Anti-thixotropy

Time Effects during Flow Thixotropy and Negative (or Anti-) Thixotropy... 

The above changes are accompanied with s decrease or increase of viscosity with time at any given shear rate. These changes are referred to as thixotropy if the viscosity decreases with time, or as negative thixotropy or anti-thixotropy if the viscosity increases with time. 

Microstructural theories of suspensions appear to be particularly well suited to solve problems associated with time-dependent flows, thixotropy and rheopexy (anti-thixotropy) [Russel, 1983 Utracki, 1989, 1995]. 

This studies have shown that the rheological parameters are affected by the type of measuring device, composition of the paste and rheological history of the sample. The pastes can be attributed to the Newtonian or non-Newtonian types of liquid between the later the plastic (Bingham), pseudo-plastic or exhibiting the dilatancy phenomena can be differentiated. Moreover, the pastes reveal basically the thixotropy or anti-thixotropy properties. 

Two types of flow are recognized thixotropy, defined as a decrease of apparent viscosity under shear stress, followed by a gradual recovery when the stress is removed, and its opposite, anti-thixotropy, or rheopexy. Both are related to molecular or macroscopic changes in interactions. In thixotropic liquids, the aggregate bonding must be weak enough to be broken by flow-induced hydrodynamic forces. If dispersion is fine, even slight interactions may produce thixotropic effects. When... 

In fluids with time-dependent behavior, the effects of time can be either reversible or irreversible. If the time effects are reversible, the fluids are either thixotropic or rheopectic. Thixotropy is the continuous decrease of apparent viscosity with time under shear and the subsequent recovery of viscosity when the flow is discontinued. Rheopexy is the continuous increase of apparent viscosity with time under shear it is also described by the term anti-thixotropy. A good review on thixotropy was given by Mewis [45]. Polymer melts do exhibit some thixotropic effects however, thixotropy can also occur in inelastic fluids. The time scale of thixotropy is not necessarily associated with the time scale for viscoelastic relaxation. 

In industrial products, the use of fumed silica will confer thixotropy, sag resistance, particle suspension, emulsifiability, reinforcement, gloss reduction, flow enhancement of powders, anti-caking, anti-slip, anti-blocking, etc. Because of its effect on these important properties, fumed silica is widely used in many industries. 

Impart thickening/thixotropy, flow control, anti-sag and reinforcement to acrylic, polymethane, polyvinyl plastisols, styrene butadiene rubber and latexes... 

---