A series of model hydrophobically end-capped poly(ethylene oxide) derivatives was prepared in which the molecular weight of the main chain ranged between 2000 and 35000 and with paraffinic extremities of 12 or 18 carbon atoms. The structure of the aqueous solutions of these polymers was investigated by neutron and X-ray scattering techniques in the whole range of composition. Phase diagrams were deduced from these studies and complementary differential scanning calorimetry measurements. They exhibit (i) several monophasic domains corresponding to a homogeneous dispersed solution, a micellar solution and a micellar cubic phase, and (ii) several biphasic domains corresponding to a demixing between a lamellar and a cubic phase at higher polymer concentration and a demixing between a dispersed solution and a micellar solution, at lower polymer concentration. The micellar solutions are locally organized in a cubic array and correspond to a classical associative behavior. Transitions from the micellar solutions to the cubic phase are observed when temperature and molecular weight decrease. Both phases are compatible with the formation of micelle-like hydrophobic micro-domains of spherical shape whose radius increases with concentration. The average distance d between the micelles decreases when concentration increases. d is larger than the end to end distance of the PEO chain at low concentration and for high molecular weight and tends, at higher concentration, toward the same value for all the polymers, when plotted vs. the hydrophobic content. The concentration dependence of the viscosity was studied in the micellar solution domain for two different polymers. Important differences are observed between polymers of the same molecular weight bearing end groups of 12 or 18 carbon atoms. Several concentration regimes can be distinguished. These solutions are mainly shear-thinning and the shear rate threshold is much higher for polymers bearing C12 end groups. In a narrow range of concentration, they also exhibit a shear-thickening behavior, prior to the shear-thinning. Preliminary neutron scattering experiments were performed on solutions which exhibit Newtonian or shear-thickening and shear-thinning behaviors as a function of the shear rate. No modification of the scattering patterns was observed in the Newtonian regime. Under specific experimental conditions, a phase separation is observed during the shear-thinning step.
