Publications

In press

Y. Li, M. Alipour, and A. A. Pahlavan, “Cross-streamline diffusiophoretic migration of colloids in Taylor-dispersed channel flows”, Journal of Fluid Mechanics, in press (2026); preprint.

Experiments and a model show that faint salt gradients across a narrow channel can move tiny particles between its faster center and slower edges, even when the salt appears well mixed across the channel. This sideways motion changes how particles leave the channel: a rising salt concentration helps clear them in a compact front, while a falling concentration leaves a more extended trail.

A. S. Rajput and A. A. Pahlavan, “Fluidic hysterons and memory in flow networks”, Physical Review X in press (2026). Preprint.

Flexible fibers inside tiny channels can switch between two stable shapes, changing the resistance to flow and retaining a memory of earlier forcing. Experiments and a model show how connecting these elements creates coordinated switching and history-dependent flow paths, providing a physical approach to storing and responding to information in fluid networks.

2026

Z. Chen and A. A. Pahlavan, “Biofilm density regulates diffusiophoretic colloid penetration”, Soft Matter 22, 5178–5186 (2026). Emerging Investigators Series.

Experiments in model dead-end pores show that salt gradients can help microscopic particles penetrate bacterial biofilms, but that this benefit weakens as the biofilm becomes denser. The results connect particle delivery to the structure of the bacterial community and show why the same chemical driving force can produce different outcomes as a biofilm grows.

A. Pujari and A. A. Pahlavan, “Diffusiophoretic dispersion of a colloidal blob in two-dimensional porous media”, Journal of Fluid Mechanics 1036, A5 (2026). Preprint.

Experiments and simulations track a cloud of particles released together with salt into a model porous material, where chemical gradients move particles between faster and slower flow paths. For the conditions studied, motion toward higher salt stretches the cloud and can split it into two peaks, while motion away from higher salt keeps it more compact.

Y. Li, M. Alipour, and A. Pahlavan, “Solute dispersion enhances the phoretic removal of colloids from dead-end pores”, Journal of Fluid Mechanics 1031, A19 (2026).

Experiments and a model show that a gradual increase in salt concentration can remove more particles from a dead-end pore than a sudden increase, even though removal starts more slowly. The gradual change sustains the chemical gradient for longer, revealing a tradeoff between rapid initial clearing and how many particles are ultimately removed.

M. Alipour, Y. Li, H. Liu, and A. A. Pahlavan, “Diffusiophoretic transport of colloids in porous media”, Science Advances 12, eady9874 (2026). Preprint.

Experiments and simulations show that a moving salt front can steer particles across flow paths in model porous materials, substantially changing their spreading and removal. Under the tested conditions, a front with higher salt concentration helps particles leave in a narrower, faster-clearing band, suggesting a way to control transport through chemical gradients.

A. A. Pahlavan, M. Murrell, “Active Wetting: Statics and Dynamics”, Annual Review of Condensed Matter Physics, 2026.

This review examines how living cells and tissues spread, retract, and change shape on surfaces while continuously generating their own forces. It connects these behaviors to the physics of ordinary liquid wetting and identifies the new principles needed to describe materials that consume energy and respond to their surroundings.

2025

H. Liu and A. A. Pahlavan, “Diffusioosmotic Reversal of Colloidal Focusing Direction in a Microfluidic T-Junction”, Physical Review Letters 134, 098201 (2025). Preprint. Media coverage: Yale Engineering News, Phys.org.

Experiments and three-dimensional simulations show that a salt gradient in a tiny channel junction can focus particles toward the less salty side, opposite to what their direct response to the gradient would suggest. The reversal comes from fluid motion generated along the channel walls, showing that predicting particle transport requires accounting for both the particles and their surroundings.

Dongqi Li, Zhibing Yang, Renjun Zhang, Amir A. Pahlavan, Ran Hu, Yi-Feng Chen, “Interfacial patterns of stretching suspension”, Physical Review Fluids, 2025.

