porosity

A raindrop falls on glass and flattens into a pancake. Add a bit of polymer to the water, and it becomes elastic, like jelly. You'd think such a jelly would spread differently.

In a pot of boiling water, steam bubbles appear and disappear — a similar struggle takes place in two-dimensional materials. Here, electrons both create magnetism and try to extinguish it.

The brain self-cleans its waste: cerebrospinal fluid flows through narrow channels surrounding arteries. The channel walls are soft and ripple with each pulse, and the tissue is porous like a sponge. Every heartbeat turns arteries into tiny pumps, driving fluid through the pores.

In the brain's white matter, the signal travels along axons — long neuronal processes wrapped in an insulating myelin sheath. Water fills the space inside axons and outside, in the narrow gaps between fibers.

Soil is not a solid sponge but a labyrinth of pores of various sizes. After rain, water does not fill them all at once: first the narrowest ones, then the wider ones. Physicists built a theory of this process based on a simple image — a set of communicating vessels.

An ocean current hundreds of kilometers wide lives its own life, fed by energy from tiny eddies. Something similar happens in the atmosphere: small swirls pass their power on to huge air currents. This process, the inverse energy cascade, has been known for a long time.

Quantum matter rarely treats us to the spectacle of self-motion. Where the classical world teems with starling murmurations, fish schools, and bustling bacteria, quantum thermodynamics long remained serene.

Why do some systems, from gene networks to air travel, preserve imprints of the past longer than others? For a long time, network science blamed topology: the number of connections, modularity, spectrum. But two networks with the same skeleton can remember and forget in completely different ways.

Spacetime is like a giant sheet of paper. Fold it, and distant corners come together. Poke a pencil through, and you get a wormhole, a short tunnel through the folds. But the paper wants to spring back flat, snapping the passage shut. To keep it open, you need a rare “gasket”—matter with negative energy.

Millions of cilia, thin hairs, work inside the tiny ducts of our bodies. They beat in synchrony, like the oars of a galley, pushing viscous mucus or fluid along. The authors of a new study propose viewing the ciliary carpet as an active porous medium — something like a sponge that squeezes and releases itself, driving water through.

A drop of thick shampoo falls into water and freezes into a strange rope. A liquid that both flows and springs back is called viscoelastic. In it, tiny particles under ultrasound behave quite differently than in water. Viscoelasticity is a material's ability to both spread like honey and return to shape like rubber.

When you squeeze ketchup out of a bottle, you're battling its stubbornness: it sits still at first, then suddenly shoots out in a blob. That's typical non-Newtonian behavior — resistance to flow changes with how hard you push. But the authors of a new study found a way to almost completely eliminate that resistance.

A porous implant filled with a drug works like a sponge that slowly releases the substance into the surrounding fluid. But if the fluid flows quickly, it washes out the drug differently than in a calm environment. The authors computed on a computer how different flow rates and properties of the porous structure affect drug release.

A raindrop falls into a puddle, and the impact sends up a little fountain of fine spray. Each of those droplets is a new, secondary drop. How many there are, how big they are, and how long they live depend on a host of factors: the fall speed, the drop size, the properties of the water. Scientists set out to make sense of this chaos using computer simulations.

In porous materials (soil, rocks, filters) fluids move through tiny, winding channels. When two immiscible fluids, such as water and air, are present simultaneously, their interface constantly shifts: air bubbles push water out of some pores and open paths through others.

In a narrow gap between two plates, water from humid air collects on its own: this is capillary condensation. If the gap is only a few nanometers wide, water no longer behaves like a continuous liquid: every molecule counts.

Inside the kidneys, liver, and other organs, fluid flows through channels that squeeze and release like a hose underfoot. The walls of these channels are not rigid: they are porous, elastic, and soaked with moisture.

A rod stuck into a granular material (say, sand or a layer of small beads) behaves quite differently from what you might expect. Instead of going straight down, it quickly tilts away from the vertical and ends up lying flat. That's what researchers found when they dropped rigid and flexible rods into a two-dimensional layer of foam beads and tracked their motion with a high-speed camera.

A drop of oil in water, coated with soap molecules, behaves differently from a bare drop. Soap molecules are tiny rods: one end loves water, the other loves oil. In a quiescent fluid, they stand on the surface like a picket fence, lowering the surface tension — the force that pulls the drop into a sphere.

The tear film on the eye is an ultrathin layer of fluid that protects the cornea and keeps vision sharp. It’s usually pictured as a perfectly smooth surface, but the real cornea, even a healthy one, is covered in microscopic bumps.

The Sun drives the water cycle, and rain returns it to the ground. But now, every drop is a tiny hammer striking the surface. Floating plastic particles (microplastics, mostly carbon) upon impact jump up like popcorn kernels on a hot skillet. But instead of popping, they get wrapped in a thin water film and turn into weightless beads.

A drop of water with tiny particles dries on a table. The water evaporates, leaving the particles behind, and they arrange into a pattern, like sand after the tide. But if the particles are soft, the pattern turns out quite different. Researchers studied this process under a microscope, varying only one property of the particles: their elasticity.

The layer of cells lining internal organs is like a crowd in a packed subway: everyone stands shoulder to shoulder, but sometimes the crowd starts to flow, and people slip past each other. Biologists call this behavior a transition from a jammed, solid state to a fluid one.

Felt looks like a tangled ball of wool, but under X-rays you can see hidden trails inside. When a water drop lands on such material, it doesn't just spread across the surface — some of the liquid dives deep, like water into blotting paper. Scientists captured this process for the first time with an X-ray camera snapping hundreds of frames per second. The secret lies in the needles.

A bacterium swims like a tiny motorboat with a propeller — except its propeller is a long flagellum that rotates and pushes the body forward. But the body doesn't move in a straight line; it sways like a bobber on a wave. This swaying isn't random: it's part of the mechanics of motion. Until now, such swaying was studied in still water.

Drop honey onto a sponge. It lazily creeps, avoiding the voids. But if the honey becomes thinner under pressure, the flow gets trickier. Liquid with variable thickness in an uneven labyrinth of pores — a problem that had defied calculation. The authors of the new work averaged the chaos of microchannels into simple equations.