We investigated pressure-driven transport of an immiscible binary system, constituted by two electrically conducting liquids, in a narrow fluidic channel under the influence of an externally applied magnetic field. The surface wettability was taken into account in the analysis considering that the walls of the channel are chemically treated to obtain various predefined contact angles as required for the study. Alterations in the capillary filling and wetting dynamics in the channel stemming from a complex interplay among different forces acting over the interface were investigated. It was shown that an alteration in the strength of the magnetic field leads to an alteration in the dynamics of the interface, which in turn, alters the filling and wetting dynamics nontrivially upon interaction with the surface tension force due to the wetted walls of the channel. It is emphasized that a contrast in properties of constituents of the binary system gives rise to an alteration in the forces being applied across the interface, leading to an intricate control over the filling and wetting dynamics for a given flow configuration and an applied field strength. We believe that the results obtained from this analysis may aid the design of microfluidic devices used for multiphase transport.

We numerically investigate the dynamics of two immiscible conductive fluids in a narrow fluidic channel under the combined influence of electric and magnetic fields using a diffuse interface based phase-field model. The numerical solver is validated from two different perspectives, viz., with the reported results of microscale multiphase transport as well as the available experimental results in the paradigm of electrically actuated transport. The magnetic field induces the Lorentz force due to its interaction with the electrical forcing, which in turn leads to complex interfacial dynamics and development of a finger-like interface front of the advancing fluid into the receding fluid. Under certain conditions studied in the present work, the trend reverses, and a finger of receding fluid is formed into the advancing fluid. The effect of contrast in fluid properties is studied and the interface breaking phenomenon is observed beyond a threshold viscosity contrast. It is found that for a given viscosity contrast between the fluids, an increase in the strength of the applied magnetic field prevents wetting failure.

The filling characteristics of a Newtonian electrolyte through a microchannel with grafted polyelectrolyte layer on its inner walls have been investigated. A reduced order model has been deployed for the analysis. The streaming potential triggered by the interfacial electrochemistry, followed by an involved electrostatic interaction between polyelectrolyte macromolecules and the electrolytic ions, alters the filling characteristics in the microchannel. An oscillatory behavior of the filling dynamics is observed as the interface moves in the capillary. It has been demonstrated that the capillary filling dynamics can be altered through selective and tunable input parameters used in the investigation. A qualitative study has been performed on the variation in the filling dynamics by invoking scaling-estimates of the reduced order model. The scales of various participating forces on a spatiotemporal map have been identified to demarcate various regimes of the filling dynamics.

We have presented an experimental analysis on the investigations of capillary filling dynamics of inelastic non-Newtonian fluids in the regime of surface tension dominated flows. We use the Ostwald–de Waele power-law model to describe the rheology of the non-Newtonian fluids. Our analysis primarily focuses on the experimental observations and revisits the theoretical understanding of the capillary dynamics from the perspective of filling kinematics at the interfacial scale. Notably, theoretical predictions of the filling length into the capillary largely endorse our experimental results. We study the effects of the shear-thinning nature of the fluid on the underlying filling phenomenon in the capillary-driven regime through a quantitative analysis. We further show that the dynamics of contact line motion in this regime plays an essential role in advancing the fluid front in the capillary. Our experimental results on the filling in a horizontal capillary re-establish the applicability of the Washburn analysis in predicting the filling characteristics of non-Newtonian fluids in a vertical capillary during early stage of filling (Digilov 2008 Langmuir 24 , 13 663–13 667 ( doi:10.1021/la801807j )). Finally, through a scaling analysis, we suggest that the late stage of filling by the shear-thinning fluids closely follows the variation x ~ t . Such a regime can be called the modified Washburn regime (Washburn 1921 Phys. Rev. 17 , 273–283 ( doi:10.1103/PhysRev.17.273 )).