Rheological behavior in water of complexes formed from poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) and positively charged rodlike micelles

The viscoelastic behavior of aqueous solutions of an ionic complex formed from poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) and rodlike mixed micelles of dimethyloleylamine oxide (DMOAO) and hexadecyltrimethylammonium chloride (CTAC) was investigated under oscillatory conditions. The DMOAO/CTAC mixed micelles exhibited high zero-shear viscosities (η0) depending on the mole fraction of CTAC in the mixed micelle (Y) in the range 0⩽Y⩽0.25. The addition of the polyanion had no effect on the rheological behavior of the mixed micelles when Y<0.02 at an ionic strength (μ) of 0.2. However, when Y was increased to a certain level (Yc), η0 decreased drastically; Yc depended on μ but not on the polymer concentration. These observations indicate the formation of an ionic complex between the polymer and micelle when Y⩾Yc. The reciprocal of steady-state compliance (Je−1) began to decrease gradually at Y≈Yc and then leveled off at Y>0.06. The relaxation time (τ) was found to be more strongly dependent on Y. Thus, the large decrease in η0 was attributed mainly to a decrease in τ while the number density of junctions decreased only slightly. Therefore, it is concluded that polymer-micelle complex maintains a rodlike structure with some entanglements remaining at Y<0.12.