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

Measurements of the equilibrium surface tension of aqueous solutions of the disaccharide based surfactants: n-dodecyl-beta- 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-beta-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-beta-D-glucopyranoside (OGP) and n-dodecyl-beta- Dglucopyranoside( 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 Delta(0)(ads) suggest that in the studied temperature range dehydration of the DM, SMD and SML molecules does not occur.