Determination of the rheological properties of aqueous solutions of branched PEO-PPO-PEO copolymers. Confrontation with small-angle neutron scattering studies.

The physico-chemical properties of Tetronic (R) 908 in aqueous solution hav e been explored on a wide range of temperature and concentration. This syst em presents interesting theological properties depending on the polymer con centration in solution, and temperature. For weight percentage p comprised between 5% and 20%, the viscosity of the solution passes through a maximum Small angle neutron scattering experiments show that the increase in the vi scosity is due to the progressive aggregation of the chains. For higher wei ght percentages, the viscosity of the system diverges and the mixture becom es "gel-like". SANS studies of the same solution indicate that the micelles are organized in a cubic structure. We have developed a model which suitab ly describes the SANS curves of the system in the region where micelles are formed. It allows the calculation of several parameters (volume fraction o f the micelles, size, composition). The evolution of these parameters with temperature and polymer concentration is detailed. Comparisons with models of literature are discussed.