Interactions between the nonionic surfactant and polyacrylamide studied by light scattering and viscometry
Section snippets
Background
The interaction between polymers and surfactants was the subject of intense research effort, because of both fundamental and technological interest. Understanding of polymer–surfactant interactions is relevant to important industrial and biological processes, for example, polymers and surfactants are used conjointly in enhanced oil recovery [1]. In addition, polymer–surfactant systems are widely used in cosmetics formulations, in the food industry and in paints [2]. Most studies in this field
Materials
Two different molecular weights of polyacrylamide (PAM) [PS-19901=7×105Mw, PS-02806=5×106Mw] were obtained from Polysciences Inc. Commercial grade Triton X-100 (TX-100) was used as a nonionic surfactant, obtained from Union Carbide, Thailand Ltd. Each material was used without further purification. Sterile water was purchased from Thai Pharmaceutical Organization. Before use in light scattering experiments, it was filtered through 0.2 μm Millipore membrane filters. Analytical grade sodium azide
Binary systems
Fig. 1(a)shows a typical DLS relaxation time distribution at scattering angle θ=90° for PAM (7×105Mw) in water at 30°C at a concentration of 0.4 g l−1. This analysis indicates a bimodal distribution. The fast mode is presumed to be because of internal relaxation of polymer chains. The slow mode corresponds to center of mass diffusion. Plots of the translational diffusion coefficient vs. concentration for two different molecular weights are shown in Fig. 1(b). The diffusion virial coefficient, kD,
Conclusions
In the solutions of PAM containing sufficiently low concentrations of Triton X-100, both Rh and specific viscosity are independent of surfactant concentration. This indicates that no interaction between PAM and Triton X-100 occurs. Most of the surfactant molecules exist freely in the form of monomers. At higher concentrations the surfactant molecules induce a significant increase in the size of the polymer chains. This chain expansion occurs over a narrow Triton X-100 concentration range of
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