Analyzing the Diffusion Process for Polymer Solution Using FTIR-ATR Technique: Special Considerations

Diffusion of small molecules through the polymers has significant importance in different scientific and engineering fields such as medicine, textile industry, membrane separations, packaging in food industry, extraction of solvents and of contaminants, and etc. This paper reports the use of Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and partial least squares (PLS) analysis to study the compositional change of polymer solution exposed to the certain atmosphere. Diffusion coefficient of tetrahydrofuran (THF) in solution of polystyrene was obtained by means of analyzing the spectral data collected by FTIR-ATR instrument. Desorption by which the solvent evaporates from boundary of polymer solution, with respect to the time, showed that three regions of compositional change appeared: plateau, steep slope, and gentle slope regions. Providing the desorption data from the second region which is the essential part of mass transfer, the value of diffusion coefficient of THF was obtained 5.8 ×10-6 cm2/sec. Finally, affecting factors and limitations of FTIR-ATR technique on reliability of spectral data are discussed.