Wormlike micelles in Tween-80/CmEO3 mixed nonionic surfactant systems in aqueous media

Formation and rheological behaviour of viscoelastic wormlike micellar solution in aqueous mixed system of nonionic surfactants, polyoxyethylene sorbitan monooleate (Tween-80) and trioxyethylene alkyl ether (CmEO3, m=12m=12, 14, and 16) was studied. The semi-dilute aqueous solution of Tween-80, in presence of CmEO3 shows a sharp increase in viscosity leading to the formation of a gel-like highly viscoelastic solution reaching a maximum, but decreases beyond an intermediate concentration and finally phase separates. When C12EO3 is replaced by C14EO3 the micellar growth occurs more effectively. However, with further increase in alkyl chain length, i.e. with C16EO3, phase separation occurs before a viscoelastic solution is formed. The effect of temperature on the water/Tween-80/C14EO3 mixed surfactant system was also studied. With increase in temperature, viscosity increases more promptly and the viscosity maximum is attained at relatively lower concentration of C14EO3. Enhanced one dimensional micellar growth with increase in the temperature is mainly attributed to the decrease in the spontaneous curvature of the aggregates. Structural investigation by means of small-angle X-ray scattering (SAXS) technique of micelles in aqueous solution of Tween-80 and mixed water/Tween-80/CmEO3 systems confirmed the one dimensional micellar growth in the above system.

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