Analysis of direct force measurements during capillary pinching of visco-elastic fluids in CaBER type experiments

Abstract

A novel device is presented for direct measurement of the axial force evolution during the pinching of fluid filaments following an extensional step stretch, based on the “tilted-CaBER.” The bending curve of a horizontally orientation fluid filament is fitted with the full expression of a catenary function, to directly and unambiguously extract the axial force from a single fitting parameter. The general limits of axial force determination from such devices are introduced in terms of a Bond number that accounts for the axial length scale. The new set-up is validated using a Newtonian PDMS oil, for which the axial force scaling and the related prefactors X of the similarity solution are known. For dilute polymer solutions in form of a Boger fluid, the so far theoretical factor X = 1.5 for an Oldroyd-B model fluid could be experimentally approached for the first time with the new setup.