arXiv subjects

Masoodah Gunny

Publications and source records attributed to Masoodah Gunny.

3 recordsLinked to original sources

arXiv2026

Taylor dispersion in a soft tube

Diffusion of a solute along a tube is enhanced by hydrodynamic flow, a phenomenon known as Taylor dispersion. In microfluidic applications, the compliance of the tube boundaries modifies the hydrodynamic flow and thus solutal transport. Here, we develop the theory of solutal dispersion in a soft, axisymmetric tube where the tube walls respond to the hydrodynamic pressure through a Winkler response. By deriving the modified macro-transport equation for the solutal concentration dynamics based on multiple-time-scale analysis, we explore the influence of softness on solutal transport for steady and pulsatile configurations. Our main finding is that softness enhances the effective advection velocity and dispersion coefficient, which might have practical implication in biology and microfluidic technology.

cond-mat.soft↗

arXiv2026

Near-surface colloidal dynamics in jammed and slipping microgel suspensions

Jammed suspensions of soft microgel particles may exhibit slippage along smooth boundaries. Owing to their expected sub-micrometric dimensions, direct observations of dynamics within the near-surface layers supposed to be responsible for this slippage have been difficult to achieve. Here, we use total internal reflection fluorescence microscopy (TIRFM) to observe nanoparticle dynamics near glass/microgel-suspension interfaces. Indicating near-wall dynamic heterogeneity, velocity profiles for suspensions are nonlinear. These profiles tend to a constant slippage velocity at submicrometric distances from the wall, consistent with macroscopic wall slip measurements. Furthermore, nanoscale particle altitude distributions are strongly dependent on the slip velocity, revealing a dynamically-mediated and nanoscale particle-organisation effect. The collected observations give support for the existence of near-wall heterogeneity as a dominant mechanism contributing to microgel wall slip. Our work also opens new perspectives for the study of particle dynamics and organisation in complex interfacial environments.

cond-mat.soft↗

arXiv2025

Droplet-on-demand using a positive pressure pulse

Droplet generation under steady conditions is a common microfluidic method for producing biphasic systems. However, this process works only over a limited range of imposed pressure: beyond a critical value, a stable liquid jet can instead form. Furthermore, for a given geometry the pressure conditions set both the generation rate of droplets and their volume. Here, we report on-demand droplet production using a positive pressure pulse to the dispersed-phase inlet of a flow-focusing geometry. This strategy enables confined droplet generation within and beyond the pressure range observed under steady conditions, and decouples volume and production rate. In particular, elongated plugs not possible under steady conditions may be formed when the maximal pressure during the pulse reaches the jet regime. The measured volume of droplets-on-demand, as well as the onset of droplet generation are both captured with a simple model that considers hydraulic resistances. This work provides a strategy and design rules for processes that require individual droplets or elongated plugs in a simple microfluidic chip design.

physics.flu-dyn↗