17-Feb-2012

Scientists solve whether a liquid thread will break up into drops

Scientists at Cambridge University in the UK have developed a method for predicting whether a filament of fluid will condense along its length into a single droplet, or collapse into multiple droplets.

The research, published today (17 February) in the journal Physical Review Letters, could help in designing processes for the dispersion of drugs for inhalation, or for paint spraying or inkjet printing.

Author Dr Alfonso Arturo Castrejon Pita, said: ‘For the first time in an experimental and quantitative way, the ultimate behaviour of a filament under nothing but the action of viscous and surface tension forces has been explored.’

The University of Cambridge team, led by Professor Ian Hutchings, developed a large-scale, fully controlled model of a printhead to recreate the process of droplet generation. Using a simple fluid solution, consisting of water and glycerine, the team gradually increased the viscosity of the working fluid by increasing the amount of glycerine in the mixture. The entire process of droplet generation was then recorded using ultrafast imaging techniques to observe how long threads, or filaments (rather than drops), were being generated, which, when sufficiently viscous, would be several centimetres long and one tenth of a millimetre thick. Furthermore, these long filaments would not break up but instead slowly contract to form a single drop.

Professor Hutchings said: ‘Our regime diagram can predict whether or not a certain liquid can be broken into useful droplets; it is, in simple words, a rule of thumb to determine whether a liquid can be used to produce a droplet or not.’

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