From Topology to Morphology: Defects, Shape Evolution, and Auto-origami in Soft Matter
We explore novel mechanisms of pattern formation in soft matter, examining why a lipid membrane crumples during a phase transition and how stimuli-responsive liquid crystal polymer films can be patterned to induce programmed shape transformations . In both of these materials, whose constituent molecules align to form orientationally ordered phases, topological defects play a key role: they drive changes in morphology by inducing curvature. In lipid membranes cooled through a phase transition into the tilted “gel” phase, we theorize that defects nucleate spontaneously and then coarsen via kinetic competition between defect pair-annihilation and membrane shape evolution. We explore this process via simulation using a coarse-grained model and also study membranes with nematic order. Next we examine the role of defects in stimuli-responsive liquid crystal polymers, which flex when exposed to light or a change of temperature. If a precise pattern of defects is induced in the sample when it is cross-linked, a process known as “blueprinting,” then under stimulus an initially flat film will twist, curl, or fold into a complex shape, a form of programmed auto-origami. We use 3-d nonlinear finite element simulation studies to explore the mechanism by which the complete trajectory of motion is encoded in the sample’s nematic director field, and compare with relevant experiments.
תאריך עדכון אחרון : 29/04/2015