We investigated the melting point of the hydrated solid and rheological property of wormlike micellar solutions in the water/sucrose monopalmitate (C
16SE)/tri (oxyethylene) dodecyl ether (C
12EO
3) system when a part of C
16SE was substituted with the surfactants which have lower Krafft point than C
16SE. The melting point of the hydrated solid of the water/C
16SE/C
12EO
3 system is around 34°C. When C
16SE is substituted with sodium dodecyl sulfate (SDS), the melting point of the hydrated solid decreases below 5°C at α (weight fraction of SDS in C
16SE+SDS mixture) being greater than 0.3 and the zero shear viscosity (η
0) increases from the original nonionic system. When C
16SE is substituted with octa (oxyethylene) dodecyl ether (C
12EO
8), the melting point of the hydrated solid decreases down to 24°C and the maximum zero shear viscosity (η
0max) decreases with the increase in α (weight fraction of C
12EO
8 in C
16SE+C
12EO
8 mixture). η
0max is dramatically increased by the substitution of C
16SE with SDS. With further increase of α, η
0max 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
G0 is almost unchanged, whereas relaxation time τ
R shows similar behavior to η
0max. Hence, the behavior of η
0max 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
0max can be explained in terms of the change in the length of wormlike micelles caused by the addition of SDS.
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