The combination of cornstarch and water forms a thixotropic fluid.
Thixotropy is a property exhibited by some fluids which have a jelly-like consistency when stationary, but which dilute when subjected to shear stresses. One of the classic examples of a thixotropic fluid is quicksand. As long as it is not disturbed, the sand will be relatively coarse. Once something falls and starts thrashing around, putting pressure on quicksand, it becomes more liquid. In addition to being a concern for people who fall into quicksand pits, thixotropy is a property that can be put to use in a number of interesting ways.
Quicksand is a classic example of a thixotropic fluid.
A thixotropic fluid will become less and less viscous as it is subjected to stresses such as shaking, shaking, or shaking. Once the deformation stops, the fluid will regain its viscosity, slowly returning to a semi-solid state. This is in contrast to a rheopectic fluid, which will experience an increase in viscosity as it is stirred; a mixture of cornstarch and water, for example, will be gelatinous on standing, but will be firm under pressure. The “gloop” of cornstarch and water is sometimes used in science classes to introduce students to the concept with a fluid they can feel and manipulate.
The thixotropy characteristics of drilling fluids require special techniques, including the use of shale shakers, to separate large solids.
Engineers need to think about thixotropy when designing structures because some substrates can be thixotropic. For example, when engineers build structures on reclaimed land, the clays underneath can be subject to liquefaction during an earthquake, posing a safety hazard. While it is possible to build on clays and thixotropic soils, care must be taken for safety, with the structure being anchored in a substrate that will not liquefy during deformation, such as bedrock.
Drilling fluids used in the oil and gas industry can also be thixotropic in nature. The fluids will remain relatively solid when standing still, but will liquefy as they are used during drilling to act as lubricants. Thixotropy is also of interest to people working with clays, such as potters, and in some areas of the food industry. Some foods have properties such as thixotropy, which can interfere with the way they are handled and processed.
Engineers who study fluid mechanics have several explanations for how thixotropy works, depending on the fluid involved and the types of forces it is subjected to. Understanding this property can be important for people working with thixotropic fluids, as it will allow them to predict the behavior of the fluid and explore the ways in which this property can be harnessed.