Rheological properties of wormlike micellar solutions being available in wide temperature range in sucrose palmitate...

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 degrees C. When C(16)SE is substituted with sodium dodecyl sulfate (SDS), the melting point of the hydrated solid decreases below 5 degrees C at alpha (weight fraction of SDS in C(16)SE+SDS mixture) being greater than 0.3 and the zero shear viscosity (eta(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 degrees C and the maximum zero shear viscosity (eta(0)(max)) decreases with the increase in alpha (weight fraction of C(12)EO(8) in C(16)SE+C(12)EO(8) mixture). eta(0)(max) is dramatically increased by the substitution of C(16)SE with SDS. With further increase of alpha, eta(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 tau(R) shows similar behavior to eta(0)(max). Hence, the behavior of eta(0)(max) can be explained from the behavior of tau(R) by considering the equation relating these quantities, eta(0)=G(0)tau(R). Since tau(R) is proportional to the length of wormlike micelles, the behavior of eta(0)(max) can be explained in terms of the change in the length of wormlike micelles caused by the addition of SDS.