Rheological Properties of Wormlike Micellar Solutions Being Available in Wide Temperature Range in Sucrose Palmitate Systems

摘要

We investigated the melting point of the hydrated solid and rheological property of wormlike micellar solutions in the water/sucrose monopalmitate (C_(16)SE)/tri (oxyethylene) dodecyl ether (C_(12)EO_3) system when a part of C_(16)SE was substituted with the surfactants which have lower Krafft point than C_(16)SE. The melting point of the hydrated solid of the water/C_(16)SE/C_(12)EO_3 system is around 34℃. When C_(16)SE is substituted with sodium dodecyl sulfate (SDS), the melting point of the hydrated solid decreases below 5℃ at α (weight fraction of SDS in C_(16)SE+SDS mixture) being greater than 0.3 and the zero shear viscosity (η_0) increases from the original nonionic system. When C_(16)SE is substituted with octa (oxyethylene) dodecyl ether (C_(12)EO_8), the melting point of the hydrated solid decreases down to 24℃ and the maximum zero shear viscosity (η_0~(max)) decreases with the increase in α (weight fraction of C_(12)EO_8 in C_(16)SE+C_(12)EO_8 mixture). η_0~(max) is dramatically increased by the substitution of C_(16)SE with SDS. With further increase of α, η_0~(max) decreases gradually. The dynamic rheology data of highly viscous wormlike micellar solutions fit well to the Maxwell's mechanical model of viscoelastic material, indicating the formation of rigid network of entangled wormlike micelles. Shear (plateau) modulus G_0 is almost unchanged, whereas relaxation time τ_R shows similar behavior to η_0~(max). Hence, the behavior of η_0~(max) can be explained from the behavior of τ_R by considering the equation relating these quantities, η_0 = G_0τ_R. Since τ_R is proportional to the length of wormlike micelles, the behavior of η_0~(max) can be explained in terms of the change in the length of wormlike micelles caused by the addition of SDS.