Deformation and necking of liquid droplets in a magnetic field

Abstract

Pendant droplets of water and paramagnetic solutions are studied in the presence of uniform and nonuniform magnetic fields produced by small permanent magnet arrays, both in static conditions and during dynamic pinch-off. Static measurements of the droplet shape are analysed in terms of an apparent surface tension γapp or an effective density ρeff. The change of surface tension of deionized water in a uniform field of 450 mT is insignificant, 0.19 {plus minus} 0.21 mNm-1. Measurements on droplets of compensated zero-susceptibility solutions of Cu2+, Mn2+ and Dy3+ where the shape is unaffected by any magnetic body force show changes of surface tension of about -1% in 500 mT. Magnetic field gradients of up to 100 T2m-1 deform the droplets and lead to changes of ρeff that are negative for diamagnetic solutions (buoyancy effect) and positive for paramagnetic solutions. The droplet profile of strongly-paramagnetic 0.1 Dy M DyCl3 solution is analysed, treating the nonuniform vertical field gradient as a spatial variation of gravity. The influence of Maxwell stress on droplet shape is discussed. In dynamic measurements, the droplet shape at pinch-off is recorded by high-speed photography and analysed in terms of a relative change of dynamic surface tension in the presence of a magnetic field. The surface-tension-dependent pre-factor of the scaling law that governs the pinch-off dynamics shows no difference for pure water or 0.11 M DyCl3 solutions in the field. The nonuniform field has no influence in the pinch-off region because the filament diameter is much less than the capillary length.

A Machine Learning Approach to Predict Fluid Viscosity Based on Droplet Dynamics Features

“…Broboana et al [29] referred to this as the transitory regime (TR). In the article by Castrejón-Pita et al [16], experimental data at Oh = 1.81 also show a contraction process with an exponent greater than 1 following the inertia region (regime I), a phenomenon commonly observed in other experimental studies [21,23,27,28,30]. However, there is currently no comprehensive theoretical explanation for this contraction process.…”

“…Jiang et al judged the contraction regime based on the exponential size of the contraction curve, with an exponent of 2/3 being the inertial regime (I), and an exponent of 1 being the viscous regime (V) as well as the viscousinertial regime (IV). Similar to the way other researchers judge changes in contraction regions [23,[28][29][30][31], their judgments of V and IV tenses are based on two non-overlapping, exponentially 1 contractions.…”

“…The results of this study showed that the neck contraction and fracture process of droplets bouncing and separating after the collision is consistent with the scalar law of the drop as it falls. Poulose et al [23] investigated the neck shrinkage kinetics of paramagnetic solutions in a magnetic field environment. Wang et al [24] and Rubio et al [25] investigated the droplet dropping and liquid bridge stretching in an electric field environment, respectively.…”

Alveolar type II epithelial cell FASN maintains lipid homeostasis in experimental COPD

“…The surface and interfacial activity of the mouse pulmonary surfactants was determined using the commercial DataPhysics OCA 25 instrument, as described previously ( 80 ). Briefly, 27 μL of murine BALF was dispensed into a droplet from the nozzle.…”

“…The density (kg/m 3 ) of the liquid was measured and inputted and the surface tension of the droplet measured in zero field γ0. The surface tension (IFT mN/m) was then calculated by determining the shape of the droplet, with a change in droplet shape equating to a change in surface tension ( 80 ). Each measurement was repeated for a minimum of 4 droplets.…”