Three-dimensional anisotropies induced by light in thin polymer films

Abstract

The three-dimensional structure of thin anisotropic polymer films is of great importance for many applications, such as display technology and optical data storage. We developed different methods for the accurate determination of the inplane and the out-of-plane anisotropy of thin polymer films. The anisotropic properties are generated or modified by irradiation with polarized light at room temperature and subsequent thermal development of the liquid crystalline polymers. For the characterisation of thin films different ellipsometric methods and absorbance measurements were developed and for thick films the prism coupling method was used. The three-dimensional structure of the films and the resulting optical properties are strongly dependent on thickness and preparation of the films. The photoinduced order is generated by the photoorientation of azobenzene containing side chain polymers. This order is changed by annealing of the films in the liquid crystalline phase of the polymers. For thinner spin coated films the order after annealing is almost a prolate in-plane order. This should be caused by the initial in-plane order induced by the spin coating process. In the case of thicker films the order after annealing is homeotropic due to the interfacial order. Under certain conditions even an oblate order was found after annealing.