FTIR imaging of polymer dissolution. 2. Solvent/nonsolvent mixtures

transform infrared (FTIR) spectroscopic imaging employing focal plane array (FPA) detection is used to study the dissolution of poly(alpha -methylstyrene) (PAMS) by solvent solutions containing systematically varied amounts of a nonsolvent. Sequential images were acquired as dissolution proceeded and the samples were not disturbed during image acquisition. Qualitative spatial and chemical distribution of each species within the field of view was obtained by analyzing images based on the characteristic vibrational modes of each species, while quantitative information was gathered through the calculation of individual concentration profiles along the chemical gradient. The images and absorbance profiles showed selective solvent penetration in all cases. In general, the dissolution rate of the polymer decreased linearly with the weight-percent of nonsolvent present in the solution. Anomalously high dissolution rates were observed for solutions containing similar to5-10% nonsolvent. This increase was attributed to the formation of a band of high polymer concentration perpendicular to solvent diffusion direction during the dissolution process. The efficacy of FTIR imaging in studying the spatiotemporal variation of microscopic gradient evolution in multicomponent systems is underscored.