Direct observation of poly (propylene)-block-poly (ethylene-co-propylene) molecules by atomic force microscopy

Atomic force microscopy (AFM) has been applied to get molecular images of diblock poly(propylene)-block-poly(ethylene-co-propylene) copolymers deposited on mica from diluted solutions at elevated temperatures. Both isolated molecules and their small aggregates have been visualized as compact particles of various sizes with out-spreading poly(ethylene-co-propylene) chains. On the base of the height, volume and morphological analysis AFM images were divided into three groups. In the first group the compact particles are suggested to be small regular-shaped crystallites formed by a few poly(propylene) blocks. Some isolated particles of this group were connected with single copolymer chains. In the second group the compact particles have large dimensions and irregular or round shapes implying unordered packing of constituents. The third group were represented by isolated poly(ethylene-co-propylene) coils. The two-dimensional expansion of coils on mica both isolated and included in aggregates exceeds several times their dimensions in a solution. The two-dimensional expansion of coils on mica both isolated and included in aggregates exceeds several times their dimensions in a solution. The probable mechanism of such an expansion is proposed relying on the existence of van-der-Waals surface force field of a sufficient strength in the vicinity of the crystal surface.