Applications of grazing incidence diffraction to polymer surfaces

Grazing incidence X-ray diffraction provides a powerful method for determining the structure of the surface region of a polymer thin film. By varying the angle of incidence of the X-ray beam around the critical angle for total reflection of the film, the penetration depth can be tuned to allow a direct comparison of molecular ordering in the surface and bulk of the film. Its application to polymer surfaces is illustrated by in situ studies of the kinetics of crystallisation at the surface of thin films of poly(ethylene terephthalate) (PET) and poly(9,9-dioctylfluorene) (F8), a blue-emitting semiconducting polymer. The results show that ordering occurs significantly faster in PET at the surface in the temperature range 85-100degreesC (close to the bulk glass transition temperature of 75degreesC). F8 also shows more rapid ordering at the surface than in the bulk of the film at 87degreesC. Possible application to developing high-mobility channel regions for polymeric field effect transistors are discussed. (C) 2004 Elsevier Ltd. All rights reserved.