Shear flow in a two-dimensional Couette cell: A technique for measuring the viscosity of free-standing liquid films

A two-dimensional shear viscometer has been constructed and tested using free-standing liquid soap films. The viscometer, which is an analog of a three-dimensional Couette cell, consists of an inner rotating disk and an outer stationary ring. The viscosity of the liquid films can be reliably obtained by measuring either the transient response of the disk upon a stepwise increment of the applied stress on the disk, or by measuring the strain-stress relation in the steady state. The design can be easily modified to accommodate other types of flow which are useful for investigating hydrodynamic and theological behavior in a variety of thin films, such as liquid crystal and polymer films. (C) 1995 American Institute of Physics.