GALCIT Colloquium

Nematic elastomers are active rubbery solids made of cross-linked polymer chains which have liquid crystals either incorporated into the main chain or pendent from them.  Their structure enables a coupling between the mechanical elasticity of the polymer network and the ordering of the liquid crystals, and this in turn results in fairly complex mechanical behavior (e.g., large spontaneous distortion due to temperature change, soft-elasticity and fine-scale microstructure).

We study thin sheets of nematic elastomer.  First, we show that thin sheets of a particular class of nematic elastomer can resist wrinkling when stretched.  Second, we show that thin sheets of another class of nematic elastomer can be actuated into a multitude of complex shapes.  In order to obtain these results, we systematically develop two dimensional theories for thin sheets starting from a well-accepted first principals theory for nematic elastomers.  These characterize (i) the mechanical response due to instabilities such as structural wrinkling and fine-scale material microstructure, and (ii) thermal actuation of heterogeneously patterned sheets.  For the latter, we show that the theory, which comes in the form of a two dimensional metric constraint, admits two broad classes of designable actuation in nonisometric origami and lifted surface.  For the former, we show that taut and appreciably stressed sheets of nematic elastomer are capable of suppressing wrinkling by modifying the expected state of stress through the formation of microstructure.