thixotrópia

Thixotropy is a property of certain materials that exhibit a reversible change in viscosity when subjected to stress. This means that the material flows more easily under stress and becomes more viscous when the stress is removed. The term "thixotropy" comes from the Greek words "thixis," meaning "to press," and "tropos," meaning "change."

Materials that exhibit thixotropic behavior include some types of gels, suspensions, and emulsions. For example, a thixotropic material might flow like a liquid when shaken or stirred but return to a gel-like state when left undisturbed. This property is often desirable in applications such as paints, cosmetics, and food products, where a material needs to be easily spreadable but also stable and non-dripping when not in use.

The thixotropic behavior of a material is typically characterized by its yield stress, which is the minimum stress required to initiate flow. Below this yield stress, the material behaves like a solid, while above it, it flows like a liquid. The time-dependent nature of thixotropy means that the material's viscosity can change over time under constant stress, making it a dynamic property.

Thixotropy is distinct from rheopexy, another time-dependent rheological property, where the material's viscosity increases over time under constant stress. Understanding thixotropic behavior is crucial in various industries for optimizing product performance and stability.