Krafft points and microemulsion phase behavior of some alkylarenesulfonates

Abstract

A number of alkylarenesulfonate surfactants of high purity were synthesized to study their properties in solution. The microemulsion phase behavior and Krafft point were significantly influenced by the surfactant molecular structure. Within the linear alkylnaphthalene series, an inverse relationship was found between surfactant chain length and optimal salinity, whereas oil solubilization was observed to increase with the chain length. The cosolvent chain length had an inverse effect on optimal salinity and a direct effect on the oil uptake while the opposite effects were observed with oil phase chain length. The Krafft points of the sulfonates were observed to decrease as the symmetry of the surfactant molecule decreased. Consequently, the Krafft points of alkylnaphthalenesulfonates decreased as the branching of the alkyl chain increased. In addition, aqueous solution salinity was found to increase the surfactant Krafft point. This, in turn, had a significant effect on the microemulsion phase behavior of the sulfonates in the presence of various oils and brine. The linear alkylnaphthalenesulfonates required high levels of cosolvent alcohols (surfactant/cosolvent = 1 2 ) to exhibit complete microemulsion phase behavior. The highly branched bilinear analogs still needed cosolvent but to a much lesser extent (surfactant/cosolvent = 2 1 ).