Abstract
The water vapor diffusion resistance of artificial membranes (Millipore filters) impregnated with various oils and oil-solid mixtures is compared with the resistance of stratum corneum from excised animal skin and with that of fatty alcohol monolayers. The materials tested include mineral and silicone oils of widely varying viscosities, a liquid triglyceride (cottonseed oil), and suspensions in it of two sparingly soluble solids, cholesteryl palmitate and beeswax. The resistances of the mineral oil membranes were found to increase with oil viscosity but there was no detectable viscosity effect in the series of silicone oils. All the silicones had surprisingly low resistances which were close to that of solid polydimethylsiloxane. The resistance of the triglyceride was less than that of a mineral oil of comparable viscosity. It was further reduced by addition of cholesterol or lecithin but was markedly increased by addition of beeswax and even more so by cholesteryl palmitate. The very high tortuosity factors obtained with the cholesterol ester are attributed to the anisometry of its crystals (thin platelets) and to their orientation in the membrane. Only certain of the oil systems containing suspended solids and the monolayers are comparable to stratum corneum in resistance per unit thickness. The water vapor barrier of this tissue is equal to that of about one hundred monolayers of octadecanol in series.
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