Polymer-polymer interfacial slip by direct visualization and by stress reduction

We studied polymer-polymer interfacial slip in bilayer films of highly immiscible (interaction parameter, χ ≅ 0.1 ) polyethylene and fluoropolymer from medium to higher shear stresses (10–200 kPa) using both visualization and stress reduction. We found good agreement between results from the two methods as well as with previous studies using multilayers by Lee et al. [J. Rheol. 53, 893–915 (2009)] and visualization of flow in a transparent capillary by Migler et al. [J. Rheol. 45, 565–581 (2001)]. We observed two power-law regions: V slip ∝ τ 6.2 with a transition to V slip ∝ τ 1.8 at 50 kPa. This is in contrast to the theory of Brochard-Wyart and de Gennes [C. R. Acad. Sci., Ser. II: Mec., Phys., Chim., Sci. Terre Univers 317, 13–17 (1993)], which predicts a transition from infinite slope to a slope of one at a critical stress.