Celeste Biever in New Scientist:
A burst of high-frequency sound waves is enough to turn a range of oily liquid mixtures to jelly. Because the reaction is reversible, it could be used to remotely control the viscosity of liquid shock absorbers in cars or of lubricants in robotic joints, or to temporarily solidify fuels and paints so they don’t leak during transport. Engineers may one day even use the technology to make building dampers that absorb energy from external forces, prolonging a structure’s life and preventing a catastrophic event such as an earthquake from destroying it.
Gels are semi-solid mixtures that consist of a liquid trapped within the pores of a continuous network of chain-like molecules. They are usually created by adding an acid to a liquid with a solid suspended in it, known as a sol, or illuminating a sol with a flash of UV light.