Partial molar volumes of surface-active agents in aqueous solution

The partial molar volumes text-decoration:overlineV2 of some ionic and non-ionic surface-active agents have been determined above and below the critical micelle concentrations. The change Δtext-decoration:overlineV2 in partial molar volumes on micelle formation is determined by molecular structure. Thus, additional methylene groups in the alkyl chain remote from the hydrophilic group give an increase in Δtext-decoration:overlineV2, while additional methylene groups in close proximity to a hydrophilic centre give a small decrease in Δtext-decoration:overlineV2. These results indicate that in the process of micelle formation the hydration of the methylene groups adjacent to the hydrophilic group is retained.