Multilamellar vesicles in a commercial surfactant system

Dynamic assembly of anionic surfactant into highly-ordered vesicles

“…A highly-viscous concentrated surfactant, i.e., a linear alkylbenzene sulfonate LAS-water paste, reported earlier by Liaw et al [34] was used. This paste is industrially referred to as a ''high active'' LAS paste of ca.…”

“…A multipass capillary rheometer (a capillary die connected to two cylinders/plungers which alternate to force the paste repetitively through the capillary die) was used to apply the shear. The difficulty of structuring of this concentrated surfactant paste is evident by the conditions of the pressure-induced flow during which shearing was applied for 1-3 h. Furthermore, this pressure-driven flow typically generated only about 17 g of structured LAS over durations of up to 1 h of shearing [33,34].…”

“…As the temperature of the surfactant paste in the twinscrew extruder increases to over 65°C the rate of structure formation decreases below that was observed at 60°C (as indicated by lower storage modulus, G 0 , values). These findings are consistent with the experimental findings of McKeown et al [33] and Liaw et al [34] which indicated that the lamellae to vesicle conversion of the LAS surfactant (Fig. 10) only becomes significant over a narrow temperature window and the rate of formation of onion like multilayered vesicles depends exponentially on temperature.…”

“…Léon et al [43] have determined that at least for the aqueous solution of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) at a surfactant concentration of 7%, j is unaffected by the addition of salts, whereasj is affected. Liaw et al [34] suggest that the dissolution of sodium disilicate might give rise to a decrease of the bilayer repeat distance, and/or raise the ionic strength of the water present in the LAS bilayers. This would alter the size of the head-group of the LAS surfactant or change the electrostatic forces within and between layers to thus presumably alter the membrane elastic constant to enable the formation of onion like multilayered vesicles which are interconnected to each other to provide the significant increase in elasticity and viscosity (Fig.…”

“…This pressure-driven flow through a channel gives rise to a distribution of shear rates, _ cðyÞ, with the maximum shear rate occurring at the wall and zero shear rate at the axis of symmetry. McKeown et al [33] and Liaw et al [34] have demonstrated that vesicular structures from linear alkylbenzene sulfonate, LAS, can be obtained upon shearing under such a pressure-driven flow. A multipass capillary rheometer (a capillary die connected to two cylinders/plungers which alternate to force the paste repetitively through the capillary die) was used to apply the shear.…”