For decades, scientists believed all plastics shared one unavoidable weakness: no matter how dense or strong, gases could always slip through. Even the toughest polymers, from bulletproof Kevlar to everyday food packaging, may look solid, but at the molecular level, tiny gas molecules can still sneak through. That’s why potato chips go stale and packaged food loses its crispness.
Now, a collaboration between researchers at Boston University’s College of Engineering, MIT, the University of Texas at Austin, the University of Massachusetts and the National Institute of Standards and Technology, has overturned that assumption. In a study published today in Nature, the team reports the discovery of the first polymer that is molecularly impermeable; a man-made material that acts as a perfect barrier to gas molecules.
Scott Bunch, Associate Professor of Mechanical Engineering, Materials Science Engineering, and a faculty with BU Photonics Center, was the co-senior author of the study. Additional BU co-authors include Professor Kamil Ekinci (ME, MSE), Hagen Gress (PhD from ENG), mechanical engineering student Kaan Altmisdort.
The key is a new class of materials called two-dimensional polyaramids, or 2DPA-1. Unlike conventional plastics, which are built from long, spaghetti-like chains, these polymers grow in atomically thin sheets. When stacked, the sheets pack so tightly together they leave no gaps for molecules to sneak through.
A film of 2DPA-1, just a few nanometers thick, about 1,000 times thinner than a human hair, can trap gases inside tiny microwells for over three years without a single detectable leak. That corresponds to a gas permeability at least 10,000 times lower than any known polymer.
Strong and flexible
But impermeability is only part of the story. The films are also flexible, making them easy to process. They can be spin-coated onto surfaces like paint. In one demonstration, the researchers applied a layer of 2DPA-1 onto fragile solar cell materials. The coating extended the solar cells’ lifetimes more than 14 times, protecting them from oxygen and moisture degradation.
The films also act like tiny drumheads, vibrating millions of times per second when suspended over microscopic wells. This performance rivals graphene, the celebrated wonder material, and hints at applications in ultra-sensitive sensors and nanomechanical devices.
“This material marries the best of two worlds,” said Bunch. “By combining graphene-like impermeability with the easy processing of a polymer, this ultrathin coating could protect some of today’s most sensitive electronics — from flexible OLED screens and perovskite solar cells to wearable sensors and emerging quantum chips. It forms an invisible, molecularly tight seal that keeps out air and moisture without adding weight or stiffness. And as with many scientific discoveries, the most impactful applications of these materials may be the ones we haven’t even imagined yet.”