Mass transfer processes induced by inhomogeneous photo-polymerisation in a multicomponent medium

We present a model that accounts for the processes involved in the laser-induced formation of diffraction gratings in polymer-based composites containing liquid crystal molecules in conditions that exclude both phase separation and transition during polymerisation. Starting from an inhomogeneous photo-induced polymerisation of radicals, the reasons leading to a spatial redistribution of the different components are investigated. The model incorporates a realistic kinetic scheme of polymerisation processes and is based on the assumption that redistribution of molecules is due to conventional diffusion of molecules that takes place, however, not in the whole sample, but only in that part which is not occupied by long and immobile polymer chains. Such a restriction gives rise to a diffusion of non-reacting components, as well as reactants and mobile products. Qualitative predictions of the model well agree with experimental results available in literature. (C) 2001 Elsevier Science B.V. All rights reserved.