The most common misuse is the term “thixo”, or thixotropic, meaning an isothermal change in viscosity at constant shear. These two terms are often used interchangeably in the industry, though this is technically not a correct usage. The term thixotropic is used for a time-dependent shear thinning behavior at constant temperature. This would not be a desirable viscosity behavior for coatings circulated through high shear pumps. The opposite of pseudoplastic is dilatant which means that the viscosity increases with increasing shear. Pseudoplastic, simply, means that the viscosity of the material decreases (at constant temperature) with increasing shear, thus the common term shear thinning is often used. For the waterborne non-Newtonian coatings, the important terms you should keep in mind are pseudoplastic and thixotropic. So while water is a good approximate example of a Newtonian fluid, the formulated waterborne coatings display a high amount of non-Newtonian behavior. ![]() ![]() Newtonian fluids, like water for example, have a proportional relationship of shear stress and shear rate, meaning the measured viscosity is constant over the measured shear range. This fluid behavior is named after Sir Issac Newton (1642-1727) who first described viscosity as the ratio of the shear stress to the shear rate.
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