Effect of surface topographies of PTFE and polyimide as characterized by atomic force microscopy on the heterogeneous nucleation of isotactic polypropylene

The influence of surface topographies of poly-tetrafluoroethylene (PTFE) an d polyimide (PT) on heterogeneous nucleations of isotactic polypropylene (i PP) in the iPP/PTFE and iPP/PI interfacial regions have been investigated m ainly using atomic force microscopy (AFM) and optical microscope with hot s tage. Surface topographies have been characterized by AFM in terms of RMS r oughness (R-a) and fractal dimensions. For PI surface with higher complexit y, i.e. higher RMS roughness (R-a = 2.94 mu m) and higher fractal dimension (2.56), induced more nuclei of iPP and the transcrystalline layer was obse rved at the interfacial region if supercooling was undergoing below 154 deg rees C, On the other hand, transcrystalline layer could be observed on PTFE surface with either higher roughness (R-a= 5.23 mu m, fractal imension = 2 .27) or lower roughness (R-a = 8.94 mu m, fractal dimension = 2.23). All th ese substrate surfaces with higher complexity were more capable of inducing exuberant nuclei. The kinetic mechanism of crystallization of iPP was dete rmined by supercooling instead of substrate nature and its transient temper ature from regime II to regime I is similar to 154 degrees C. Some comments on the previously proposed hypotheses of transcrystallization are also mad e based on the observations in this investigation. (C) 1999 Elsevier Scienc e S.A. All rights reserved.