Antithixotropic fluids

Rheopectic (antithixotropic) fluids are shear-thickening fluids whose r a increases with time under constant or low y. Rheopexy is a property of linear... 

Cheng, D. C. H., and Evans, F. (1965). Phenomenological characterization of the rheological behavior of inelastic reversible thixotropic and antithixotropic fluid. Br. J. Appl. Phys. 16, 1599-1617. 

When the shear stress changes in Newtonian, dilatant, or pseudoplastic liquids, as well as in Bingham bodies or fluids above the flow limit, the corresponding shear gradient or the corresponding viscosity is reached almost instantaneously. In some liquids, however, a noticeable induction time is necessary, i.e., the viscosity also depends on time. If, at a constant shear stress or constant shear gradient, the viscosity falls as the time increases, then the liquid is termed thixotropic. Liquids are termed rheopectic or antithixotropic, on the other hand, when the apparent viscosity increases with time. Thixotropy is interpreted as a time-dependent collapse of ordered structures. A clear molecular picture for rheopexy is not available. 

There are several terms that apply to time-dependent behavior. Thixotropic fluids possess a structure that breaks down as a function of time and shear rate. Tlius the viscosity is lowered. A famous example of this reversible phenomenon is the ubiquitous catsup bottle, yielding its contents only after sharp blows. The opposite effect, although rarely observed, is called antithixotropic, or rheopectic behavior, where materials set up as a function of time and shear rate that is, the viscosity increases or the material gels. 

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