Charge-induced nematic-isotropic transition in mixed surfactant solutions

Rheological characterizations of wormlike micellar solutions containing cationic surfactant and anionic hydrotropic salt

“…In the entangled regime, plateau modulus G 0 only depends on the entanglement mesh size; thus, the difference in these rheological parameters would be indicative of micelle persistence length difference in CTAB/NaSal and CTAB/SHNC systems. Note that the 75 and 100 mM CTAB/NaSal solutions reached a nonmonotonic shear stress plateau without any stress maximum [Dubash et al (2012)], which is consistent with the argument that the counterions from the salt at the micelle surface may change the micelle stiffness and interactions between the neighboring micelles [Mishra et al (1993a[Mishra et al ( , 1993b]. On the one hand, the extra tail in CTAB/SHNC reduces the curvature of CTAB micelles more significantly when compared with the CTAB/NaSal micelles, facilitating elongated micelle formation with smaller packing parameters in CTAB/SHNC micelles.…”

“…Recent studies have used light scattering, flow birefringence, electron microscopy, and rheometric techniques to investigate the material properties of SHNC and cationic surfactant mixtures. Mishra et al (1993aMishra et al ( , 1993b reported the phase behavior of the mixture of cationic surfactant cetyltrimethylammonium bromide (CTAB) and SHNC. By fixing the CTAB concentration at 60 mM and gradually increasing the CTAB/SHNC molar ratio, the CTAB/SHNC mixture underwent phase transitions from small micellar aggregates to a positively charged gel phase, followed by a liquid crystalline lamellar phase, then precipitated into a multilamellar vesicle phase at equimolar surfactant/salt concentration.…”

“…By fixing the CTAB concentration at 60 mM and gradually increasing the CTAB/SHNC molar ratio, the CTAB/SHNC mixture underwent phase transitions from small micellar aggregates to a positively charged gel phase, followed by a liquid crystalline lamellar phase, then precipitated into a multilamellar vesicle phase at equimolar surfactant/salt concentration. In particular, when the concentration ratio of SHNC over cationic surfactant exceeds 1.0, SHNC was observed to inhibit growth or entanglement of micelles by negatively charging micelle surfaces [Abdel-Rahem (2005); Krishnaswamy et al (2005); Mishra et al (1993aMishra et al ( , 1993b]. When the temperature increases or the solution is further diluted, the HNC À ions can actually desorb from the micelles and decrease the surface charge of micelles, which in turn promotes growth of wormlike micelles and enhances the viscoelasticity of the solution.…”

A novel viscoelastic system from a cationic surfactant and a hydrophobic counterion

“…3,2-SHNC hydrophobic counterion mixed with CTAB, was first investigated by Manohar et al [10][11][12][13][14][15][16]. The 3,2-SHNC, which is structurally comparable to SS is strongly adsorbed on the micellar surface with the carboxylate and hydroxyl group protruding out of the micelle.…”

Liquid crystal models of biological materials and silk spinning

“…1,16,37,38 For charged rods, Coulombic repulsion (bZ 2 ) will promote the isotropic phase and the critical rod concentration threshold increases with Z. 16,39 For thermotropic/lyotropic mixtures that undergo the IN transition but no phase separation, DMS predicts that the mixture temperature threshold is a nonlinear function of concentration and molecular weights 16,41,42 ; the mixture IN transition can occur at a temperature lower than the transition temperature of the lower molecular weight component. Nonspherical tactoidal lm sized drops are commonly observed in collagen, viruses, and chitin solutions, under IN* phase coexistence.…”