Experiments and theory examine the patterns that develop when a suspension of particles is stretched against air. Small differences in particle concentration and disturbances caused by individual particles help transform a smooth boundary into waves, fingers, and branching shapes, connecting the patterns to the suspension’s microscopic structure.

Y. Qiu, L. Cueto-Felgueroso, A. A. Pahlavan, B. K. Primkulov, R. Juanes, “Phase-field modeling of two-phase displacement in a capillary tube”, Physical Review Fluids, 2025.

This study develops and tests a model of one fluid displacing another inside a narrow tube, with a boundary condition that captures how the fluids wet the solid wall. The model reproduces changes in interface shape, films left behind, and breakup observed in experiments, helping predict displacement across different surface preferences.

2024

A. A. Pahlavan, “The soil plastisphere: The nexus of microplastics, bacteria, and biofilms”, InterPore Journal 1(3), IPJ271124–2 (2024). Invited commentary; front cover.

This commentary brings together research on how water flow, chemical gradients, bacterial swimming, and biofilm growth influence microplastics in soil. It identifies physical mechanisms and open questions linking the movement of plastic particles to their colonization by microbes, providing a framework for studying these interactions in porous environments.

S. McBride, S. Atis, A. A. Pahlavan, K. Varanasi, “Crystal Patterning from Aqueous Solutions via Solutal Instabilities”, ACS Applied Materials & Interfaces, 2024.

Experiments show that evaporating calcium sulfate solutions can form ordered arrays, branches, and sawtooth crystal patterns as temperature and surface wetting change. The patterns arise from coupled liquid flows and motion of the droplet edge, and the study demonstrates that the resulting water-soluble crystals can serve as removable masks for making small surface features.

P. R. Kaneelil, J. P. de Souza, G. Turk, A. A. Pahlavan, and H. A. Stone, Electrically mediated self-assembly and manipulation of drops at an interface, Soft Matter 20, 5417–5424 (2024). Preprint.

Water droplets floating on an oil surface can organize through electrical interactions with one another and with the surrounding boundaries. Experiments show that changing the oil depth and electrical conditions controls droplet spacing and motion, offering ways to assemble, trap, and manipulate droplets at a liquid interface.

D. Li, Z. Yang, A. A. Pahlavan, R. Zhang, R. Hu, and Y-F. Chen, “Stability transition in gap expansion-driven interfacial flow”, Physical Review Letters, 2024.

Experiments and theory examine when the boundary of a liquid develops fingers as the gap between two confining plates expands. A prediction that accounts for the size of the initial disturbances explains the observed transition more accurately than one based only on whether disturbances can grow, clarifying when an apparently smooth interface becomes visibly unstable.

M. S. Yousafzai, S. Amiri, Z. G. Sun, A. A. Pahlavan, M. Murrell, “Confinement induces internal flows in adherent cell aggregates”, Journal of the Royal Society Interface, 2024.

When spreading cell aggregates reach the edge of an adhesive region, cells can move upward and back inward instead of continuing outward, creating circulation inside the tissue. Experiments and a physical model show how this internal flow follows from the balance between cell-driven spreading, surface tension, and confinement, connecting the pattern of adhesion to collective cell motion.

2023

Y. Li, Y. Chen, S. Liu, Y. Li, H. A Stone, A. A. Pahlavan, S. Granick, “Volatile droplets on water are sculpted by vigorous Marangoni-driven subphase flow”, Langmuir, 2023.

Evaporating droplets floating on water can develop fingers and branches because surface-tension differences drive strong flows in the water beneath them. Experiments show that these underlying flows can sculpt the droplet boundary and, for mixtures, promote the release of smaller droplets, revealing how the supporting liquid controls the shape above it.

B. K. Primkulov, A. A. Pahlavan, L. Cueto-Felgueroso, R. Juanes, “Motion of a viscous slug on heterogeneous surfaces: crossover from stick–slip to steady sliding”, Journal of Fluid Mechanics, 2023.

