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 the 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.

Temperature-controlled dripping-onto-substrate (DoS) extensional rheometry of polymer micelle solutions

“…However, a temperature control chamber has yet to be incorporated into DoS rheometry, whereas heated CaBER has been developed both commercially and via custom design. 22,29,30 In commercial CaBER instruments, the two end plates are heated and cooled by circulating fluid, and the measurement cell is enclosed within a double cover. Consequently, commercial CaBER instruments can be used to measure solution extensional rheology at temperatures between 0 and 60 1C, albeit with limited temperature accuracy given that only the plates are heated.…”

“…To measure the extensional rheology of motor oils, Du et al 22 constructed a customized CaBER in which the two endplates were enclosed in an acrylic chamber and heated using resistance heating modules that can maintain a temperature up to 250 1C. Most recently, Van Aeken et al 30 constructed a CaBER-based instrument with a brass fluid bath to enable horizontal extensional measurements in an external fluid; to conduct measurements at elevated temperatures, the brass frame can be heated via cartridge heaters. In contrast, in DoS instrumentation introduced by Dinic et al 16 and used by many others, [31][32][33][34] the sample is exposed to the environment and lacks heating elements.…”

“…The chamber employs heaters for the nozzle, substrate, and enclosure to heat both the sample and the environment, distinguishing our instrument from commercial and custom CaBER chambers that only heat the endplates 22 or only heat the sample environment. 30,46 We characterize the temperature-dependent extensional behavior of a model system consisting of 4 wt% poly(ethylene oxide)-bpoly(propylene oxide)-b-poly(ethylene oxide) (poloxamer 234, i.e. P234) in 0.9 M NaF, which forms spherical micelles at room temperature that lengthen into WLMs at elevated temperatures.…”