Research

We study the physics of complex fluids, soft materials, and living systems: how they move, deform, and organize in their surroundings. Our systems range from microscopic particles and bacterial communities to freezing soils and networks that transport fluid. We ask how flow, forces, and chemical signals interact with a material’s structure—and how that structure, in turn, changes transport.

Biological systems motivate many of these problems: organisms must sense their surroundings, exchange resources, and adapt while constrained by fluid flow and mechanics. We combine microfluidic and tabletop experiments, quantitative imaging, simulations, and theory to uncover the physical processes at work. Controlled laboratory models let us connect small-scale interactions to the behavior of natural and engineered systems.

Explore our projects: Particle transport · Biofilms · Microbial motion · Freezing and thawing · Adaptive flow networks

Chemical gradients and particle transport

Particles carried by water encounter a maze of pores in soils, filters, and biological materials. Their journeys also depend on dissolved chemicals. When salt concentration varies from place to place, the resulting chemical gradient can drive particles through the surrounding liquid—a process called diffusiophoresis.

In miniature porous materials, we show that this small additional motion can move particles between fast and slow flow paths, strongly changing travel times and spreading. How the gradient is created matters: an advancing salt front can concentrate particles, while a particle cloud released together with salt can stretch and split. In dead-end pores, a gradual salt change can remove more particles than an abrupt one under the conditions tested because the driving persists longer.

We study how chemical fields, flow, and pore geometry work together to control transport. These laboratory results motivate questions about particle delivery and removal in more complex, three-dimensional and reactive environments.

Conceptual illustration of particle paths shifting across water streamlines between solid pillars in a porous material.

Salt gradients can shift particles between flow paths. Conceptual illustration.

Selected papers

Phoretic transport in motion

Watch particles weave through a porous landscape in Chaotic Voyage of Colloids Through Salty Waters, our November 2024 APS DFD Gallery of Fluid Motion entry.

Particle delivery into biofilms

A biofilm is a microbial community embedded in a polymer-rich matrix. This living material can impede the transport of particles and dissolved substances, while its growth changes the environment through which they move.

We grow biofilms in small dead-end pores and use salt gradients to drive particles into them. As the biofilm accumulates, this chemical assistance weakens. Among the two particle sizes tested, the larger particles penetrate farther because their stronger response to the gradient outweighs their greater size.

The result shows why particle size, surface chemistry, and the structure of the living barrier must be considered together. We seek to understand the physical limits on delivery into microbial communities and how growth and transport shape one another.

Biofilm density regulates diffusiophoretic colloid penetration · Soft Matter 22, 5178–5186 (2026).

Gold particles enter a dead-end pore containing a pale biofilm matrix and rod-shaped bacteria; labels show salt-gradient-driven delivery.

Salt gradients help drive particles into a microbial matrix; the structure of that matrix affects penetration. Conceptual illustration.

Microbial motion in changing environments

Bacteria live in environments where nutrients are unevenly distributed and fluid flow continually reshapes chemical cues. Through chemotaxis, swimming cells sense and respond to those cues. Unlike a passive particle drifting in a salt gradient, a bacterium uses a biological sensing and adaptation system to guide its motion.

Our work shows that chemotaxis and disordered flow together shape how bacteria spread through porous media. We ask when sensing helps cells reach new regions, when it favors their retention in sheltered pores, and how these outcomes depend on the lifetime of chemical cues.

The environment also responds to the organisms: cells consume and release chemicals, modifying the fields they sense. Understanding this feedback connects individual behavior to transport and organization in microbial communities.

Chemotaxis under flow disorder shapes microbial dispersion in porous media · Nature Physics (2021).

Conceptual illustration of bacteria near a nutrient plume carried downstream by fluid flow; arrows show the flow direction.

Chemotaxis in flow: bacteria respond to a nutrient plume carried downstream. Conceptual illustration.

Freezing and thawing in complex environments

When soil freezes, growing ice rearranges grains, redirects remaining liquid, and changes how forces travel through the ground. We use transparent models of soil, controlled freezing, microscopy, and physical theory to watch these microscopic changes and ask which persist after thawing.

A central focus is the frozen fringe, a region where ice, sediment, and unfrozen water coexist. We ask how its water pathways open or close, how pressure affects ice growth, and how freezing history changes drainage and mechanical response. These questions connect microscopic physics to the stability of soils and permafrost and to friction beneath glaciers, where water pressure and sediment strength influence sliding.

We aim to understand how the evolving liquid spaces affect microbial transport and survival during freeze–thaw cycles, and how microbes interact with growing ice. The same ice–particle interactions are relevant to freeze casting, which uses growing ice as a template for porous materials. Our goal is to uncover shared physical principles across these natural and engineered systems.

Three layers show glacier ice, a frozen fringe containing soil grains, ice and liquid water, and unfrozen water-filled soil below.

Beneath some glaciers, the frozen fringe contains ice, sediment, and unfrozen water. Conceptual illustration.

Adaptive flow networks, memory, and physical computation

Living networks transport resources while their surroundings change. Fungi explore soil and exchange nutrients with plant roots; slime molds continually reshape their tubes. Blood microvessels adjust to local tissue demands, while roots and vascular networks support growing plants. These systems coordinate transport without a central nervous system directing every branch.

Local responses are coupled across the network: changing one route can redistribute flow elsewhere, because fluid entering, leaving, and stored within the system must balance. We ask how this interaction between structure and flow enables adaptation, retains a record of past conditions, and produces coordinated responses to changing environments.

We build simple fluidic networks to uncover the underlying physics. In our experiments, an elastic fiber inside a small channel bends with the flow and changes how easily fluid passes. This feedback lets the same imposed flow support two different fiber configurations, selected by the flow’s history. Connecting these elements changes how they switch together.

This demonstrated physical memory is a starting point. Inspired by living networks and mechanical metamaterials, we now ask whether interactions among many elements can support physical computation—processing information through changes in flow and structure—and decision-making, such as selecting routes as conditions change. Adaptation, learning, and reliable computation are research questions we are pursuing.

Fluidic hysterons and memory in flow networks · Physical Review X, accepted August 2026 (in press). Read the open preprint.

A fungal-inspired transport network connects roots and soil resources. After demand changes, some routes thicken and flow redistributes.

Living networks inspire our questions about adaptation, history, and computation in fluidic systems. Conceptual illustration.

Connect with the lab

For students, collaborators, and research program discussions, contact Amir Pahlavan. Our Join the Lab page explains how to start a conversation, and SoFLivMat seminars bring together researchers across Yale and beyond.