Covalent adaptable chemistry is a powerful tool to control the shape, bond connectivity, and underlying molecular orientation in covalently crosslinked polymer networks. We have implemented reversible addition fragmentation chain-transfer (RAFT) moieties in the backbone of liquid crystalline networks (RAFT-LCNs) which enables spatial and temporal control over the alignment of the mesogens embedded in the polymer backbone. The RAFT bond exchange process is facilitated via a radical mediated process that can be initiated through photoinduced cleavage of widely available radical photoinitiators thus enabling spatial and temporal control. In this work, we show recent progress in the development of RAFT-LCNs to control the optical properties, surface topography, and bulk shape changes in these novel light responsive LCNs. RAFT bond exchange stabilizes thermally driven disruption in pre-aligned, monolithic nematic LCNs which we leverage to develop optical images and thermoreversible images into pre-aligned RAFT-LCNs. Controllable variables such as exposure temperature, intensity, and time were found to contribute to the resulting birefringence that enabled complex gray-scale images and regions of varying birefringence to be developed with RAFT bond exchange. We repeated this process on pre-aligned surface coatings and found that disrupted regions protrude from the coating and form surface topography that corresponds to the extent of covalently stabilized disruptions. Finally, macro shape change was demonstrated by using the RAFT bond exchange to program thermoreversible shape change. The extent to which RAFT bond exchange alters the low temperature and high temperature shapes were highly dependent on the bond rearrangement conditions including strain, stress relaxation, temperature, and exposure conditions. The bond rearrangement process is repeatable over multiple cycles as long as photoinitator remained. We demonstrated several types of thermoreversible shape changes including simple expansion/ contraction, surface patterns, and hierarchical thermoreversible folding. RAFT-LCNs thus represent a fundamentally new avenue to develop complex shape changing materials.

Photoinduced plasticity in crosslinked liquid crystalline networks: A route to photopolymerizable, programmable shape shifting materials

254th National Meeting (2017)

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