Electrolyte effects on the surface tension and micellization of n-dodecyl beta-D-maltoside solutions

Sugar-based surfactants such as polyglucosides are a relatively new class of nonionic surfactants portrayed to be suitable for high-salinity applications. To better utilize such surfactants, it is useful to elucidate the mechanisms of their interactions at various interfaces in the presence and absence of electrolytes and the reasons for their salt tolerance. In this work, the effect of various salts on the surface tension and critical micelle concentration of the nonionic surfactant n-dodecyl beta-D-maltoside (DM) was studied. Interestingly, while the packing of DM molecules at the air-water interface was not affected by the nature of salt added, cations and anions were found to have markedly different effects on the surface activity and critical micelle concentration (cmc) of the surfactant. For the same cation Na+, the effect of anions decreases in the order F- > Cl- > SO42- > Br- > PO43- > citrate > I- > SCN-. For the same anion Cl-, the effect of cations follows the order K+ > Na+ > Rb+ > Li+ > Ca2+ > Al3+. The effectiveness of the salts is correlated with the charge to radius ratios of the ions, and it is clear that cations and anions have disparate effects. The results are discussed in terms of the structure-making and structure-breaking properties and solvation heats of ions.