thixotrophic

Thixotropy is a time-dependent rheological behavior where a fluid's viscosity decreases over time when subjected to mechanical stress, such as stirring or shaking, and then gradually recovers its original viscosity when the stress is removed. This phenomenon is characteristic of certain non-Newtonian fluids, meaning their flow properties are not simply proportional to the applied stress.

Materials exhibiting thixotropy typically have a complex internal structure that breaks down under agitation. This breakdown reduces the resistance to flow, making the material appear thinner or more fluid. Once the stress is removed, the internal structure slowly reforms, and the material thickens again. The rate at which the viscosity decreases and recovers depends on the specific material and the conditions, such as temperature and the magnitude of the applied stress.

Examples of thixotropic substances include certain paints, inks, gels, and some food products like ketchup and yogurt. In paints, thixotropy allows them to be easily brushed or sprayed (low viscosity under stress) but prevents them from dripping or sagging once applied (higher viscosity when stress is removed). Similarly, ketchup flows more easily when shaken or squeezed but thickens again in the bottle. The study of thixotropy is important in various industries for controlling the application and performance of these materials.