Freeze−Fracture Electron Microscopy of Sheared Lamellar Phase

Abstract

It has been shown recently that shearing of lyotropic lamellar phases may lead to the formation of relatively monodispersed multilayered vesicles named spherulites. Freeze−fracture electron microscopy analysis of such preparations, presented here, shows that their three-dimensional organization is of a space-filling polyhedral type, built up from very closely packed spherulites, without any visible additional water present neither in the center of the spherulites nor in between them. Dilution of these preparations leads to the separation of individual spherulites without appreciable changes of their internal structure (multilayered nature and spacing between the layers). Diluted spherulites become spherical and are separated by the water dispersions of much smaller vesicles, originating probably from the fragmentation of some external layers of concentrated spherulites.

Equilibrium onions?

“…The vesicles fill space and remain in the one-phase region without expelling solvent, by distorting into space-filling polyhedra [14]. The resulting texture is a lattice of disclinations which can be either disordered [11] or ordered [13].…”

“…However, in the concentrated regime monodisperse onions cannot fill space without nontrivial deformations [14]. Typically, onions formed under shear pack as polyhedra, with the deformation of layer j concentrated along the edges of length r j with curvatures of order 1/ξ, where the smectic bending penetration length ξ = K/B depends on the bending K = κ/d and compressionB moduli of the lamellar phase [20].…”

Unusual formation of small aggregates by mixing giant multilamellar vesicles

“…Vesicles are typically made from lamellar liquid crystalline dispersions by various mechanical and/or chemical methods that act to disrupt the regular stacking of the bilayers to produce separated bilayer sheets [1,2]. Shearing bulk-surfactant lamellar phases can also produce multilamellar liposomes that can also be used to entrap soluble materials [3]. However, any of these processes that depend on specific mechanical or chemical steps produce a microstructure that is inherently metastable.…”

Effects of Cetylpyridinium Chloride on Phase and Rheological Behavior of the Diluted C12E4/Benzyl Alcohol/Water System

“…The microstructure of the bilayer-type phases is determined by two factors: the interfacial topology and the degree of connectivity (3). Moreover, their microstructures can be modified under shearing forces (4,5).…”