Wall Slip of Narrow Molecular Weight Distribution Polybutadienes

A series of polybutadienes $\text{(78,000⩽}{\mathrm{M}}_W\text{⩽240,000),}$ each with a narrow molecular weight distribution (M_W/M_N<1.1), was extruded through slit capillary dies. Signals from a pressure traducer and from hot‐film anemometers embedded in the capillary wall were used to infer the behavior of the polymer at the wall. Although slip flow was not observed for polymers with ${\mathrm{M}}_{\mathrm{W}}\text{=78,000}$ over the range of flow rates available, the higher molecular weight species showed a pattern of no‐slip, alternate sticking and slipping, and slip flow as the flow rate was increased. Slip velocities were estimated using a three‐dimensional model of heat transfer from the hot‐film probe. In the stick‐slip regime, there is a distinct asymmetry between the process of breakdown of continuity at (or very near) the wall, and the re‐establishment of a no‐slip boundary condition.