Temperature impact on the water-air interfacial activity of n-octyl and n-dodecyl-β-D-glucopyranosides

The water-air interfacial activity of alkylglucopyranoside surfactants with various hydrophobic parts at different temperatures was investigated. For this purpose the measurements of equilibrium surface tension of n-octyl-beta-Dglucopyranoside (OGP) and n-dodecyl-beta-D-glucopyranoside (DDGP) aqueous solutions at different temperatures were made. On the basis of the obtained results the activity, effectiveness and thermodynamic parameters of OGP and DDGP adsorption at the water-air interface were determined. The changes of the standard Gibbs free energy of adsorption calculated on the basis of the Langmuir equation at different temperatures indicate that the tendency of OGP and DDGP to adsorb at the water-air interface comes down as the temperature decreases. The positive values of the standard enthalpy and entropy of OGP and DDGP adsorption imply that bond breaking predominates in their adsorption process and that the studied systems become more random after the adsorption. This indicates that the adsorption process of the studied surfactants is entropy controlled and is associated with the changes in the intermolecular interactions between the sugar surfactants molecules, rather than with the dehydration process.