THE USE OF FOURIER-TRANSFORM INFRARED (FT-IR) SPECTROSCOPY TO DETERMINE THE DIFFUSION-COEFFICIENTS OF ALCOHOLS IN POLYDIMETHYLSILOXANE

A variable long path gas cell was used to measure the sorption of organic vapors by a polymer slab. Unfilled polydimethylsiloxane (PDMS) slabs were cast and used to study the sorption of a series of aliphatic alcohols. The PDMS slab was suspended in the gas cell and exposed to low relative pressures of an alcohol vapor. The sorption rate of the alcohol vapor by the PDMS slab was obtained by measuring the decrease in the amount of free diffusant in the gas cell. The diffusion coefficients of the alcohols in the PDMS slab were then calculated from the curves of amount of diffusant sorbed versus time. The results show that the values of the diffusion coefficients at nearly infinite dilution, Do, for methanol, ethanol, I-propanol, and l-butanol are 1.01 x 10(-5), 0.61 x 10(-5), 0.54 x 10(-5), and 0.33 x 10(-5) cm(2)/sec, respectively. The isotherms for the sorption of the alcohols by the PDMS slab were also constructed from the data.