A theoretical study explains why a viscous liquid plug moving through a tube with uneven surface properties can alternate between sticking and slipping at low driving speeds, yet slide steadily at higher speeds. The model predicts the transition by tracking how resistance at the moving liquid edge competes with viscous resistance within the liquid.

L. Yang, A. A. Pahlavan, H. A. Stone, C. D. Bain, “Evaporation of alcohol droplets on surfaces in moist air”, Proceedings of the National Academy of Sciences, 2023.

Experiments and a model show that moisture in the air can reshape the evaporation of tiny alcohol droplets because water condenses into them while the alcohol evaporates. The resulting changes in composition drive internal flows and can produce flat droplets and more even particle deposits, connecting humidity to the outcome of small-scale printing and coating.

J. L. Wilson, A. A. Pahlavan, M. Erinin, C. Duprat, L. Deike, H. A. Stone, “Aerodynamic interactions of drops on parallel fibres”, Nature Physics, 2023.

Experiments show that airflow across parallel fibers can make attached droplets move along the fibers, align with neighboring droplets, repel one another, or merge. Measurements of the surrounding air reveal that interactions between droplet wakes drive these behaviors, linking fiber spacing and airflow to controlled droplet motion and coalescence.

Research Briefing. How drops of liquid move along parallel fibres in a perpendicular airflow, Nature Physics 19, 1565–1566 (2023).

This Research Briefing explains how airflow across parallel fibers makes attached droplets move along the fibers and interact through their wakes. It highlights the underlying study’s observations of alignment, repulsion, and merging, and discusses why these behaviors matter for collecting and removing droplets from fibrous materials.

Y. Qiu, K. Xu, A. A. Pahlavan, R. Juanes, Wetting transition and fluid trapping in a microfluidic fracture, Proceedings of the National Academy of Sciences, 2023.

Experiments and theory show that small variations in the walls of a model fracture change when a moving fluid leaves a film behind and how much liquid remains trapped. By connecting surface geometry to the transition between displacement and film deposition, the study explains how roughness can strongly influence fluid retention in narrow cracks.

Y. Li, A. A. Pahlavan, Y. Chen, S. Liu, Y. Li, H. A Stone, S. Granick, Oil-on-Water Droplets Faceted and Stabilized by Vortex Halos in the Subphase, Proceedings of the National Academy of Sciences, 2023.

Oil droplets floating on shallow water can develop polygonal shapes and remain separated from nearby droplets because evaporation and dissolution generate circulating flows around them. Experiments and theory show how these vortex-like flows compete with the surface tension that normally rounds a droplet, producing unusual shapes and coordinated motion among neighboring droplets.

2022

M. A. Herrada, A. Ponce-Torres, P. R. Kaneelil, A. A. Pahlavan, H. A. Stone, and J. M. Montanero, Effect of a soluble surfactant on the linear stability of two-phase flows in a finite-length channel, Physical Review Fluids, 2022.

A numerical study shows that even a small amount of soluble surfactant can accumulate near the downstream end of an interface between two flowing liquids. The resulting change in surface tension deforms the interface and makes it unstable at lower flow rates, demonstrating why trace surface-active material can alter the performance of small fluid channels.

P. R. Kaneelil, A. A. Pahlavan, N. Xue, and H. A. Stone, Three-dimensional self-similarity of coalescing viscous drops in the thin-film regime, Physical Review Letters, 2022.

Three-dimensional measurements and a thin-film model reveal how two viscous droplets resting on a surface join together as the liquid bridge between them grows. After rescaling, the evolving bridge follows a common shape in all three dimensions, bringing previously separate descriptions of droplet merging into one physical picture.

P. R. Kaneelil, A. A. Pahlavan, M. A. Herrada, K. LeRoy, K. Stengel, S. Warner, A. M. Galea, and H. A. Stone, Symmetry breaking of a parallel two-phase flow in a finite length channel, Physical Review Fluids, 2022.

