Liquid-crystalline elastomers (LCEs) are a class of stimuli-sensitive materials that can display reversible thermo-mechanical actuation, soft-elasticity behavior, and changes in optical properties. Recently, a two-stage thiol-acrylate Michael-addition/photo-polymerization reaction has been introduced to synthesize main-chain LCEs. This presentation will discuss how this two-stage reaction can be used as a platform to create a wide range of shape-changing and biomedical applications. A nematic diacrylate mesogen, RM257, is mixed in a non-stoichiometric ratio with a di-thiol spacer and multi-functional thiol crosslinker. Utilizing an excess of acrylate functional groups, the Michael-addition reaction is a click reaction that is self-limited by the number of thiol groups. This first reaction can be used to create polydomain LCE samples. The second stage photo-polymerization reaction is then used to react the excess acrylate groups in a homo-polymerization reaction. The second stage reaction will be shown to program a permanently oriented liquid-crystal monodomain capable of reversible thermal actuation. The magnitude of thermal actuation is shown to increase proportionally with the amount of strain applied during photo-crosslinking. Furthermore, the spatio-temporal control of the UV light can be used to tailor both mechanical and optical properties of the LCE samples. Next, the two-stage reaction process will be combined with electrospun polyvinylalcohol (PVA) fibers to create LCE-PVA mesh composites. By utilizing a water-soluble fiber, such as PVA, the fibers of the composite can be used as a sacrificial template to create an LCE-based filtration device capable of reversible actuation.

Main-chain liquid-crystalline elasomers using a two-stage thiol-acrylate reaction for shape-switching biomedical applications

251st National Meeting (2016)

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