Motility and pairwise interactions of chemically active droplets in one-dimensional confinement.

Self-propelled droplets serve as ideal model systems to delve deeper into understanding the motion of biological microswimmers by simulating their motility. Biological microorganisms are renowned for showcasing a diverse array of dynamic swimming behaviors when confronted with physical constraints. This study aims to elucidate the impact of physical constraints on swimming characteristics of biological microorganisms.

Pattern Formation in Evaporating Polymer Solutions-Interplay between Dewetting and Decomposition.

Pattern formation during solution evaporation is common in several industrial settings and involves a complex interplay of multiple processes, including wetting/dewetting, diffusion, and rheological characteristics of the solution. Monitoring the emergence of patterns during evaporation under controlled conditions may allow deconvolution of different processes and, in turn, improve our understanding of this common yet complex phenomenon. Here, we probe the importance of initial conditions, defined by the solution concentration , on the pattern formation in evaporating polymer solutions on the air-water interface.

Harnessing Polar Interactions Tunes the Stability of Ultrathin Polymer Solution Films.

The stability of ultrathin (<100 nm) polymer films is essential in applications like protective coatings. On the contrary, their instability may actually be desirable for the emergence of self-assembled nanoscale patterns utilized in the fabrication of functional devices. Polymer solution films exhibit two distinct kinds of instabilities, viz.

Nature of instability in flow-driven porous anodic oxide.

Self-organized porous anodic oxide films are formed by the electrochemical oxidation of reactive metal aluminum in acidic solutions in which the oxide is soluble. Recently, viscous flow models have shown using linear stability analysis that the instability results from a trade-off between the destabilizing effect of viscous flow of oxide and the stabilizing effect of oxide formation, which provides the wavelength selection mechanism for pattern formation. Anion adsorption on surface growth sites causes nonuniform compressive stress at the oxide-solution interface, which drives the flow.

Universal scaling law for electrified sessile droplets on a lyophilic surface.

Electrified sessile droplets on solid surfaces are ubiquitous in nature as well as in several practical applications. Although the influence of electric field on pinned sessile droplets and soap bubbles has been investigated experimentally, the theoretical understanding of the stability limit of generic droplets remains largely elusive. By conducting a theoretical analysis in the framework of lubrication approximation, we show that the stability limit of a sessile droplet on a lyophilic substrate in the presence of an electric field exhibits a universal power-law scaling behavior.

Reduced-Order Model for Surfactant-Laden Electrified Sessile Droplets.

A comprehensive understanding of the physics of electrowetting of a surfactant-laden droplet is important for applications in rapid healthcare diagnostics. A majority of biological samples examined during point-of-care (POC) diagnostics are biofluids with dissolved surfactants, such as the respiratory droplets containing protein (mucin) and surfactant molecules like dipalmitoylphosphatidylcholine. The presence of these surfactant molecules is anticipated to have a significant impact on the performance of electrowetting-based POC diagnostic devices.

Electrokinetic Thin-Film Model for Electrowetting: The Role of Bulk Charges.

The electrowetting behavior of a charge-carrying sessile droplet is relevant to applications such as point-of-care diagnostics. Often biomedical assays involve droplets that contain charged molecules such as dissolved ions, proteins, and DNA. In this work, we develop a reduced-order electrokinetic model for electrowetting of such a charge-carrying droplet under a parallel-plate electrode configuration.

Mode switching of active droplets in macromolecular solutions.

Typical bodily and environmental fluids encountered by biological swimmers consist of dissolved macromolecules such as proteins or polymers, rendering them even non-Newtonian at times. Active droplets mimic the essential propulsive characteristics of several biological swimmers, and serve as ideal model systems to widen our understanding of their locomotive strategies. Here, we investigate the motion of a micellar solubilization driven active oil droplet in an aqueous medium consisting of polymers as macromolecular solutes.

Deforming active droplets in viscoelastic solutions.

The motion of biological swimmers in typical bodily fluids is modelled using a system of micellar solubilization driven active droplets in a viscoelastic polymeric solution. The viscoelastic nature of the medium, as perceived by the moving droplet, characterized by the Deborah number (De), is tuned by varying the surfactant (fuel) and polymer concentration in the ambient medium. At moderate De, the droplet exhibits a steady deformed shape, markedly different from the spherical shape observed in Newtonian media.

Equivalence of sessile droplet dynamics under periodic and steady electric fields.

The electrohydrodynamics of a sessile droplet under the influence of periodic and steady electric fields in microgravity conditions is theoretically investigated using an inertial lubrication model. Previous studies have revealed that a freely suspended spherical droplet with unequal conductivity and permittivity ratios exhibits distinct dynamics under periodic and equivalent steady forcing in the root mean-square sense. However, it is unclear when (if at all) such distinct dynamics occur for periodic and equivalent steady forcing in the case of sessile droplets.