A new 'twist' to break viscoelastic liquid bridges

(Press-News.org) Scientists have developed a new method that improves dispensing of viscoelastic fluids - a vital process for circuit board production, 3D printing and other industrial applications Viscoelastic fluids are difficult to dispense as liquid bridges that form between the substrate and nozzle must be broken New research has found that twisting these liquid bridges breaks them in a quicker and cleaner way than the conventional method of stretching them Researchers used high speed imaging to observe that when twisted, a crack forms at the edge of the liquid bridge and propagates towards the center The underlying mechanism that breaks the liquid bridge was found to be "edge fracture" and is the first time that scientists have found a useful application for this phenomenon

If you've ever tried to lift a pizza slice covered in hot, melted cheese, you've no doubt encountered the long, cheesy strings that bridge one pizza slice from the next. Keep lifting the pizza slice and these cheese bridges eventually break, covering the plate, table (or even your lap) in long, thin strands of cheese. While this is just a minor inconvenience with pizza, it is a longstanding problem in industry, where liquids with similar properties to melted cheese - dubbed viscoelastic fluids - need to be cleanly and speedily dispensed.

Now, scientists have developed a new technique that uses rotation to break these liquid bridges. Their findings, published 11 June 2021 in PNAS, could improve the speed and precision of dispensing viscoelastic fluids, in applications ranging from circuit board production and food processing to live tissue engineering and 3D printing.

"Viscoelastic fluids, like ketchup, silly putty and toothpaste, have very strange properties - when squeezed slowly, they flow like a fluid, but at faster speeds, they act like an elastic solid," said co-first author, San To Chan, who is a PhD student and JSPS DC2 Fellow in the END