Nematic Phase Liquid Crystal Polymer Sheet Optical Drive The Bending Behavior Analysis

Liquid crystal polymer (LCP) network are a sort of ordered polymers with cross-linking rod-like liquid crystal moieties. On one hand, this kind of synthetic new materials still show some characteristics of liquid crystal such ordering alignments. On the other hand, it can undergo mechanical deformation like some polymers. More importantly, LCPs as a smart material can occur spontaneous mechanical deformation upon temperature, electromagnetic, optical field, etc.In this paper, in light of the recently reported opto-mechanical effect "light-driven bending", we study the optical drive bending behaviors of plate components. And we also attempt to understanding mechanism of bending. Our outcomes can provide a theoretical reference in the process of designing the Micro-Opto-Mechanical Systems (MOMS). Some fantastic bending behaviours of LCP thin plate arise from the effects of irradiation patterns, molecular alignments, boundary conditions, initial sample shape, etc.Firstly, for diffused ultraviolet(DUV) and linearly polarized ultraviolet(PUV) illumination, the irradiation direction, polarization direction and nematic order are introduced into the process of isomerization and light absorption, respectively.Next, in order to study the effects of molecular alignments on bending, we discuss the bendings of both monodomain nematic(parallel and vertical alignments) and poly-domains LCPs upon illumination. For the mono-domain nematic LCPs, the effects of light are coupled into light-induced strains. For the poly-domain nematic LCPs, the corresponding light-induced strains for those poly-domains are obtained by using the Mori-Tanaka mean field method. In addition, we also define the equivalent light-induced Poisson's ratio for denoting the anisotropy of light-induced strains. The equivalent light-induced Poisson's ratio in monodomain alignments straongly depends on crosslinking density and is independent on light source. However, it heavily depends on the light source in polydomain alignments.Moreover, ignoring the light-induced gradient of elastic moduli and basing on the linear elastic material assumption, in limit of small deformation, a bending model of a LCP rectangular plate was constructed. The light-induced bending governing equation and boundary conditions were developed by introducing light-induced moments. Upon uniform illumiantion, the bending effect is divided into two parts:the bending magnitude depending on light sources; the bending shape depending on boundaries, nematic director, etc. In the limit of isotropic material assumption and uniform illumination, analytical solutions of deflection for the two typical boundary conditions involving four free edges and four simple supported edges are derived. Anisotropic bending shape in terms of deflection and Gauss curvature is discussed. Considering the anisotropy of elastic moduli, we simultaed the bending behaviours of a LCP thin plate upon uniform and local illumination with several typical boundary conditions by means of FEM.For a thin plate structure, we discuss the effects of some parameters, such as light intensity, exposure time, polarization angle, the nematic director, the ratio of anisotropic modulus, the equivalent light-induced Poisson's ratio, geometry ratio on light induced bendings. Besides, we compare the difference of between local and uniform irradiation.