Surface Relaxations in Polymers

ABSTRACT: Near-edge X-ray absorption fine structure, NEXAFS, spectroscopy was used to investigate the relaxations of polystyrene, a typical amorphous polymer, near a free surface after the imposition of a small deformation. Using synchrotron radiation, the NEXAFS dichroic ratio was determined for both the Auger and total electron yield processes as a function of temperature to determine the orientation of the polymer in the first 1 and 10 nm from the free surface, respectively. Complete relaxation of the polymer was not seen for temperatures less than the bulk glass transition temperature. No evidence of enhanced mobility at the free surface was found. A planar relaxation of the polymer was found in the first nanometer from the free surface, whereas in the first 10 nm, the dominant relaxation was normal to the surface. For atomic and molecular solids the breaking of symmetry by a surface strongly influences the funda-mental thermodynamic properties of a material, as, for example, the melting point of the solid near a surface.1-3 Similar issues arise with polymers.4-8 In the case of amorphous polymers, the mobility of the polymer chains at a surface or interface influences, for example, th