On the methodological features and errors of measuring the surface tension of aqueous suspensions

The paper analyzes the methodological features of measuring the surface tension of highly dispersed systems, which include bentonite suspensions. It is shown that bentonite suspensions are complex nonequilibrium systems, when measuring the surface tension of which it is necessary to take into account the influence on its value of many factors, the main ones being dispersion and sedimentation. These factors have a significant effect on the measured value of surface tension. The non-equilibrium of the system under study leads to a time dependence of the surface tension, which significantly complicates the measurement of its dependence on temperature. To measure the surface tension of a bentonite suspension, a new method based on the superposition of measurement results obtained by two independent methods, the hanging drop method and the lying drop method, has been developed and tested. Sedimentation, when using these methods, leads to oppositely directed (relative to the surface) processes: in the first case, the surface of the drop enriches the particles of the solid phase, in the second – is impoverished. Experimental studies of the time dependences of surface tension have shown that in the hanging drop method there is a linear decrease in surface tension, in the lying drop method the surface tension increases linearly with time. Superposition of the results obtained by these methods allows us to find the value of surface tension at a given time. An analysis of surface tension measurement errors of the influence of various factors on the error in measuring surface tension of the developed method is carried out.