Addition of lipophilic polyoxyethylene dodecyl ether (C
12EO
n) to the dilute micellar solution of polyoxyethylene phytosterol (PhyEO
m m = 10 and 20) results in the increase in viscosity. The increase in viscosity is attributed to the C
12EO
n induced one-dimensional micellar growth leading to the formation of worm-like micelles. Steady and oscillatory shear rheological measurement in PhyEO
m + C
12EO
n (n = 2-5) shows that on decreasing the EO chain length of C
12EO
n, in general, the one-dimensional micellar growth becomes increasingly favorable. However, with very short EO-chain, for example, C
12EO
2, phase separation occurs at a lower concentration before significant micellar growth can be induced. In the systems of C
12EO
3 and C
12EO
4, the wormlike micelles entangle to form a viscoelastic transient network having a dynamic rheology that can be described by Maxwellian model in wide range of shear frequency. It was found that increasing the concentration or decreasing the EO-chain length of PhyEO
m in the mixed system favors one-dimensional micellar growth. Comparison of the rheological behavior of PhyEO
m + C
12EO
n systems with that of polyoxyethylene cholesterol (ChEO
m) + C
12EO
n systems at similar conditions shows that in the former system C
12EO
n can induce micellar growth more effectively, which is attributed to the additional branching of the alkyl chain in the lipophilic moiety of the amphiphile.
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