Effect of carbon chain length of cosurfactant on the rheological properties of nonionic wormlike micellar solutions formed by a sugar surfactant and monohydroxy alcohols

The effect of carbon chain length of monohydroxy alcohols on the rheological properties of micellar solutions formed in water/sucrose monohexadecanoate (C16SE)/monohydroxy alcohol systems (C3–C9) was studied. By adding alcohols in the aqueous C16SE solution, the zero-shear viscosity increases, and then decreases after a maximum for all the systems except for the 1-propanol system. The maximum η0 increases with the chain length of the alcohol. The oscillatory-shear behavior of the viscous samples can be described by the Maxwell model which is typically observed for wormlike micellar solutions. The plateau modulus (G0) related to the number of entanglements between wormlike micelles increases monotonously and G0 is higher for longer-chain alcohol systems except for the nonanol system, indicating more dense network is formed. The relaxation time (τR) related to the micellar length increases and then decreases with weight fraction of alcohol. It indicates a faster stress relaxation model other than Maxwell model at high alcohol content due to the formation of branched micelles. Longer carbon chain length of alcohol gives higher maximum τR. The weight fraction of alcohol at which the maximum τR appears almost corresponds to that for η0.