Examination of solvent interactions at the surface of poly(ethylene) terepthalate films using atomic force microscopy and infrared spectroscopy

Environmental stress cracking of polymeric materials in the presence of solvents is a well-known phenomenon in which a stressed polymer exposed to solvents will exhibit premature crazing and eventual failure. Here we examine the solvent-polymer interaction between poly(ethylene) terepthalate (PET) films prepared by a spin coating technique and the solvents including water, isopropanol, and nitroethane. The interaction was followed using both tapping-mode atomic force microscopy (AFM) and Fourier transform infrared-attenuated total reflection spectroscopy(FTIR-ATR). Using these methods, we hope to gain a better understanding of the effects of solvent interaction at the surface of these polymer films, and of the mechanism of the stress cracking phenomenon. We examine the morphological characteristics of the films as a function of exposure time to the various solvents, by acquiring both in situ AFM images of the polymer in the solvent, and post-immersion imaging of the solvent-exposed polymer in air. We also correlate the AFM images to more quantitative measurements of the degree of polymer crystallinity as measured by the FTIR-ATR technique. By appropriate choice of solvents we can independently examine the effects both of varying the solubility parameter of the solvent component of the polymer-solvent system and of hydrolysis or esterification of the polymer by the solvent. (C) 1999 Elsevier Science B.V. All rights reserved.