Atomic force microscopy of single polymer chains on a substrate at temperatures above the bulk glass transition temperatures

Abstract

Polymer chains adsorbed on substrates have been observed by atomic force microscopy (AFM); however, observations at high temperatures are not well studied. We observed isolated chains of isotactic and atactic poly(methyl methacrylate) (it-, and at-PMMA) and poly(2-vinyl pyridine) (P2VP) on mica up to 200 °C, which is above their bulk glass transition temperature (Tg), and found that isolated chains could be observed even at temperatures much higher than the bulk Tg. The thicknesses of the chains were constant up to 200 °C, but the radius of gyration (Rg) of the chains started to decrease at 100 °C for it- and at-PMMA and at 150 °C for P2VP. In situ AFM observations indicated that the chains started moving at these temperatures, which were approximately 40, 0, and 55° above their bulk Tg. The restricted movements of the isolated chains should provide useful information to understand the surface phenomena of polymers at the molecular level.