STUDY OF THE VISCOSITY OF NONIONIC SURFACTANT DEUTERIUM-OXIDE MIXTURES AND OF THE SELF-DIFFUSION COEFFICIENT OF THE SURFACTANT APPROACHING THE LIQUID LIQUID COEXISTENCE CURVE/

Plots of the temperature dependence of the shear viscosity eta of C12E 5/D2O mixtures with compositions in the range 0.60 x 10(-2) < y < 10.0 8 x 10(-2) (critical composition y(c) = 1.08 x 10(-2); y, mass fractio n of C12E5) are S-formed (a shallow minimum at a lower temperature T-e ta min and a maximum at a higher temperature T-eta max). The measureme nts are carried out in the temperature range 5 degrees C < T < T-P;T-P approximate to 30 degrees C approaching the lower part of the binodal curve (Tp, temperature of phase separation of the mixture). In the te mperature range (T-P - T-eta max) the viscosity decreases with increas ing temperatures. At compositions y < 0.60 x 10(-2) the viscosity decr eases with increasing temperature monotonically. The self-diffusion co efficient of C12E5 in C12E5/D2O mixtures is measured in the same tempe rature and composition range. The findings of both types of experiment s are rationalized in terms of a model developed by Nilsson et al. (J. Phys. Chem. 1983, 87, 1377). The results give support to the hypothes is that the characteristic features of the temperature and composition dependence of both transport coefficients in the large aggregate regi on of the phase diagram have a common cause: The structural dynamics o f the large micellar aggregates increases approaching the liquid/liqui d coexistence curve at compositions y > y(c). Concentration fluctuatio ns with long range correlations appear to be involved in this process.