Capillary Break-up Rheometry of Low-Viscosity Elastic Fluids

Abstract

We investigate the dynamics of the capillary thinning and break-up process for low viscosity elastic fluids such as dilute polymer solutions. Standard measurements of the evolution of the midpoint diameter of the necking fluid filament are augmented by high speed digital video images of the break up dynamics. We show that the successful operation of a capillary thinning device is governed by three important time scales (which characterize the relative importance of inertial, viscous and elastic processes), and also by two important length scales (which specify the initial sample size and the total stretch imposed on the sample). By optimizing the ranges of these geometric parameters, we are able to measure characteristic time scales for tensile stress growth as small as 1 millisecond for a number of model dilute and semi-dilute solutions of polyethylene oxide (PEO) in water and glycerol. If the final aspect ratio of the sample is too small, or the total axial stretch is too great, measurements are limited, respectively, by inertial oscillations of the liquid bridge or by the development of the well-known beads-on-a-string morphology which disrupt the formation of a uniform necking filament. By considering the magnitudes of the natural time scales associated with viscous flow, elastic stress growth and inertial oscillations it is possible to construct an “operability diagram” characterizing successful operation of a capillary breakup extensional rheometer. For Newtonian fluids, viscosities greater than approximately 70 mPas are required; however for dilute solutions of high molecular weight polymer, the minimum viscosity is substantially lower due to the additional elastic stresses arising from molecular extension. For PEO of molecular weight 2 · 106 g/mol, it is possible to measure relaxation times of order 1 ms in dilute polymer solutions with zero-shear-rate viscosities on the order of 2 – 10 mPas.

Shear and extensional properties of kefiran

“…The values of Bo estimated according equation (3) are around 1.47-1.60, being consistent with the typically established condition √ , maintained in order to keep the initial configuration close to cylindrical (Rodd et al, 2005).…”

Flow patterns in 4:1 micro-contraction flows of viscoelastic fluids

“…The relaxation times were measured using capillary breakup extensional rheometry (CaBER), which is appropriate for the measurement of low viscosity polymer solutions (Rodd et al, 2005). The range of relaxation times for the solutions measured by CaBER were 44 < λ < 82 ms (Rodd et al, 2004). The steady shear viscosity was measured using a strain controlled rheometer (ARES) and, the zero-shear viscosity was in the range of 0.17 Flow patterns in 4:1 micro-contraction flows of viscoelastic fluids < η 0 < 39 Pa·s.…”

Analysis on the ink transfer mechanism in R2R application

“…However, due to the lack of proper investigation methods of free surface, most of the earlier works were inaccurate. In several investigations, the presence of free surface was handled with the so-called filament stretching method, but omission of the effect of convection and rotation made their analyses less physically realistic [6][7][8][9].…”