Atomization and elongational viscosity of associating triblock copolymer solutions

Elongational viscosity and drop size distribution upon atomization are measured 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 thickening of shear viscosity. Measurements conducted in an opposing jet elongational rheometer indicate that the elongational viscosity also exhibits associative thickening. However, the ratio of elongational viscosity to shear viscosity 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 viscosity similar to a series of Newtonian oils of comparable surface tension. (C) 2001 Elsevier Science B.V. All rights reserved.