Thermodynamic properties of disaccharide based surfactants adsorption at the water-air interface

Abstract

Measurements of the equilibrium surface tension of aqueous solutions of the disaccharide based surfactants: n-dodecyl-β-D-maltoside (DM) and sucrose capric acid (SMD) as well as sucrose lauric acid (SML) esters at 293 K, 303 K and 313 K were made. On the basis of the obtained results the standard Gibbs free energy, standard enthalpy and entropy of DM, SMD and SML adsorption at the water-air interface were calculated. Using the measured values of the equilibrium surface tension of the aqueous solutions of DM, SMD and SML, the Gibbs surface excess concentration of n-dodecyl-β-D-maltoside, sucrose capric or sucrose lauric acids esters and the mole fraction of the area occupied by their molecules at the water-air interface at a given temperature were determined. Next, from the obtained thermodynamic parameters of the studied sugar surfactants adsorption at the water-air interface, temperature and type of head and tail of surfactants impact on their adsorption were deduced and compared to those determined earlier for n-octyl-β-D-glucopyranoside (OGP) and n-dodecyl-β-D-glucopyranoside (DDGP). The changes of the standard Gibbs free energy of DM, SMD and SML adsorption at the water-air interface indicate that their tendency to adsorb at the water–air interface comes down as the temperature decreases. Small values of ΔHads0 suggest that in the studied temperature range dehydration of the DM, SMD and SML molecules does not occur.