We study both numerically and experimentally the breakup of a viscoelastic liquid bridge between two parallel electrodes. We solve the leaky-dielectric FENE-P model to describe the dynamical response of the liquid bridge under isothermal conditions. The results show that the surface charge screens the inner electric field perpendicular to the free surface over the entire dynamical process. The liquid bridge deformation produces a normal electric field on the outer side of the free surface that is commensurate with the axial one. The surface conduction does not significantly affect the current intensity in the time interval analyzed in the experiments. The force due to the shear electric stress becomes comparable to both the viscoelastic and surface tension forces in the last stage of the filament. However, it does not alter the elasto-capillary balance in the filament. The extensional relaxation times approximately coincides with the stress relaxation time prescribed in the FENE-P model. We measure experimentally the filament electrical conductivity and extensional relaxation time for PEO dissolved in deionized water and in a mixture of water and glycerine. We compare the filament electrical conductivity with the value measured in hydrostatic conditions for the same estimated temperature. Good agreement was found for PEO dissolved in water+glycerine, which indicates that the change of the filament microscopic structure due to the presence of stretched polymeric chains does not significantly alter the ion mobility in the stretching direction. Significant deviations are found for PEO dissolved in deionized water that may be attributed to the heat transferred to the ambient, neglected in the calculation of the filament temperature. The extensional relaxation time measured from the images acquired during the filament thinning hardly depends on the applied voltage.
We investigate the effects of dissipative air drag on the dynamics of electrified jets in the initial stage of the electrospinning process. The main idea is to use a Brownian noise to model air drag effects on the uniaxial elongation of the jets. The developed numerical model is used to probe the dynamics of electrified polymer jets at different conditions of air drag force, showing that the dynamics of the charged jet is strongly biased by the presence of air drag forces. This study provides prospective beneficial implications for improving forthcoming electrospinning experiments.
We study experimentally and numerically the thinning of a Newtonian leaky-dielectric filament subject to an axial electric field. We consider moderately viscous liquids with high permittivity. The experiments show that satellite droplets are produced from the breakup of the filaments with high electrical permittivity due to the action of the electric field. Two electrified filaments with the same minimum radius thin at the same speed regardless of when the voltage was applied. The numerical simulations show that the polarization stress is responsible for the pinching delay observed in the expe…
We studied experimentally the breakup of liquid bridges made of aqueous solutions of Poly(acrylic acid) between two separating solid surfaces with freely moving contact lines. For polymer concentrations higher than a certain threshold ($\sim$ 30 ppm), the contact line on the surface with the highest receding contact angle fully retracts before the liquid bridge capillary breakup takes place at its neck. This means that all the liquid remains attached to the opposing surface when the surfaces are separated. This behavior occurs regardless of the range of liquid volume and stretching speed studi…
In this paper, we experimentally explore the formation, evolution and breakup of Armstrong liquid bridge. The extremely complicated evolution stage is revealed, which involves many coupled processes including the morphology change, current variation, heat transfer, and water evaporation. By focusing on the final fate of this liquid bridge, we observe that the breakup occurs once an effective length ($\tilde{L}$) is reached. This effective length increases linearly with the applied voltage, implying a threshold electric field to sustain the liquid bridge. Moreover, by an introduced external flo…
How Surface Viscoelasticity Eliminates Satellite Drops
School of Astronautics, Beihang University（北京航空航天大学宇航学院）；Aircraft and Propulsion Laboratory, Ningbo Institute of Technology, Beihang University（北京航空航天大学宁波研究院飞机与推进实验室）
Dripping-onto-droplet rheometry of sodium alginate solutions
Mines Paris, PSL University（巴黎矿业学院，巴黎文理研究大学）；Universidade Estadual Paulista ‘Julio de Mesquita Filho’（圣保罗州立大学）；Universidade Federal do Rio de Janeiro（里约热内卢联邦大学）
A number of commercial fluids, including synthetic automotive oils, food and consumer products containing polymer additives exhibit weakly rate-thickening responses in the final stages of capillarity-driven thinning, where a large accumulated strain and high extensional strain rate alter the thinning dynamics of the slender liquid filament. Consequently, the capillarity-driven thinning dynamics typically feature two distinct regions at the early and late stages of the filament breakup process, each dominated by distinct mechanisms. These features have been incorporated in a simple Inelastic Ra…
