Physio-chemical properties of polymyxan 88A¯water system

The system exopolysaccharide polymyxan 88A¯water was studied at several temperatures. The temperature dependence of viscosity at cooling and heating was obtained in order to estimate the phase separation temperature (Ts) and the gelation temperature (Tg). The experimental values of Ts and Tg were used to plot the phase diagram of the system under study at polymer concentrations below 1.5 wt%. Viscous flow in the system was examined by the cylinder¯cylinder rotation method. It has been found that: (i) at shear rates within 1¯100 s-1 the dependence of viscosity on shear rate can be fairly expressed by the power low; (ii) the activation enthalpy of viscous flow practically does not depend on shear rate; and (iii) the activation entropy of viscous flow is negative, most likely due to an orienting action of mechanical field.