Experiments and simulations show that two liquids flowing side by side through a symmetric channel can lose their symmetry near the outlet and form drops that cross into the neighboring stream. The study explains when this happens through the competition between viscous pressure and surface tension, showing how fluid properties and outlet geometry determine whether the interface remains stable.

2021

A. A. Pahlavan, L. Yang, C. D. Bain, and H. A. Stone, Evaporation of Binary-Mixture Liquid Droplets: The Formation of Picoliter Pancakelike Shapes, Physical Review Letters 127, 024501 (2021). Editors’ Suggestion; Featured in Physics.

Tiny droplets made from two alcohols can flatten into pancake-like shapes during evaporation because differences in composition create surface-tension-driven flows. Experiments and theory explain this temporary flattening and show how it can suppress the usual ring of deposited particles, producing more uniform coatings.

B. K. Primkulov, A. A. Pahlavan, X. Fu, B. Zhao, C. W. MacMinn, R. Juanes, Wettability and Lenormand’s diagram, Journal of Fluid Mechanics, 2021.

This study expands a classic map of fluid displacement in porous materials by including which liquid the solid surface prefers to contact. Pore-scale models show how that preference changes the balance among smooth invasion, branching fingers, cooperative pore filling, and flow along corners, explaining patterns that viscosity and flow rate alone cannot capture.

P. de Anna, A. A. Pahlavan, Y. Yawata, R. Stocker, R. Juanes, Chemotaxis under flow disorder shapes microbial dispersion in porous media, Nature Physics, 2021.

Experiments in model porous materials show that bacteria following chemical cues can spread differently from passive particles because their swimming changes how long they remain in slower-flowing regions. The study links these local behavioral responses to a larger-scale increase in microbial dispersion, showing that both the disorder of the flow and bacterial sensing shape transport.

2020

F. Yang, A. A. Pahlavan, S. Mendez, M. Abkarian, H. A. Stone, Towards improved social distancing guidelines: Space and time dependence of virus transmission from speech-driven aerosol transport between two individuals, Physical Review Fluids, 2020. (Editors’ Suggestion, Rapid Communication)

This 2020 modeling study examines how speech and breathing carry exhaled particles between two people facing one another without masks. It shows that exposure depends on both separation and the duration of an encounter because the exhaled cloud evolves in space and time, rather than becoming instantly mixed throughout a room.

N. B. Lu, A. A. Pahlavan, C. A. Browne, D. B. Amchin, H. A. Stone, S. S. Datta, Forced Imbibition in Stratified Porous Media, Physical Review Applied, 2020.

Experiments visualize a wetting liquid invading two connected porous layers and show a switch from preferential entry into finer pores at low flow rates to coarser pores at higher rates. A model explains this competition through capillary forces, viscous resistance, and exchange between the layers, helping predict which parts of a layered material will fill first.

B. K. Primkulov, J. Y. Y. Chui, A. A. Pahlavan, C. W. MacMinn, R. Juanes, Characterizing dissipation in fluid–fluid displacement using constant-rate spontaneous imbibition, Physical Review Letters, 2020.

An experiment using a viscous liquid plug isolates the energy lost as one fluid spontaneously displaces another at a steady rate. The results show that resistance near the moving liquid edge can account for a substantial share of the dissipation, providing a way to distinguish this local friction from resistance throughout the bulk liquid.

C. Kurzthaler, L. Zhu, A. A. Pahlavan, H. A. Stone, Particle motion nearby rough surfaces, Physical Review Fluids , 2020. (Rapid Communication)

A theoretical study shows that small-scale wall roughness can redirect a nearby moving particle and change its speed through the surrounding fluid flow, even without direct contact. For randomly rough surfaces, these variations produce differences in particle trajectories and spreading, linking microscopic surface texture to particle transport.

B. K. Primkulov, A. A. Pahlavan, L. Bourouiba, J. W. M. Bush, R. Juanes, Spin coating of capillary tubes, Journal of Fluid Mechanics, 2020.

