Elsevier

Polymer

Volume 40, Issue 21, October 1999, Pages 5741-5749
Polymer

Interactions between the nonionic surfactant and polyacrylamide studied by light scattering and viscometry

https://doi.org/10.1016/S0032-3861(98)00811-8Get rights and content

Abstract

Light scattering and viscometric measurements were made on ternary mixtures of high molecular weight polyacrylamide (PAM), and the nonionic surfactant, Triton X-100 (TX-100) in aqueous solution. The binary solutions of polymer and surfactant in aqueous media were also studied. In the ternary system, the solution viscosity and translational diffusion coefficients were determined at 30°C in terms of (a) the surfactant concentration at fixed PAM concentration, (b) the PAM concentration at fixed surfactant concentration, and (c) the PAM molecular weight. The surfactant concentration was varied by five orders of magnitude, the mean diffusion coefficient decreased slightly at first until reaching a minimum and then rose toward an asymptotic value which was identical to that of a single micelle. Near the cmc, the binding of the surfactant onto a polymer chain induced a slight chain expansion, but surprisingly the specific viscosity diminished. DLS shows a component owing to free micelle diffusion at concentrations above 1 mM of TX-100. This indicates the saturation point of binding between PAM and TX-100. Different molecular weights of PAM interacted with the surfactant quite similarly.

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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