Formation and dynamics of polymer surface relief gratings

Time resolved VIS and X-ray scattering experiments have been performed during the formation of a surface relief grating on a polymer film containing an azobenzene side-chain homopolymer (poly{(4-nitrophenyl)[4-[[2-(methacryloyloxy)ethyl]ethylamino]phenyl]diazene} (pDR1M), T-G = 129 degreesC) upon holographic exposure with circularly polarised laser light of 488 nm. Using fixed geometric conditions for both experiments, the time evolution of the first order grating peak was observed. Short time illumination with a light pattern of about 50 mW/cm(2) shows that the evolution of the VIS and the X-ray signal depends on the pulse length of exposure. Several elastic as well as plastic processes appear. The shortest pulse length of 5 s applied at the X-ray experiment did not create a permanent grating. This is confirmed by ex situ AFM inspections recorded after holographic treatment. VIS inspection with better time resolution reveals an elastic process during the first seconds but plastification of the material for longer exposure times. Partial relaxation takes place when the light is switched off. Cyclic light treatments create two periodic density gratings below the surface and a surface relief grating as well. Both scattering experiments can be explained qualitatively by finite element calculations assuming a viscoelastic (VE) flow model. (C) 2001 Elsevier Science B.V. All rights reserved.