Structure and dynamics of aqueous mixtures of an anionic cellulose derivative and anionic or cationic surfactants

Turbidity, small-angle neutron scattering (SANS), rheology, and dynamic light scattering measurements have been carried out on aqueous semidilute anionic hydroxyethylcellulose (HEC(−)) and its uncharged analogue (HEC(0)) in the presence of an anionic surfactant (SDS) or a cationic surfactant (CTAB or Gemini(+)). Weak interactions between HEC(−) and the like-charged SDS is observed, whereas prominent electrostatic attractions between the polyelectrolyte and the oppositely charged surfactants drive the association behavior for these systems. Turbidity experiments and SANS measurements on aqueous semidilute solutions of the HEC(−) with a cationic surfactant (CTAB or Gemini(+)) reveal the formation of large polymer–surfactant association complexes as the surfactant concentration increases. The dynamic light scattering measurements also disclose pronounced interactions between HEC(−) and the oppositely charged surfactants and the formation of association complexes. The relaxation process is bimodal, and the slow mode becomes very dominant in mixtures of HEC(−)/CTAB and HEC(−)/Gemini(+). The SANS results at high q values suggest that the polymer chains are locally stretched. The q dependence of the reduced intensity from light scattering measurements on semidilute solutions of HEC(0) and HEC(−) indicate the formation of compact structures.