Surface Morphology of Syndiotactic Polypropylene Single Crystals Observed by Atomic Force Microscopy

Abstract

We have studied the surface morphology of single crystals of syndiotactic polypropylene (sPP) by atomic force microscopy (AFM). The thickness of a single crystal lath grown at 140 °C was determined by AFM to be 10.5 ± 1 nm. The surface roughness within flat, defect-free areas up to 1 μm across was in the range 0.3-1 nm. A feature of the sPP single crystals was straight cracks about 100 nm wide across the single crystal laths. Three to four cracks were observed on a single-crystal with the average distance between adjacent cracks of 5-10 μm. Smooth periodic undulations in thickness, or wrinkles, were observed. The periodicity of these undulations is about 400 nm and the number of periods can reach 10-30. On the molecular scale, we observed modulations of surface topography with periods of 1.5 and 1.1 nm that are close to the lengths of the a and b edges of the sPP unit cell determined from electron diffraction.