NEXAFS studies on the surface orientation of buffed polyimides

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been used to determine the average near-surface orientation of chains in a buffed polyimide film. Auger and total electron yield measurements provide powerful and direct means of determining the orientation of chains as a function of depth. In the case of a strongly buffed sample, the polyimide chains at the film surface are found to be highly aligned along the buffing direction. We also find significant alignment of the phenyl ring planes parallel to the surface. The alignment is discussed in terms of simple models that are useful in visualizing the alignment in partially disordered systems. The chain orientation decays as a function of distance from the surface, becoming random in the bulk. The 1/e alignment depth is ≃100 Å. Studies as a function of load applied during buffing and distance of buffing show that the near-surface orientation saturates at relatively small loads and short distances. The 1/e buffing load and buffing distance for the near-surface alignment are 1.2 g/cm2 and 67 cm, respectively.