Definition
Substances added to a fluid or paste so that it stays thick when undisturbed but becomes thinner and flows easily when stirred, shaken, or brushed. Once the agitation stops, the material gradually returns to its thicker state.
Plain English
Additives that make a liquid behave like a thick gel when sitting still, but turn runny and easy to apply when you start working it. As soon as you stop, it stiffens up again.
Context Anchor
Seen in aircraft maintenance when working with composite repair materials, sealants, adhesives, and coatings, especially on vertical or overhead surfaces.
Derivation
From Greek thixis (touching) and trope (turning or change). The name literally means 'changes when touched,' which captures the behaviour: the material changes consistency as soon as it is worked.
Why Pilots Care
Thixotropic behaviour is why a properly mixed paint or sealant can be brushed on smoothly without running off vertical surfaces, and why some greases stay in place on a part until movement starts. Knowing the agent is thixotropic tells the technician to stir or work the product before applying it.
Analogy
Similar to ketchup in a glass bottle: thick and stuck until you shake or tap it, then it pours, then it thickens again at rest.
Intuition Check
Thixotropic does not simply mean “thick.” It means the material becomes easier to move when worked and thickens again when left alone.
Example Sentence 1
The technician stirred the sealant thoroughly because the thixotropic agents in it caused it to stiffen while sitting on the shelf.
Example Sentence 2
Because of the thixotropic agents, the sealant stayed in place on the vertical surface of the wing structure.