Atomization and elongational viscosity of associating triblock copolymer solutions

Elongational viscosity and drop size distribution upon atomization are meas ured for a series of Kraton (styrene-butadiene-styrene triblock copolymer) solutions prepared with blended solvents of toluene and heptane. At a blend ratio of 25% toluene/75% heptane, the solvent quality becomes poor for the styrene blocks, resulting in micro phase separation and associative thicke ning of shear viscosity. Measurements conducted in an opposing jet elongati onal rheometer indicate that the elongational viscosity also exhibits assoc iative thickening. However, the ratio of elongational viscosity to shear vi scosity remains near the Newtonian value of three, indicating little or no enhancement of elongational viscosity due to viscoelasticity. Droplet size distributions for all Kraton solutions, including the solutions exhibiting associative thickening, follow a relationship between drop size and shear v iscosity similar to a series of Newtonian oils of comparable surface tensio n. (C) 2001 Elsevier Science B.V. All rights reserved.