Research On Photo-induced Wrinkling Of Glassy Nematic Films

Wrinkled surfaces are very attractive in various applications including flexible electronic devices, microfluidics, templating and device fabrication. Much of work have been done to form and control wrinkled surfaces. Nematic liquid-crystal solids with azobenzene moieties deform in response to illumination by contraction along and elongation perpendicular to the director. And the deformation is reversible in the dark. Now, enormous control of director fields in nematic liquid-crystal solids is possible, splay-bend and twist distributions are most typical of complex director distributions. The purpose of this thesis is to form and control wrinkled surfaces by photo-induced instability of splay-bend and twist glassy nematic films on substrates.First, under the isotropic assumption, we treat nematic films as three-dimensional elastomers. And by using eigenstrain theory and linear stability analysis method, we give the critical condition of instability, the averaged wrinkle wavelength and the wrinkling direction. Also, we obtain their relations with the film-substrate modulus ratio.Then, we relax the isotropic assumption. The equilibrium equations of glassy nematic films bonded to a substrate in the case of anisotropy are derived by the Foppl-von Karman plate theory. Through numerical simulations, we get wrinkle patterns, critical conditions of instability, equilibrium wrinkle wavelengths, wrinkling directions and their relations with modulus ratio. And we compare these results with the results of linear stability analysis method.Finally, we study the effect of anisotropy induced by complex director distributions on wrinkling. Through numerical simulations, we obtain the effect of the ratio of elastic modulus in two directions on wrinkle patterns, equilibrium wrinkle wavelength and wrinkling direction when we assume one of the elastic modulus is constant.