Multiresponsive polymeric microstructures with encoded predetermined and self-regulated deformability

Abstract

SignificanceThe range of allowed deformation modes currently described for the actuation of microstructures is limited. In this work we introduce magnetic-field–guided encoding of highly controlled molecular anisotropy into 3D liquid-crystalline elastomer microstructures capable of displaying unique multiresponsive, shape-changing behaviors. The richness of the predetermined and self-regulated deformations and region-specific motions in these microstructural arrays gives rise to physicochemical insights, as well as potential applications in controlled adhesion, information encryption, soft robotics, and self-regulated light–material interactions.

Liquid Crystal Templates Combined with Photolithography Enable Synthesis of Chiral Twisted Polymeric Microparticles

“…In addition, the reactive mesogens used here were of a single type, simple diacrylate mesogens with a rigid main body, which resulted in a single shrinking response upon extraction of the unreacted mesogens. Future studies may also be devoted to the design of microparticles using multiple types of reactive mesogens to provide more complex shapes, as well as response to the external stimuli such as light, chemicals, magnetic field . In the long term, such microparticles have the potential to be useful in applications ranging from emulsion stabilization, intracellular delivery, sensors, biocatalysis, and photonics.…”

Twist again: Dynamically and reversibly controllable chirality in liquid crystalline elastomer microposts

“…The alignment of the liquid crystal mesogens produces a corresponding anisotropy in the conformations of the polymer chains. By cross-linking the chains while the mesogens are in the aligned, nematic liquid crystal state, the resulting elastomer exhibits the specific nematic director orientation present at the time of cross-linking (19). Disrupting the nematic ordering through heating (23,24) or UV light induces a contraction along this director and an expansion in the two orthogonal directions.…”

“…Our continuum model of LCEs allows us to capture the macroscopic response of the material due to conformational changes of the constituent polymer chains (19). Within this framework, we use the Gent model (25) for rubber elasticity to describe the resistance of the material to shear deformations.…”

“…When the light source is removed, the polymers relax, and the previously illuminated region of the elastomer returns to its ordered state. While the photoresponse of an individual azobenzene molecule can occur on a time scale of 10 −9 s or less (32), the resulting mechanical equilibration of the microposts occurs on a time scale of minutes (19), longer than can be simulated in a reasonable time frame, so we omit the specific details of the excitation and relaxation rates. Diffusion of heat across the dimensions of the micropost is expected to occur on a time scale of several microseconds to milliseconds (33), allowing us to ignore thermal gradients within the material.…”

“…The elastomers modeled here are fabricated from monomers containing side-chain mesogens, which are aligned along a specific direction by an applied magnetic field (19). [Notably, compared to the additive manufacturing of LCEs in which the mesogens can only be oriented parallel to the printing direction (20), the use of a magnetic field before polymerization allows an arbitrary mesogen orientation prescribed to the LCE by the external field.]…”