposed theory/modeling studies of orientationally ordered lipid membranes and nematic solids are united by themes of differential geometry, curvature, topological defects, complex ordering and response, topology, and self-assembly. The principal problems to be investigated are: (1) Auto-origami: nematic solids as programmable, stimuli-responsive materials; (2) Lipid membranes: coupling of topological defects and curvature; (3) Phase transitions in liquid-crystal elastomers: kinetic evolution of polydomain structures; (4) Flexoelectricity in liquid crystals: formation of complex modulated phases. In all of these cases, the PI's will collaborate with experimental scientists to compare predictions with experiments on physical and biological systems.This research is connected to fundamental problems in self-assembly, nonlinear elasticity, topological defects, and differential geometry. Potential applications of outcome of this research could include soft actuators, shape control of lipid vesicles for drug delivery, self-assembly of vesicles for photonic crystals, and new liquid-crystal display technologies and switchable surface textures.