Chemical structure and surface activity

Surface tension measurements on aqueous solutions of 2-alkyl-2-methyl-1,3-dioxolanes, 2-alkyl-4-methyl-1,3-dioxolanes, and 2-alkyl-1,3-dioxanes at a temperature of 293.2 K are presented. The surface tension isotherms obtained were used to calculate some adsorption parameters, i. e. the efficiency of surface tension reduction, pC₂₅, surface excess concentration, , and surface area,A, per molecule in the adsorption layer. The Temkin adsorption isotherm equation was used to calculate standard free energy of adsorption, G⁰_=0.5 . The increments for a methylene group in the alkyl chain, G^o [–CH₂–], and for the residual part of the molecule, G^o [W], were also determined.The results obtained show that: (i) an increase in alkyl chain length at the C-2 carbon atom of the ring by one methylene unit brings about a marked increase in surface activity; (ii) the introduction of a methyl group into the 1,3-dioxolane ring (i. e., at C-2 or C-4 atom) has a weaker effect on surface activity of alkyl-substituted 1,3-dioxolanes, and (iii) the contribution of the 5- and 6-membered 1,3-dioxacyclane rings to a total surface activity of, respectively, 2-alkyl-1,3-dioxolanes and 2-alkyl-1,3-dioxanes is similar.