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| - Polymer−Surfactant Interactions in Dilute Mixtures of aNonionic Cellulose Derivative and an Anionic Surfactant
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| - The interaction between ethyl(hydroxyethyl)cellulose (EHEC) and the anionic surfactant sodium dodecylsulfate (SDS) has been studied in dilute aqueous solutions at different temperatures with the aid ofviscometry. The results suggest that at low polymer concentrations the polymer−surfactant complexes aremolecularly dispersed at the shear rates operating in the capillary viscometers used in this study. Thedelicate interplay between hydrophobic interactions and polyelectrolyte effects is demonstrated throughthe reduced viscosity data. At surfactant concentrations slightly above the critical aggregation concentrationcac (the value of cac decreases with increasing temperature), the intrinsic viscosity features suggest asharp collapse of the polymer−surfactant aggregates. At moderate amounts of surfactant, the molecularcomplexes expand due to amended thermodynamic conditions and enhanced electrostatic repulsion betweenchains decorated with SDS. At very high levels of surfactant addition, the small contraction of the molecularunits is attributed to screening of the electrostatic interactions. At low surfactant concentrations (up to4 mm), a temperature-induced shrinkage of the molecules is also observed. The very high values of theHuggins coefficient around cac suggest strong coil−coil interactions. The polymer-concentration-inducedenhancement of the reduced viscosity around the cac is another indication of enhanced intermolecularinteractions.
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