Diffusion of benzocaine in poly(ethylene-vinyl acetate) membranes: Effects of vehicle ethanol concentration and membrane vinyl acetate content

Abstract

The effect of vehicle ethanol concentration and membrane vinyl acetate (VA) content on the diffusion properties of poly (ethylene-vinyl acetate) (EVA) membranes was studied. The maximum flux of a model drug, benzocaine, through EVA membranes increases with increasing ethanol concentration and membrane VA content. The flux enhancement is attributed to the increases of both benzocaine membrane solubility and diffusivity. For any given ethanol concentration, increasing membrane VA content increases both solubility and diffusivity of benzocaine due to the amorphous nature of VA, which contributes to higher polymer chain mobility. For the membrane with a given VA content, increasing ethanol concentration results in the increased diffusivity due to membrane swelling by ethanol. The effect of ethanol concentration on benzocaine membrane solubility appears to be much less than the effect on the diffusivity. The relationship between diffusivity and membrane swelling is in excellent agreement with the general free volume theory.