The fundamental topology of cellular structures -- the location, number, and connectivity of nodes and compartments -- can profoundly impact their acoustic, electrical, chemical, mechanical, and optical properties, as well as heat, fluid and particle transport. Approaches harnessing swelling, electromagnetic actuation as well as mechanical instabilities in cellular materials have enabled a variety of interesting wall deformations and compartment shape alterations, but the resulting structures generally preserve the defining connectivity features of the initial topology. Achieving topological transformation presents a distinct challenge for existing strategies: it requires complex reorganization, repacking, and coordinated bending, stretching, and folding, particularly around each node where elastic resistance is highest due to connectivity. This presentation will introduce a two-tiered dynamic strategy to achieve systematic reversible transformations of the fundamental topology of polymeric cellular microstructures that can be applied to a wide range of material compositions and geometries. Our approach only requires exposing the structure to a solvent whose composition is selected to have the ability to first infiltrate and soften the polymer through chemical interactions at the molecular scale, and then, upon evaporation, to form a network of localized capillary forces at the architectural scale that zip the edges of the softened lattice into a new topological structure, which subsequently re-stiffens and remains kinetically trapped. Guided by a generalized theoretical model connecting cellular geometries, material stiffness and chemistries of the chosen solvent-polymer pairs, we demonstrate programmed reversible topological transformations of various lattice geometries made of liquid crystalline polymers, undergoing fast global or localized deformations. We then harness dynamic topologies for developing active surfaces with information encryption, selective particle trapping and bubble release, and tunable mechanical, chemical and acoustic properties.

Chemically induced topological transformations of cellular microstructures made of liquid crystalline polymers

ACS Fall 2021

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