A novel viscoelastic system from a cationic surfactant

taotao477

novel system is compared with the published one of 3-hydroxy-2-naphthoic acid (3,2-HNC) mixed with CTAOH. We investigated the phase
behavior and properties of the phases in aqueous solutions of 100 mM CTAOH with 2,1-HNC. In both systems a multilamellar vesicle phase
is formed when the naphthoate/surfactant ratio (r) reaches unity. When an increasing amount of 2,1-HNC is mixed with a micellar solution
of 100 mM CTAOH, an isotropic low-viscous micellar solution, a viscoelastic gel (consisting of rodlike micelles), a turbid region (two-phase
region), and a viscoelastic liquid crystalline gel (consisting of multilamellar vesicles, MLV) were formed. The vesicular phase is highly
viscoelastic and has a yield stress value. The transition from the micellar to the vesicle phase occurs for CTAOH/2,1-HNC over a two-phase
region, where micelles and vesicles coexist. Also it was noticed that 2,1-HNC is dissolved in 100 mM CTAOH until the naphthoate/surfactant
ratio reaches ∼ 1.5, and the liquid crystalline phases were found to change their color systematically when they were viewed between two
crossed polarizers. The vesicles have been characterized by differential interference contrast microscopy, freeze-fracture electron microscopy,
and cryo-electron microscopy (cryo-TEM). The vesicles were polydisperse and their diameter ranged from 100 to 1000 nm. The interlamellar
spacing between the bilayers was determined with small angle neutron scattering and agrees with the results from different microscopical
methods. The complex viscosity rises by six orders of magnitude when rodlike micelles are formed. The complex viscosity decreases again in
the turbid region, and then rises approximately six orders of magnitude above the water viscosity. This second rising is due to the formation
of the liquid crystalline MLV phase.

badboy0504

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chutianshu

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