Interactions between a chemically cross-linked poly(N-isopropylacrylamide) (PNIPAAM) microgel and the anionic surfactant sodium dodecyl sulfate (SDS) have been investigated by dynamic light scattering (DLS) and turbidimetry in both a buffer system (pH = 7) with an ionic strength of 0.05 M and water. Both the turbidity and DLS measurements revealed significant polymer-surfactant interactions between PNIPAAM and SDS in the buffer system, whereas in the absence of buffer only the highest SDS concentration clearly deviates from what is observed in the absence of surfactant. The DLS results show that the particles shrink with increasing temperature at all conditions; a macroscopic phase separation is approached at higher temperatures for the microgels without or with low SDS concentration in the buffer system. Mixtures of microgels and surfactants may be promising for enhanced oil recovery applications.

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