Dynamic assembly of anionic surfactant into highly-ordered vesicles

A highly-efficient dynamic assembly method for the transformation of the initial spongy lamellar structure of concentrated linear alkylbenzene sulfonate, LAS, incorporated with sodium silicate, into spherulitic vesicles is presented. A combination of drag and pressure flows, via twin screw extrusion, was used to mitigate the ubiquitous viscoplasticity and the wall slip behavior of the anionic surfactant paste and gave rise to the dynamic assembly of stable vesicular nanostructures within a narrow size range, that was not possible with either pure drag or pure pressure flows. Concomitantly with the structure transformation of the paste during assembly under the combination of pressure and drag flows, significant changes in its viscoelasticity, i.e., order of magnitude increases in storage and loss moduli and magnitude of complex viscosity, were observed. The demonstrated dynamic assembly of stable vesicular nanostructures, with vesicle diameters within the relatively narrow range of 300-600 nm, from a commodity surfactant is relevant to myriad templating and encapsulation applications, as well as shedding light on the mechanisms of the deformation-induced planar lamellar to vesicle transformation of concentrated amphiphiles. (C) 2011 Elsevier Inc. All rights reserved.