Why saliva forms beads when stretched?

Washington (IANS)- Some fluids, including saliva, form beads when they are stretched as they contain polymers which cause a line of beads to form just before the strand breaks.

Study co-author Matteo Pasquali, Rice University professor in chemical and biomolecular engineering, said the study could lead to improvements as diverse as ink-jet printing, nanomaterial fiber spinning and drug dispensers for "personalised medicine".

Co-author Osman Basaran, Purdue University professor of chemical engineering, said: "Any kindergartner is familiar with this beading phenomenon, which you can demonstrate by stretching a glob of saliva between your thumb and forefinger."

"The question is: 'Why does this beading takes place only in some fluids containing polymers but not others'?" he asked.

Pasquali said: "In answering this question, we are addressing everyday processes that apply to fibre and droplet formation, not just in multibillion-dollar industrial plants but also in fluids produced in living cells."

Saliva and other complex "visco-elastic" fluids like shaving cream and shampoo contain long molecules called polymers.

When a strand of viscoelastic fluid is stretched, these polymers can cause a line of beads to form just before the strand breaks.

The origins of the work can be traced to Pasquali's and Basaran's doctoral research adviser, L.E. "Skip" Scriven of the University of Minnesota, said a Rice and Purdue release.

The findings are published online this week in Nature Physics.