Kaye effect

{{Short description|Property of complex liquids}}

File:The Kaye-Effect.jpg

The Kaye effect is a phenomenon observed in some complex liquids which was first described by the British engineer Alan Kaye in 1963.{{Cite journal | last1 = Kaye | first1 = A. | title = A Bouncing Liquid Stream | doi = 10.1038/1971001a0 | journal = Nature | volume = 197 | issue = 4871 | pages = 1001–1002 | year = 1963 |bibcode = 1963Natur.197.1001K | s2cid = 4265638 }}

While pouring one viscous mixture of an organic liquid onto a surface, the surface suddenly spouted an upcoming jet of liquid which merged with the downgoing one.

This phenomenon has since been discovered to be common in many non-Newtonian liquids (liquids with a shear-stress-dependent viscosity or viscoelastic properties). Common household liquids in this category are liquid hand soaps, shampoos and non-drip paint. The effect usually goes unnoticed, however, because it seldom lasts more than about 300 milliseconds. The effect can be sustained by pouring the liquid onto a slanted surface, preventing the outgoing jet from intersecting the downward one (which tends to end the effect).

Whilst it was long thought to occur due to a shear-thinning slip layer,{{Cite journal | last1 = Versluis | first1 = M. | last2 = Blom | first2 = C. | last3 = van der Meer | first3 = D. | last4 = van der Weele | first4 = K. | last5 = Lohse | first5 = D. | title = Leaping shampoo and the stable Kaye effect | doi = 10.1088/1742-5468/2006/07/P07007 | journal = Journal of Statistical Mechanics: Theory and Experiment | volume = 2006 | issue = 7 | pages = P07007 | year = 2006 | arxiv = physics/0603183 | s2cid = 119096147 }} recent studies have shown through high-speed videos{{Cite journal | last1 = Lee | first1 = S. | last2 = Li | first2 = E. | last3 = Marston | first3 = J. | last4 = Bonito | first4 = A. | last5 = Thoroddsen | first5 = S. | title = Leaping shampoo glides on a lubricating air layer | doi = 10.1103/PhysRevE.87.061001 | journal = Physical Review E | volume = 87 | issue = 6 | pages = 061001 | year = 2013 | pmid = 23848618 | bibcode = 2013PhRvE..87f1001L | hdl = 1969.1/185287 | hdl-access = free }} and experiments in a vacuum chamber{{Cite journal | last1 = King | first1 = J. | last2 = Lind | first2 = S. | title = The Kaye effect: New experiments and a mechanistic explanation | doi = 10.1016/j.jnnfm.2019.104165 | journal = Journal of Non-Newtonian Fluid Mechanics | volume = 273 | pages = 104165 | year = 2019 | doi-access = free }} that an extremely thin layer of air (approximately 1000 times thinner than the jet diameter) is entrained, which acts as a lubricant and supports the sliding jet.

The current theory is that viscoelasticity is key. In a jet viscoelastic fluid, a portion of the energy of deformation as the jet falls is recoverable, and this reduces the force required to support the leaping jet, enabling more air to be entrained.