Multilamellar vesicles in a commercial surfactant system

The manufacture of concentrated detergent granules in the detergent industry can be achieved by the incorporation of surfactant pastes, such as linear alkylbenzene sulfonate paste (LAS)-a lamellar liquid crystalline material (surfactant concentration of ca. 78 wt. %). LAS paste was processed at 25degreesC and 60degreesC, in both the absence and presence of sodium disilicate (Na2O:2SiO(2)) additive, and the effect on the formation of shear-induced multilamellar vesicle (MLV) microstructures was studied. Our results suggest that LAS pastes of high hardness and stiffiness are always associated with MLV microstructures and vice versa-these are known as "structured "pastes in industry, and also appear nonadhesive. MLVs are able to form from "pure " LA S at 25degreesC, although, at 60degreesC, sodium disilicate is necessary. With increased processing time, the size of the MLVs decreases and becomes more uniform-pastes are also increasingly hard and stiff. When stored, "structured "pastes eventually revert back to being-soft and sticky, reflecting the metastable nature of the MLVs.