flairsLab

Ongoing projects

Surfactant laden film stability, impact, and entrainment.
Molecular models for oils and anti-foams.
Machine learning framework for surfactants.
Moelcular modeling of Phoretic flows for fluid-surfactant systems.

Surfactants, Oils and Anti-foams

Sponsored by Shell Global Solutions, this project aims to solve a number of long-standing issues relevant to lubrication of highly efficient engines.
The presence of Surface active agents, or surfactants alters the surface properties of a liquid, and gives rise to a rich and wide variety of surface events. And the underlying physics becomes rapidly complicated and intertwined. Our most recent investigation aims to understand some of the impacts of surfactants on the stability and evolution of thin liquid films with an aim to bridge the molecular details with continuum scale understanding (ongoing).

Stability and Rupture of Thin Liquid Films

Deterministic hole formation precedes stochastic film rupture - an idea we have demonstrated for thin films, and can be extended to social science and modelling human behaviour!

Thin films, bubbles and membranes are central to numerous natural and engineering processes, i.e., in thin-film solar cells, coatings, biosensors, electro-wetting displays, foams, and emulsions. Yet, the characterization and an adequate understanding of their rupture is limited by the scarcity of atomic detail. A comprehensive investigation of the key rupture-stages including both unrestrained and frustrated propagation is made - characterisation of the latter leads to a first-order correction to the classical film-retraction theory.

The investigation also gives fresh insights on the very definition of surface tension and a more mechanistic view of how it acts to keep a surface intact.

Publications:
(3) Rahman et al., Communications Physics, Nature, 2024.
(2) Rahman et al., Journal of Chemical Physics, 2023.
(1) Rahman et al., Langmuir, 2022.

Capillarity Driven Building Heat Recovery

An analytical model to investigate the (non-trivial) variation of the shape of the liquid-vapor interface along the adiabatic section of a heat pipe is developed. This study pays particular attention to the case where a heterogeneous surface chemical treatment is applied to the wick to achieve an axial wettability gradient providing quantitative evidence that a heterogeneous surface chemical treatment offers performance benefits.

Software development:

Designed LowTHeR, an innovative interactive software tailored for manufacturers at Engineered Air Inc. based in Calgary, Canada. This serves as a comprehensive tool to facilitate the design, assessment, and optimization of heat pipes empowering manufacturers with enhanced decision-making capabilities.

Publications:
(2) Rahman et al., Int. J. Heat Mass Transf., 2021.
(1) Kumar et al., Applied Thermal Engineering, 2024.

Dynamics of Compound Droplets

Superior control of multiphase micro-drops owns much of the future in microfluidic technology. Understanding the dynamics of such compound systems is the key to its large-scale applications. The knowledge of the interface dynamics creates a rich profusion of domains that were previously unexplored. This study explored rolling, spreading and evaporation of such droplets.

This study employed needle-less deposition technique, high-speed imaging of spreading, surface treatments, and other sophisticated experimental methods. More details in this link.

Publications:
(4) Rahman et al., Langmuir, 2019.
(3) Rahman et al., Col. Surf. A, 2019.
(2) Rahman et al., Col. Surf. A, 2018.
(1) Rahman et al., Phys. Rev. Fluids, 2018.

"Search continuously for a better problem than the one you are working on at present. The choice of problem is the most important scientific decision you will ever make.” - Louis Brus (Nobel laureate, Chemistry, 2023)

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