From Topology to Morphology: Defects, Shape Evolution, and Auto-origami in Soft Matter

Image details on Prof. Selinger's webpage

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 [1] and also study membranes with nematic order [2]. 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 [3].

Work supported by NSF-DMR 1106014, NSF-DMR-1409658, and NSF-CMMI 1436565.
[1] LS Hirst, A Ossowski, M Fraser, J Geng, JV Selinger, and RLB Selinger, PNAS110, 3242 (2013).
[2] TS Nguyen, J Geng, RLB Selinger, and JV Selinger, Soft Matter 9,8314-8326 (2013).
[3] LT e Haan, V Gimenez-Pinto, A Konya, TS Nguyen, JMN Verjans, Cs Sánchez-Somolinos, JV Selinger, RLB Selinger, DJ Broer, APHJ Schenning, Advanced Functional Materials 24, 1251 (2014).