Sorption of Organic Solvents in Poly(Dimethyl Siloxane) Membrane. I. Permeant States Quantification using Differential Scanning Calorimetry

The permeant states of various solvents in poly(dimethyl siloxane) (PDMS) film were evaluated using low temperature differential scanning calorirnetry (DSC) on both vapor and liquid penetrants. Water, cyclohexane, benzene, toluene, and m‐xylene may be present in the freezable and nonfreezable state. At low sorption levels, solvents sorbed in PDMS were in the nonfreezable state until a threshold value was reached. Beyond that, the increased solvent sorption values all occurred in a freezable state. The partition pattern between the freezable and nonfreezable states for a vapor penetrant showed an identical trend with that for the liquid penetrant. The maximum nonfreezable amount of solvent in PDMS depended on the solvent's chemical compatibility with the membrane but not on the sorption temperature. Compared with that at 10°C, the higher solvent solubility at 25°C was due to the increase in the freezable solvent content without any change in the maximum nonfreezable content. The permeant states for equilibrium and nonequilibrium samples did not differ from one another.