Experiments and theory show that spinning a liquid-filled capillary tube can spread liquid into a thin, uniform coating on its inner wall. The study predicts how the film thins with time and examines how it becomes unstable after spinning stops, connecting rotation to both coating thickness and the coating’s subsequent evolution.

2019

A. A. Pahlavan, H. A. Stone, G. H. McKinley, R. Juanes, Restoring universality to the pinch-off of a bubble, Proceedings of the National Academy of Sciences, 2019.

Experiments and theory show that a bubble breaking inside a narrow tube passes through two stages whose shapes become predictable after appropriate rescaling. The first stage removes the influence of earlier details, allowing the final breakup to follow a common pattern set by the balance of viscosity and surface tension.

B. K. Primkulov, A. A. Pahlavan, X. Fu, B. Zhao, C. W. MacMinn, and R. Juanes, Signatures of fluid–fluid displacement in porous media: wettability, patterns and pressures, Journal of Fluid Mechanics 875, R4 (2019). JFM Rapids.

A pore-scale model connects the patterns formed when one fluid displaces another to the pressure needed to drive the displacement. By accounting for how individual pores fill under different wetting conditions and flow rates, the study explains both the invasion pathways and their characteristic pressure fluctuations.

2018

B. Zhao, A. A. Pahlavan, L. Cueto-Felgueroso, and R. Juanes, Forced Wetting Transition and Bubble Pinch-Off in a Capillary Tube, Physical Review Letters 120, 084501 (2018).

Experiments and theory show that increasing the speed of fluid displacement in a straight capillary tube can change a stable moving boundary into a finger that leaves a liquid film on the wall. The film can then retract and pinch off a bubble, revealing how surface wetting and flow rate can generate bubbles even without a constriction in the tube.

A. A. Pahlavan, L. Cueto-Felgueroso, A. E. Hosoi, G. H. McKinley, R Juanes, Thin films in partial wetting: Stability, dewetting and coarsening, Journal of Fluid Mechanics, 2018.

A theoretical model examines how an unstable thin liquid film breaks into droplets and how those droplets grow at the expense of smaller ones. By including molecular interactions through a film-thickness-dependent interfacial tension, the model changes predictions of the initial rupture and later droplet sizes, improving the physical description of films that only partly wet a surface.

2015

A. A. Pahlavan, L. Cueto-Felgueroso, G. H. McKinley, and R. Juanes, Thin Films in Partial Wetting: Internal Selection of Contact-Line Dynamics, Physical Review Letters 115, 034502 (2015). Featured in Physics.

This study develops a thin-film model that explains how a liquid can spread across a surface and then stop at a finite size when it only partly wets that surface. Molecular interactions between the liquid and solid determine the motion of the liquid edge within the model, connecting microscopic surface forces to the visible dynamics of spreading.

2012

B. Ezhilan, A. A. Pahlavan, D. Saintillan, Chaotic dynamics and oxygen transport in thin films of aerotactic bacteria, Physics of Fluids, 2012.

A mathematical model and three-dimensional simulations show how bacteria that swim toward oxygen can generate collective flows in thin liquid films. As the film becomes thicker, steady arrangements give way to chaotic plumes that enhance oxygen transport and consumption, linking microbial motion to the supply of a resource the cells need.

2011

A. A. Pahlavan and J. B. Freund, Effect of solid properties on slip at a fluid-solid interface, Physical Review E 83, 021602 (2011).

Molecular simulations examine how the properties of a solid wall and the way heat is removed affect the apparent slip of liquid along that wall. The results show that the treatment of heating can strongly influence predicted friction, helping distinguish physical changes in slip from effects introduced by the simulation method.

A. A. Pahlavan, D. Saintillan, Instability regimes in flowing suspensions of swimming micro-organisms, Physics of Fluids, 2011.

A theoretical study and three-dimensional simulations show that an imposed shear flow can reorganize and eventually suppress the collective instabilities of swimming microorganisms. As shear strengthens, the predicted motion passes through patterns with progressively fewer active spatial directions, connecting externally driven flow to the structure of collective swimming.