GENERALIZED METHOD FOR NORMALIZING THE DEGREE OF THIXOTROPY/RHEOPEXY FOR TO EVALUATE THE STRUCTURE OF POWDER SUSPENSIONS 

Abstract

The structure of suspensions used to form films by colloidal methods determines their main properties: thickness, surface roughness, and density. Studying the structure of liquid suspensions by direct methods is significantly complicated, especially when the task is to determine changes in the structure induced by mechanical loads that occur during the formation of films. This problem can be solved through rheological studies. For this purpose, a method for normalizing the degree of thixotropy/rheopexy was developed for use as a quantitative parameter for evaluating the structure of a liquid based on its rheological properties. The trapezoidal integration method for calculating the flow curve area was demonstrated. The developed normalization method relies on a modified standard score equation, taking into account the peculiarities of the flow curves. The normalized thixotropy/rheopexy degree was used to analyze the structures of suspensions of the same composition, whose flow curves were plotted with application of different maximum shear rates (200, 500, and 800 sec^-1). The nonnormalized thixotropy degrees for the studied suspensions differed by 11 to 12 times. The developed parameter allowed the deviation to be reduced to 16–19%. The normalized degree of thixotropy/rheopexy, along with the flow coefficient and effective viscosity, was used for the indirect assessment of changes in the suspension structure with an increase in the nanopowder content based on the rheological properties. This approach enabled recording of four structural states of the suspension: separated agglomerates, increase in the sizes of the agglomerated accompanied by rheopexy flow, transition to the Newtonian flow after the deformation of the agglomerates in the direction of the flow, and formation of a regular network structure as evidenced by the recording of the thixotropic flow.