Unifying relations in polymer photomechanics

Abstract

Photoresponsive polymers offer novel methods for morphing applications due to its unique ability to control shape spatially and temporally with light. The constitutive behavior of these materials is complicated by the interactions of time-dependent light fields and molecular conformation changes within the polymer network. This requires applications in non-equilibrium thermodynamics, nonlinear photomechanics, and high fidelity numerical simulations using finite difference/finite element methods. The proposed approach utilizes a set of electronic order parameters to represent light driven molecular conformation changes which are coupled to mechanics of a continuum scale polymer network and time-dependent electromagnetics. The model is applied to explain photoisomerization of azobenzene as it deforms a polymer during different types of light excitation. We consider local surface deformation from laser beams including linearly and circularly polarized lights where the azobenzene liquid crystal microstructure couples to affine deformation of the host polymer network. This local deformation from a laser beam is compared to homogeneous polarized light across the surface of a cantilever film. Non-trivial deformation is predicted and the internal mechanisms associated with bending in different directions is discussed.