Direct measurements of slip in sheared polymer solutions

Abstract

We report direct measurements of slip flow during and after plane-Couette shearing of poly(styrene) solutions between glass surfaces. Slip is studied by visualizing the microscopic motions of micron-sized silica spheres suspended in the solutions. Slip velocities as large as 4 μm s−1 are observed during shear, and recoil displacements of as much as 80 μm are observed at the glass surfaces after the driving surface stops moving. Significant slip is observed when the Weissenberg number $\lambda\dot{\gamma}$ exceeds 0.5 or so, where λ is the relaxation time and $\dot{\gamma}$ the shear rate. The magnitude of the slip correlates strongly with the fluid's birefringence, indicating that slip is induced by polymer stress or orientation. Away from the centre of the sample, toward the free edges, a secondary flow is observed, which appears to be driven by a normal-stress imbalance at these edges.

Flow pattern and molecular visualization of DNA solutions through a 4:1 planar micro-contraction

“…Wall slip phenomena of entangled solutions [27][28][29] and melts [30][31][32][33][34] have been studied for a long time in both capillary and shear flow. The slip due to lack of entanglement at the interface can be quantitatively described according to the following formula for the Navier-de Gennes extrapolation length b [34,35] …”

Numerical simulation of bubble growth in Newtonian and viscoelastic filaments undergoing stretching

“…The role of surface energy and interfacial friction was also studied [31]. Measurements of slip flow of polystyrene solutions have also been performed by Archer et al [32] through visualization of the microscopic motions of silica spheres suspended in solution in a plane Couette flow. At high enough stress values (high Weissenberg numbers), slip was so strong that the slip length could exceed by several orders of magnitude the particle molecular size [33,34].…”

“…Eq. (32) suggests that: the maximum value of T 1 is obtained for r = 0 and z = 0 or z = H, that of T 2 for r = 0 and z = H/2, and that of T 3 for r = 0 and z = 0 or H. For these values of r and z, one can further confirm that the maximum tension criterion is determined by the sign of T 2 while the sign of T 1 (or that of T 3 ) determines the minimum tension criterion. Simple algebraic calculations then result in the following expression/value of the critical capillary number for which the minimum tension criterion is satisfied: Ca c ≡ (ηU 0 /σ) c = P atm H/3σ ≈ 10 5 (200 ×…”

A Coherent Description of Nonlinear Flow Behavior of Entangled Polymers as Related to Processing and Numerical Simulations

“…The planar Couette shear generated in a sliding plate device could suffer flow instabilities including interfacial failure [36] and secondary flow, [39] which are inevitable for well entangled melts, thanks to the large meniscus. Meniscus can be minimized, essentially leading to elimination of instabilities, by employment of a co-cylinder shear cell where an inner cylinder is displaced against a fixed outer cylinder.…”