Thixotropic Polymer

This orange, mysterious substance feels runny and liquid when you stir it or shake its container, but becomes more solid or viscous when left alone. That’s because it has the property of thixotropy, or shear thinning, which is time-dependent. This means that the viscosity (how runny or thick it is) changes depending on the size and speed of an applied force. The effect arises because weak bonds exist between the long, chain-like polymer molecules in this material. Applying a shear stress, for example by pouring, shaking or stirring the substance, breaks these bonds. Without the strengthening brought by the bonds to the molecular polymer network, the molecules are able to slip and slide over one another more easily, making it behave more like a liquid. Thixotropy can be a very useful materials property, for example it allows ketchup to escape from glass bottles when shaken, and for paint to be applied to vertical walls without it later dripping. Other well-known thixotropic liquids include yogurt and liquid concrete.