Representation and characterization of thixotropic fluids

Thixotropy is a time-dependent rheological behavior of a group of fluids which are characterized by an isothermal reversible breakdown induced by a mechanical disturbance. Based on this definition, a mathematical model of reversible degradation kinetics is set up. Its development leads to two equations which represent quantitatively the hysteresis loop and torque-decay curve. These equations consist of five independent parameters with their physical meanings. These parameters can be used to characterize the properties of thixotropic materials. The original Weissenberg Rheogoniometer was modified to measure the thixotropic behavior of blood with the step change and the ramboid change of shear rate. The results of experimental measurements confirmed that blood is a thixotropic material. This is explained by the breakdown of rouleaus and clumps as an aggregated form of erythrocytes into single red cells as a non-aggregated form of erythrocytes. The comparison of model prediction with the experimental results shows that the model equations can quantitatively represent the behavior of bloods. Therefore the parameters determined by the experimental data are used to compare and characterize the physical-chemical properties of blood