FEATURES OF RHEOLOGY OF AGAR-AGAR SOLUTIONS

Abstract

The article presents the results of experiments on studying of rheological behaviour of dilute solutions of agar-agar. The chosen range of concentration 0,1–0,7% allows to avoid gelation at ambient temperature. Dependence of viscosity and shear stress on concentration, shearing speed and temperature in an interval 25–45 °С is investigated. It was found that the concentration dependence of viscosity severely depends  on the shear speed, a nonlinearity is observed that increases with decreasing shear speed. The dependence of the viscosity on the shear speed for concentrations of 0,3–0,7% has a similar but gradually changing type of the asymptotic decrease, whereas for 0,1%, solution dependence linearly grows with increase of shear speed. The interrelation of viscosity and shear stress is studied. Curves for solutions of 0,3–0,7% have a similar type and differ significantly from curves for 0,1% solutions. Moreover, the dependencies are not typical for polymer solutions. The activation energy of viscosity and shear stress is studied. For two temperature intervals: 25–35 and 35–45 °C, there is no correlation and a smooth dependence of the measured parameters on temperature. The activation energy of both viscosity and shear stress not decreases with temperature increase, as one might expect, but increases, for many times. This fact is observed completely individually for the different concentrations. An explanation is proposed for the observed dependences, which is based on the assumption of a structural change in agar-agar solutions, which is caused by changing the concentration of solution and magnitude of the mechanical influence.