thixotrophe

A thixotrope is a substance that exhibits thixotropy, a time-dependent shear thinning property. This means that the substance's viscosity decreases over time when subjected to constant shear stress. When the stress is removed, the substance gradually regains its original viscosity. This behavior is reversible.

Thixotropy is observed in a variety of materials, including some gels, paints, inks, and even certain food products. The underlying mechanism often involves the breakdown and reformation of a weakly structured network within the material under shear. For example, in some gels, particles are held together by weak physical forces, forming a three-dimensional network that gives the substance its initial viscosity. When agitated or stirred, these bonds break, causing the structure to collapse and the viscosity to drop. Upon standing, the bonds slowly reform, and the viscosity increases again.

The rate at which a thixotropic substance recovers its viscosity after shear is an important characteristic and can vary significantly between different materials. This property makes thixotropic substances useful in applications where a material needs to be easily flowable during application but then become more viscous or solid-like to maintain its shape or position. For instance, paints are formulated to be thixotropic so they can be easily brushed or rolled onto a surface but then thicken on the wall to prevent dripping. Similarly, thixotropic drilling fluids are used in the oil and gas industry; they are thin enough to be pumped down the drill hole but thicken when pumping stops, helping to suspend rock cuttings and prevent them from settling.