Absorption into silicone rubber membranes from powders and aqueous solutions

This study compared the rate and amount of absorption from aqueous solutions and pure powders of 3- and 4-cyanophenol (CP) into silicone rubber (SR) membranes. SR membranes were cast directly onto a zinc-selenide attenuated total reflectance (ATR) crystal, which was then mounted on a Fourier transform infrared (FTIR) spectrometer. CP was presented to the SR membrane from aqueous solutions or powders sufficient to completely cover the membrane surface. The concentration of CP in the membrane at the interface with the crystal was determined by IR absorption of the C triple bond N stretch. The amount of CP in the SR membrane at steady state was determined by extraction and UV absorption measurements of the extract. The concentration of CP in SR membranes was found to depend weakly on the concentration of the aqueous solution. The amount of CP in SR membranes equilibrated with pure powders was essentially the same as for the CP-saturated solutions. Diffusion coefficients for 3 and 4-CP (2.8+/-0.2 and 2.5+/-0.6 x 10(-7) cm(2) s(-1), respectively) were not statistically different. The absorption rate of CP into SR membranes was almost the same from the powder and aqueous solution indicating that the rate of mass transfer from the powder to membrane was larger than 0.04 cm h(-1).