Researchers study polymer beading

June 16, 2010 at 1:19 PM
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HOUSTON, June 16 (UPI) -- U.S. scientists say they've solved a basic scientific question about why some fluids containing polymers form beads when they are stretched and others do not.

Researchers led by Rice University Professor Matteo Pasquali, Purdue University Professors Osman Basaran and Michael Harris and Massachusetts Institute of Technology Professor Gareth McKinley said their findings could lead to improvements in such fields as in ink-jet printing, nanomaterial fiber spinning and drug dispensing for personalized medicine.

The researchers said they discovered a key factor in the beading mechanism is fluid inertia, or the tendency of a fluid to keep moving unless acted upon by an external force. Other major elements include a fluid's viscosity -- the time it takes a stretched polymer molecule to "relax," or snap back to its original shape when stretching is stopped -- and the "capillary time," or how long it would take for the surface of the fluid strand to vibrate if plucked.

The scientists said they discovered bead formation depends on two ratios: the viscous force compared with inertial force and the relaxation time compared with the capillary time.

The study that included Purdue graduate student Santosh Appathurai and former Rice postdoctoral researcher Pradeep Bhat appears in the online early edition of the journal Nature Physics.

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