Journal of Non-Newtonian Fluid Mechanics, 30 (1988) 285-302 zyxwvutsrqponmlkjihgfedcbaZ Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands zyxwvutsrqponmlkjihgf 285 zyxwvuts FLUID DETACHMENT AND SLIP IN EXTENSIONAL FLOWS T. SRIDHAR Department of Chemical Engineering, Monash University, Clayton, Victoria, 3168 (Australia) and R.K. GUPTA Department of Chemical Engineering, State University of New York at Buffalo, Amherst, N.Y. 14260 (U.S.A.) (Received November 27, 1987; in revised form March 5, 1988) Summary 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. 1. Introduction The interactions of a polymeric material with a solid surface are increas- ingly being recognized as an area requiring attention. Such a study may hold the key to a better understanding of instabilities in polymer processing operations and it is also important in such diverse areas as adhesion. Conventional fluid mechanics postulates a no-slip boundary condition at a solid surface, but for polymer melts and solutions such a constraint does not 0377-0257/88/%03.50 0 1988 Elsevier Science Publishers B.V.