Lyotropic Phases of Dodecylbenzenesulfonates with Different Counterions in Water

Abstract

The lyotropic phase behavior of (technical grade) dodecylbenzenesulfonates (DoBS) is strongly influenced by the type of counterion and the relative amount of water. Phase diagrams are composed for the following systems: HDoBS/water, NaDoBS/water, (HDoBS + NaDoBS 1:1)/water, LiDoBS/water, KDoBS/water, CsDoBS/water, Ca(DoBS)2/water, NaDoBS/water/NaCl, and NaDoBS/water/CsCl. The phases were characterized by light microscopy, freeze-fracture electron microscopy, X-ray diffraction, and macroscopic appearance. The phase diagrams all contain large areas of lamellar phases. The appearance of the lamellar phases differs along this series, in particular regarding swelling behavior, either with or without a micellar phase next to the lamellar phase, and formation of large, rather irregular lamellar units versus smaller, perfectly spherical lamellar topologies (so-called lamellar droplets). LiDoBS shows, in addition, a hexagonal phase between 25 and 50 wt %. Explanations for the occurrence of the different phases are given in molecular terms and in terms of interactions between bilayers and between aggregates.