Fluid detachment and slip in extensional flows

It is shown that under certain conditions it is possible to pull a fluid, flowing in a tube, away from the wall. The breakdown of adhesion as a result of the application of extensional deformation is demonstrated and the critical stress is measured. The experiments show that detachment takes place when the apparent extensional viscosity of the liquid near the solid surface reaches a critical value. The critical extensional viscosity depends only on the solution rheology and the material the tube is contructed of. This work shows the necessity of considering both shearing and extensional deformation when analysing slip in polymer processing operations.