NONIONIC SUGAR-BASED SURFACTANTS - SELF-ASSEMBLY AND AIR WATER INTERFACIAL ACTIVITY/

The air/water interfacial activity and self-assembly of the mono-dodec yl esters of glucose, sucrose, raffinose and stachyose have been inves tigated. These four non-ionic surfactants provide a series where the h ydrocarbon chain length is invariant while the surfactant headgroup se quentially increases in size. The minimum area per surfactant molecule at the air/water interface increases smoothly with the sequential add ition of galactose structural units, sucrose < raffinose < stachyose, but the galactose units appear not to lie in the plane of the interfac e. The free energy of micellization increases linearly with the number of galactose units. For binary surfactant/water systems, the glucose surfactant exists as hydrated crystals at relatively low temperatures and forms lamellar phases at high temperatures, i.e. an L(beta) follow ed by an L(alpha) phase as the temperature is increased. At a low weig ht percentage of surfactant, the other three surfactants form isotropi c micellar phases. At relatively higher weight percentages of surfacta nt, the sucrose surfactant forms hexagonal and Lp phases, the raffinos e surfactant forms discrete cubic micellar and hexagonal phases, and t he stachyose surfactant begins to crystallize. At a very high weight p ercentage of surfactant, the sucrose, raffinose and stachyose surfacta nts exist as hydrated crystals. Most of the self-assembly behaviour in water can be readily explained in terms of the geometric packing cons traints.