Determination of viscosity from drop deformation

A novel technique for measuring viscosities of droplets is described. This technique uses the transient and steady state deformation of a droplet susp ended in an immiscible fluid. Drop viscosities are derived from small defor mation theory as eta (d) = (-5 gamma /2(s)alpha -1.5)eta (s), for hyperboli c flow. and eta (d) = (-5 gamma /4D(s)alpha- 1.5)eta (s) for shear flow. He re y is the flow rate, D-s is the steady state deformation, alpha is the ex ponent obtained from deformation growth or relaxation, and eta (s), is the suspending fluid viscosity. Drop viscosities measured using this technique, implemented on a four-roll mill apparatus, are compared with bulk viscosit ies measured using a conventional rheometer. The measurement scope of the n ew technique, with respect to capillary number, drop size, and viscosity ra tio, is defined. (C) 2001 The Society of Rheology.