Layering and relaxation in molecular films of a photosensitive polyacrylate from X-ray reflectivity and in elastic neutron scattering experiments

In this paper we study the effect of ultraviolet (UV) illumination on the microscopic structure of molecular layers of a photosensitive fragile polymeric glass former. In particular we show that the increased time relaxation and the reduced mobility of thin molecular multilayers recently reported using high-precision pump probe ellipsometric experiments correlate with a geometrically induced layering effect which was confirmed by synchrotron X-ray reflectivity experiments. Furthermore the results agree also with recent inelastic-quasielastic neutron scattering measurements of the coupling between the photosensitive side chains and the polymeric main chain. The observed layering is destroyed upon UV illumination. The significance of such results on the glass transition behaviour of this material is discussed.