Chemische Struktur und Wasserdampfdurchlässigkeit dünner Filme auf Wasser und auf lebender Haut

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Abstract
The permeability to water vapor of monomolecular films of fatty substances on water surfaces depends on the chemical structure of the molecules forming the film. In general, the film must possess a sufficiently high degree of condensation in order to retard the diffusion of water vapor. Expanded and liquid-expanded films do not retard the evaporation of water. Films of straight chain compounds (n-fatty acids, their ethyl esters and glycerides, and primary alcohols) show a marked retardation of water evaporation from C16 onwards. Mono- and poly-molecular films of methyl branched fatty acids and alcohols do not retard the evaporation of water; there are exceptions to this among substances like 17-methyl stearic acid, where the methyl group is far removed from the carboxyl end, which retard evaporation slightly. Octadecanol and its acetyl and propionyl esters are active, but all its higher esters are completely inactive. Trans-brassic acid is highly active, whereas cis-brassic acid is completely inactive on account of its small packing density in the film. On living skin polymolecular films of vaseline and to a lesser extent of ethyl palmitate, show a high covering power. Branched and intermediate fatty acids, and their glycerides, do not retard the evaporation of water from skin.