Formation and dynamics of polymer surface relief gratings

Time resolved VIS and X-ray scattering experiments have been performed duri ng the formation of a surface relief grating on a polymer film containing a n azobenzene side-chain homopolymer (poly{(4-nitrophenyl)[4-[[2-(methacrylo yloxy)ethyl]ethylamino]phenyl]diazene} (pDR1M), T-G = 129 degreesC) upon ho lographic exposure with circularly polarised laser light of 488 nm. Using f ixed geometric conditions for both experiments, the time evolution of the f irst 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 t he X-ray experiment did not create a permanent grating. This is confirmed b y ex situ AFM inspections recorded after holographic treatment. VIS inspect ion with better time resolution reveals an elastic process during the first seconds but plastification of the material for longer exposure times. Part ial relaxation takes place when the light is switched off. Cyclic light tre atments create two periodic density gratings below the surface and a surfac e relief grating as well. Both scattering experiments can be explained qual itatively by finite element calculations assuming a viscoelastic (VE) flow model. (C) 2001 Elsevier Science B.V. All rights reserved.