AFM Observation of Surface Morphology for Oriented PET Films

Abstract

The atomic force microscopy (AFM) was used to examine surface morphologies for biaxially oriented PET films, and the results were discussed from the view point of strain induced structure formation. For the most of oriented films, the nodular microstructure was observed. Its height and diameter were several nm and 20–50nm, respectively. Although the microstructure was observed also on the surface of as-cast film, its height was less than lnm. The plot of surface roughness measured by AFM as a function of the draw ratio showed that the microstructure had developed gradually with drawing until a certain draw ratio (λ c), but the development had declined after λ c. The AFM images and the behavior of roughness change also showed that a higher order structure like a spherullite was easily formed by annealing for the films undrawn or drawn less than λ c, while the films drawn more than A c were little influenced by the annealing. The strain induced crystallization were examined by wide angle X-ray scattering (WAXS), density and average refractive index measurements. The experimental results suggested that the development of surface microstructure was closely related to the strain induced crystallization, and the strain induced crystallization in the bulk slightly delayed compared with the development of surface microstructure.