STABILITY OF VISCOELASTIC DYNAMIC CONTACT LINES - AN EXPERIMENTAL-STUDY

An experimental study of the rivulet instability associated with spin coating a circular drop of fluid is conducted to examine the effect of elasticity on the onset and evolution of the instability. The spin co ating experiments are conducted with viscoelastic drops consisting of a high molecular weight polystyrene in tricresyl phosphate (TCP), as w ell as the Newtonian solvent TCP. Results show an unequivocal delay in the onset of the instability when the appropriate Weissenberg number is sufficiently large, resulting in a larger coated area and more fing er arms relative to Newtonian results. Experiments performed with the viscoelastic fluid at low Weissenberg number exhibit similar behavior to those performed with the Newtonian solvent as expected. Additionall y, the growth rate of the instability is reduced for experiments in wh ich the elastic forces are important, in agreement with the perturbati on theory of Spaid and Homsy [Phys. Fluids 8, 460 (1996)], demonstrati ng that elastic forces have a stabilizing influence on the contact lin e instability. (C) 1997 American Institute of Physics.