What are dilatant fluids?
Graph drawn by self
Properties
Dilatant fluids, also known as shear thickening fluids, are liquids or solutions whose viscosity increases as stress is applied [1]. They are an example of non-Newtonian fluids, as they do not have a linear shear stress versus shear rate rate, which is unique to Newtonian fluids [2] (see graph). This means that some dilatant fluids have the unique property of being able to turn from liquid to a solid just by having stress applied.
There are also such things as shear thinning fluids, or pseudoplastics, which display the opposite properties of dilatant materials; as more stress is applied to pseudoplastics the viscosity decreases (or shear rate increases)[2],
Natural non-Newtonian fluids
A number of non-Newtonian fluids can be found naturally, although most of them are pseudoplastics as opposed to dilatants. A famous example of a non-Newtonian fluid is quicksand. At first it seems solid but as the victim walks onto it, thereby applying stress and causing it to become more viscous (as quicksand is a pseudoplastic), they sink in as they struggle, applying more stress to the quicksand, which then thins causes them to sink faster. Another example of a pseudoplastic is ketchup, which will not flow until it is squeezed or shaken [3].
There are not as many natural dilatants, although certain proportions of sand and water mixed together can display dilatant properties. For example at a beach, if you stand on the wet sand, your feet will sink in slightly, but if you run across the sand (thus applying greater stress to it), it will behave as a solid and your feet will not sink in. A dilatant fluid can easily be made by making a 2:1 mixture of cornflour and water. It is a liquid, but when stirred it becomes thicker and more difficult to stir. If hit with a hammer, it will shatter like a brittle solid; but if left it will return to a liquid[1][3].
Rheopecty
Dilatancy is not to be confused with rheopecty, even though both properties have increased viscosity as a result of applied stress. The difference between dilatant and rheopectic materials is that rheopectic materials' viscosity is time dependant and thus increases the longer the stress is applied [4][5], whereas dilatant materials' viscosity increases just with an increase in stress. An example of a substance that displays rheopecty is cream; which becomes stiff only after prolonged beating.
Click here to see why dilatant fluids have these properties?
Dilatant fluids, also known as shear thickening fluids, are liquids or solutions whose viscosity increases as stress is applied [1]. They are an example of non-Newtonian fluids, as they do not have a linear shear stress versus shear rate rate, which is unique to Newtonian fluids [2] (see graph). This means that some dilatant fluids have the unique property of being able to turn from liquid to a solid just by having stress applied.
There are also such things as shear thinning fluids, or pseudoplastics, which display the opposite properties of dilatant materials; as more stress is applied to pseudoplastics the viscosity decreases (or shear rate increases)[2],
Natural non-Newtonian fluids
A number of non-Newtonian fluids can be found naturally, although most of them are pseudoplastics as opposed to dilatants. A famous example of a non-Newtonian fluid is quicksand. At first it seems solid but as the victim walks onto it, thereby applying stress and causing it to become more viscous (as quicksand is a pseudoplastic), they sink in as they struggle, applying more stress to the quicksand, which then thins causes them to sink faster. Another example of a pseudoplastic is ketchup, which will not flow until it is squeezed or shaken [3].
There are not as many natural dilatants, although certain proportions of sand and water mixed together can display dilatant properties. For example at a beach, if you stand on the wet sand, your feet will sink in slightly, but if you run across the sand (thus applying greater stress to it), it will behave as a solid and your feet will not sink in. A dilatant fluid can easily be made by making a 2:1 mixture of cornflour and water. It is a liquid, but when stirred it becomes thicker and more difficult to stir. If hit with a hammer, it will shatter like a brittle solid; but if left it will return to a liquid[1][3].
Rheopecty
Dilatancy is not to be confused with rheopecty, even though both properties have increased viscosity as a result of applied stress. The difference between dilatant and rheopectic materials is that rheopectic materials' viscosity is time dependant and thus increases the longer the stress is applied [4][5], whereas dilatant materials' viscosity increases just with an increase in stress. An example of a substance that displays rheopecty is cream; which becomes stiff only after prolonged beating.
Click here to see why dilatant fluids have these properties?
