C. Manohar

VESICLE TO MICELLE TRANSITION DRIVEN BY SURFACE SOLID-FLUID TRANSITION

This paper reviews the solution behavior of cetyltrimethylammonium hydroxynaphthalene carboxylate (CTAHNC), which has the unique feature of undergoing a transition from vesicle to worm-like micellar phase in three different ways, namely, increase in temperature, addition of a surfactant and on shearing. Fluorescence anisotropy, NMR, rheology, small angle neutron scattering studies etc gave evidence of the vesicle-micelle transition. CTAHNC can be looked upon as a complex formed by two oppositely charged surfactants (CTA+ and HNC-). This ion pair effectively acts as a double-chain lipid and has a tendency to form vesicles. On increasing the temperature, and/or adding single chain surfactants of shearing, the complex dissociates which changes the curvature energy of the surface. This leads to a surface melting that brings forth the vesicle-micelle transition.

A thermally reversible vesicle to micelle transition driven by a surface solid–fluid transition

This study presents evidence for a vesicle to worm-like micelle transition in solutions of a new surfactant cetyltrimethylammonium hydroxynaphthalenecarboxylate (CTAHNC) driven by a possible coulombic solid–fluid transition on the micellar surface.

Some concepts on design of surfactant gels and vesicles

It is conjectured that anionic-cationic surfactant combination can be regarded as equivalent to a double chain surfactant and using molecular packing considerations it is shown that vesicles, viscoelastic solutions and liquid crystals can be designed by the proper choice of chain lengths of the pair. Using these concepts new systems are designed, from mixtures of cetyltrimethyl ammonium bromide and sodium alkyl sulfonates, to produce both viscoelastic gels and vesicles.

Catanionic surfactants as nanospring suspensions: a model.

A model for a dilute suspension of nanosprings, whose equilibrium configuration and extension are controlled by electrical double layer forces, is presented along with a model for changing packing parameter. The dependence of viscosity on surface charge is calculated. The possibility of shear-thickening is demonstrated. It is argued that mixtures of cationic and anionic surfactants which show two peaks in viscosity and a minimum along with shear-thickening are likely candidates for this model.

Nematic liquid crystalline structures in dilute surfactant solutions

Abstract The nematic phase and the viscous isotropic (VI) phase formed by solutions of CTAB and SHNC are investigated using light scattering and viscosity techniques. It is argued that the turbidity in the nematic phase is due to orientational fluctuations in the director and therefore the intensity scales as Q −2. It is shown that with dilution of the nematic phase with water the turbidity disappears with a simultaneous increase of viscosity.