Polydomain Liquid Crystal Elastomers

Kaushik Bhattacharya

Professor of Mechanics and Materials Science

California Institute of Technology

Liquid crystal elastomers are rubbery materials that possess liquid crystal order.  They undergo a large spontaneous deformation as they undergo a symmetry-breaking isotropic to nematic transition.  Consequently, they are able to display unusually soft behavior by the formation and evolution of fine-scale microstructure.  This soft behavior is of interest to various applications including actuation.  After a brief background, this talk will present a theory that describes the overall mechanical properties of these materials.  An important outcome of the theory is to show that the soft behavior depends critically on the liquid crystal phase in which the material is cross-linked to form the elastomer.  The talk will also describe recent results concerning the non-intuitive mechanical  behavior of thin membranes of these materials.  Joint work with John Biggins, Fehmi Cirak, Qing Long, Carl Modes and Mark Warner.


We consider the equilibrium stress strain behavior of polydomain liquid crystal elastomers. We show that there is a fundamental difference between elastomers crosslinked in the high temperature isotropic and low temperature aligned states. Those crosslinked in the isotropic state then cooled to an aligned state will exhibit extremely soft elasticity — indeed softer than any monodomain sample — and ordered director pattens characteristic of textured deformations. Those crosslinked in the aligned state will be mechanically much harder and characterized by schlieren disclination textures.



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