All Research

Nanorheology of interfacial water during ice gliding

Physical Review X·
Read the paperDOI: 10.1103/PhysRevX.9.041025

TL;DR

Imagine you're trying to slide a tiny bead across an ice cube. Scientists always assumed the reason it slides easily is because a thin layer of regular water forms underneath it. These researchers built a super-sensitive machine to actually 'feel' that water layer with a tiny bead. They discovered it's not like normal water at all. Instead, it's a 'visco-elastic' fluid, meaning it's thick and gooey, almost like honey, but also springy. This gooey-but-springy nature is the real secret to ice's slipperiness. They also found that if you coat the bead with a water-repellent material, like wax on a ski, it makes this water layer less gooey, which surprisingly reduces friction even more.

The slipperiness of ice is an everyday-life phenomenon which, surprisingly, remains controversial despite a long scientific history. The very small friction measured on ice is classically attributed to the presence of a thin self-lubricating film of meltwater between the slider and the ice. But while the macroscale friction behavior of ice and snow has been widely investigated, very little is known about the interfacial water film and its mechanical properties. In this work, we develop a stroke-probe force measurement technique to uncover the microscopic mechanisms underlying ice lubrication. We simultaneously measure the shear friction of a bead on ice and quantify the in-situ mechanical properties of the interfacial film, as well as its thickness, under various regimes of speed and temperature. In contrast with standard views, meltwater is found to exhibit a complex visco-elastic rheology, with a viscosity up to two orders of magnitude larger than pristine water. The non-conventional rheology of meltwater provides a new, consistent, rationale for ice slipperiness. Hydrophobic coatings are furthermore shown to strongly reduce friction due to a surprising change in the local viscosity, providing an unexpected explanation for waxing effects in winter sports. Beyond ice friction, our results suggest new avenues towards self-healing lubricants to achieve ultra-low friction.

  • 1Developed a stroke-probe force measurement technique to study ice lubrication.
  • 2Measured shear friction and mechanical properties of interfacial water film.
  • 3Found meltwater exhibits complex visco-elastic rheology with high viscosity.
  • 4Hydrophobic coatings reduce friction by changing local viscosity.
  • 5Results suggest new avenues for self-healing lubricants.
Science News

M87's black hole flipped its magnetic field

Imagine a bar magnet with a north and south pole. Now imagine that magnet suddenly flipping so north becomes south and vice versa. That's essentially what happened with the magnetic field around the giant black hole at the center of galaxy M87 — except this black hole is 6.5 billion times heavier than our Sun. Scientists noticed this flip by watching the powerful beam of energy, called a jet, that shoots out from the black hole. The direction and behavior of that beam changed in a way that revealed the magnetic field had reversed. It's a big deal because those magnetic fields are thought to act like the engine that powers and steers these cosmic jets, and we've rarely caught one flipping in action.

Scientific American·

The 2026 World Cup's grass is an engineering problem

Imagine you're trying to play soccer in 16 different places across the United States, Canada, and Mexico — some in freezing cold, some blazing hot, some in stadiums with roofs that block sunlight. Half of those stadiums normally use fake grass. Now FIFA, the organization that runs the World Cup, wants every single pitch to feel and play exactly the same way, like a video game where every level has identical physics. To do that, they hired grass scientists — yes, that's a real job — who figured out how to grow special grass on thin mats with plastic underneath so it can be transported like a carpet, stitched with synthetic fibers so it doesn't rip when players sprint and tackle, and tested by literally shooting balls at it with a cannon to make sure it bounces right. Different grass species are used depending on whether a stadium is hot, cool, or dark. It's basically a giant, living, high-tech floor installation that has to survive the world's best athletes running on it.

Nature Genetics·

Non-Mendelian inheritance of DNA methylation patterns in mice

Imagine your DNA is like a huge book of instructions. Mendel's laws are the normal rules for how chapters of that book get passed from parents to children. But there's also a layer of sticky notes on top of the book—called epigenetic marks—that tell cells which chapters to read and which to ignore. This study found that most of the time (about 93%), these sticky notes follow the normal inheritance rules. But about 7% of the time, they do something unexpected: new patterns appear that neither parent had, or a mark from one parent somehow silences the same mark from the other parent (called paramutation), or males and females end up with completely different sticky notes even when they inherit the same DNA. Scientists discovered this by using a new ultra-precise DNA reading technology in mice, and it opens the door to understanding hidden layers of how traits—and possibly diseases—are passed down through generations.

New England Journal of Medicine·

Digital twin–guided ablation for ventricular tachycardia

Imagine your heart is a city, and ventricular tachycardia is like a traffic jam caused by a broken road — electrical signals get stuck going in circles instead of flowing properly, causing the heart to beat dangerously fast. Doctors can fix this by burning away the broken road using a procedure called ablation. The problem is, finding the exact broken road inside a beating heart is like navigating a city you've never visited before, while driving, in the dark. What these researchers did is take detailed MRI pictures of each patient's heart, build a 3D computer copy — a 'digital twin' — and then simulate where the electrical problem was happening inside that virtual heart. They tested their fix on the computer model first, figured out exactly where to go, and THEN performed the real procedure. What used to take three hours of exploratory surgery was done in about 30 minutes, because the doctors already had a GPS map before they started.