The effect of naphthols and methoxynaphthalenes on the microstructure transition of cetyltrimethylammonium bromide (CTAB) micelles is studied. Although the surface activities of these two types of organic dopants are strong, methoxynaphthalenes failed to promote spherical to worm-like micellar transition and to impart viscoelasticity to the aqueous CTAB solution, presumably due to their inability to form unique H-bonds with interfacial water. The micropolarity of OH sites of micelle-embedded naphthols is measured by observing the pK(a) shift at the micellar surface relative to bulk water. On the basis of spectroscopic and other data, the microstructures formed by both classes of dopants at the micellar surface are predicted. On the basis of hydroxyaromatic dopants, a simple and effective route to design pH-responsive viscoelastic worm-like micelles and the vesicles of single tail cationic surfactant (CTAB) is reported. Results are confirmed by observing cryogenic transmission electron microscopy (cryo-TEM) images.

Effect of 1 and 2-naphthols on the shape transition of cetyl trimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) micelles are studied. Stimuli-responsive viscoelastic gels of long wormlike micelles are formed at low surfactant concentrations in the presence of neutral naphthols, where H-bonding plays a key role in micellar shape transition in the absence of any charge screening. Micelle-embedded naphthols also act as novel self-fluorescence probes for monitoring viscoelasticity of the system as a function of applied shear. 1H NMR study shows that the solubilization sites of naphthols in the micelle are located near the surface. While UV absorption and Fourier transform infrared studies confirm the presence of intermolecular H-bonds in micelle embedded naphthols, transmission electron micrographs of vacuum-dried samples at room temperature demonstrate the transition in shape from sphere to rodlike micelles.

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The lithium, potassium, and ammonium salts of dodecylbenzenesulphonic acid have been prepared from the pure sodium salt by applying ion-exchange technique. The critical micellization concentrations (CMC) of the surfactants with four different counterions have been determined in a temperature range of 10 C to 40 C using surface tension as well as electrical conductivity measurements. The counterion ionization constant, a, and various thermodynamic parameters of micellization viz, DG 0 m , DH 0 m , DS 0 m , D mic C 0 p along with the surface parameters (C max , A min ) in aqueous media have been determined. The CMC value of dodecylbenzenesulphonate (DBS) having different counterions followed the order Na þ > Li þ > NH þ 4 > K þ . While large negative free energy change ðDG 0 m Þ and the positive entropy change ðDS 0 m Þ favor the micellization process thermodynamically, nature of their variation with counterion supports the importance of hydrated counterion size factor in micellization process via a change in the hydrophilicity of surfactant head group along with the structure of branched chain of hydrocarbon tail.

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