Conventional wisdom has held that all fluids containing polymers should form the beads, but researchers have shown that assumption to be wrong and have demonstrated why.
The researchers tested saliva and a material contained in a strip on the leading edge of disposable razors.
"You moisten the razor strip with water, which causes it to swell, press it against a finger and pull it," Basaran said. "Unlike saliva, you see strands of liquids formed but no beads."
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 are 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.
"It turns out that the inertia has to be large enough and the relaxation time has to be small enough to form beads," Bhat said.
The researchers discovered bead formation depends on two ratios: the viscous force compared to inertial force and the relaxation time compared to the capillary time.
Because smearing "satellite" beads form around droplets produced by an inkjet printer, learning how to control bead formation might be used to improve printing. Findings also may help to improve an industrial process called electrospinning, used to make a variety of products, and spray coating used in painting.
"The idea is that, if you are operating an inkjet printer, for example, you would be able to control these ratios to prevent the bead formation," Basaran said.
Findings may help to perfect a new type of drug-dispensing technology being developed for "per
|Contact: Emil Venere|