Novel Viscoelastic Systems from Azobenzene Dye and Cationic Surfactant Binary Mixtures: Effect of Surfactant Chain Length

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Abstract
Sodium 4-[(E)-phenyldiazenyl] benzoate (AZONa), a photo-responsive dye, induced micellar growth in alkyl-trimethylammonium bromide (dodecyl-, DTAB; tetradecyl-, TTAB; cetyl-, CTAB and octadecyl-, OTAB) solutions was investigated using light scattering and viscosity. The viscosity decrease upon increasing [surfactant] to above about 20 mM was found to be common from TTAB to OTAB solutions at fixed mole ratio of [AZONa]/[surfactant]. Cryo-TEM demonstrated that the decrease of viscosity was attributed to the entangled linear to multi-connected saturated network wormlike micelles transition. UV-vis spectra showed that AZONa interacted strongly with OTAB as revealed from both the shifting of absorbance peak and the variation of absorbance intensity, which suggest the binding of AZONa to OTAB micelles. 1H NMR confirmed the solubilization of AZONa to the palisade layer and growth of micelles upon increasing [AZONa] as revealed from the shifting and broadening of peaks.

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