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Highlights • Emphasized the applicability of the newly developed extensional rheometry technique. • Characterized low viscosity commercially used printing inks through extensional rheology. • Performed parametric study on the effect of binder concentration, polymer architecture, molecular weight and solution viscosity. • Characterized inks of relaxation time as low as λ = 160 μ s. • Distinguished jetted inks from non-jettable inks. Abstract In this manuscript, the capillary thinning dynamics of a series of solutions containing polymers commonly used in the coating industry as low-viscosity printing inks were studied. Four different polymer binders were studied in methyl-ethyl ketone. These included one acrylic polymer, one cellulose polymer and two vinyl polymers of different molecular weights. The dripping-onto-substrate capillary breakup extensional rheometry (CaBER-DoS) method was used to characterize the extensional rheology for solutions with viscosities as low as 3.5mPa.s. This technique is based on the measurement of the decay of a fluid filament under the influence of surface tension and has been shown to be capable of measuring relaxation times as low as 20 µs for weakly elastic liquids. The influence of the polymer concentration on the dynamics of filament breakup was investigated for each polymer solution and the results were compared to those obtained with different polymer binders. With an increase in polymer concentration, a critical polymer concentration was identified for the transition between the inertio-capillary, the visco-capillary and the elasto-capillary breakup regimes. With the onset of elasto-capillary breakup at moderate to high polymer concentrations, a delay in the filament breakup was observed due to an increase of the viscous and elastic stresses. This viscoelastic breakup delay would be detrimental to most ink jet printing applications. Within the elasto-capillary breakup regime, the transient extensional viscosity resulted in Trouton ratios ranging from just above the Newtonian limit of Tr = 3 to values close to Tr = 100. [ABSTRACT FROM AUTHOR]

The large extensional viscosity of dilute polymer solutions has been shown to dramatically delay the breakup of jets into drops. For low shear viscosity solutions, the jet breakup is initially governed by a balance of inertial and capillary stresses before transitioning to a balance of viscoelastic and capillary stresses at later times. This transition occurs at a critical time when the radius decay dynamics shift from a 2/3 power law to an exponential decay as the increasing deformation rate imposed on the fluid filament results in large molecular deformations and rapid crossover into the elasto-capillary regime. By experimental fits of the elasto-capillary thinning diameter data, a relaxation time of less than 100 μs has been successfully measured. In this paper, we show that, with a better understanding of the transition from the inertia-capillary to the elasto-capillary breakup regime, relaxation times close to 10 μs can be measured with the relaxation time resolution limited only by the frame rate and spatial resolution of the high speed camera. In this paper, the dynamics of drop formation and pinch-off are presented using dripping onto substrate capillary breakup extensional rheometry (CaBER-DoS) for a series of dilute solutions of polyethylene oxide (PEO) in water and in a viscosified water and glycerin mixture. Four different molecular weights between 100 k and 1 M g/mol were studied with varying solution viscosities between 1 and 22 mPa s and at concentrations between 0.004 and 0.5 times the overlap concentration, c*. The dependence of the relaxation time and extensional viscosity on these varying parameters was studied and compared to the predictions of dilute solution theory while simultaneously searching for the lower limit in solution elasticity that can be detected. For PEO in water, this limit was found to be a fluid with a relaxation time of roughly 20 μs. These results confirm that CaBER-DoS can be a powerful technique characterizing the rheology of a notoriously difficult material to quantify, namely, low viscosity inkjet printer inks. [ABSTRACT FROM AUTHOR]