ABSTRACT
We have investigated the phase diagram of the triblock copolymer P123 solved in water by viscosity measurements for different concentrations and temperatures. The structures of the different phases were identified by surface sensitive neutron diffraction. We find a pronounced hysteresis between heating and cooling. During heating, a highly viscous crystalline fcc phase is found before melting occurs at 44 °C with a simultaneous drop in viscosity. Upon cooling, first a hexagonal phase with low viscosity develops followed by a highly viscous fcc phase. Phase diagrams for the heating and cooling cycle for different concentrations are provided. The hysteric behavior is discussed in relation to the shape of the micelles.
ABSTRACT
A 20% aqueous solution of (ethylene oxide) 99-(propylene oxide) 65-(ethylene oxide) 99, F127, was investigated by combining rheology in a cone/plate-geometry and surface-sensitive grazing incident neutron scattering. The crystalline structure formed by the polymer micelles becomes less pronounced for low shear rates, but correlations increase for higher shear rates. After stopping shear a slow relaxation of the micelles is found in the vicinity (50 mum thick layer) of a hydrophilic silicon wall (strong micelle-wall interaction), while a fast relaxation is observed in the boundary layer against the hydrophobic silicon wall (weak micelle-wall interaction). The results show that in the vicinity of the interface wall-particle interactions compete heavily with the shear force acting on the liquid.
