In this day and age, glass is pretty much ubiquitous.
It’s an integral part of our smartphones,
high speed fiber optic cables,
windows...the list goes on.
And yet, even though we’re surrounded by it,
scientists are still puzzled by glass, and why it forms it way it does.
Through studying glass, researchers have realized that there could be an ideal form
that may never be attainable—
but they’re still on a quest to find it.
There are more types of glass than the silica variety you’re most familiar with.
Glass is technically any rigid amorphous solid,
meaning its atoms and molecules aren’t arranged in an orderly structure,
but rather in whatever random arrangement they happened to be in
when the material cooled and solidified.
It’s as though a liquid just stopped moving all of a sudden.
Unlike ice, where the water molecules tug on each other and lock themselves into a repeating crystal pattern,
as glass cools, its molecules contract until they stop moving altogether.
And that’s weird—because in theory, if it were a liquid that has stopped flowing because it was cold,
you should be able to still give it a squeeze and change its shape.
I would not recommend you squeeze glass to give this a try, it’s rigid and it’ll cut ya.
You may have heard that because of this, glass is like an endlessly flowing liquid,
and that’s sort of true... but only in the strictest sense.
One study from 2017 estimated that if a cathedral were to stand at room temperature for a billion years,
it’s glass would flow just a single nanometer.
Another research team from Spain examined samples of 110 million-year-old amber,
a naturally occurring variety of glass derived from tree sap,
and found that over its long existence it had become about 2% denser.
Decades ago, researchers came up with an idea:
if glass could still flow and settle,
then maybe it could reach a hypothetical ideal state,
where the randomly flowing molecules happened to arrange themselves as dense and orderly as possible.
This “ideal glass” could explain why glass is a liquid with molecules that can’t flow.
But to achieve it in reality, through the usual method of cooling a liquid until it hardened,
meant cooling it impossibly, or even infinitely slowly.
This would give the molecules a chance to settle into their lowest energy arrangement.
Glass made this way would have entropy as low as a crystal’s.
Paradoxically, randomness could produce order.
Ideal glass would have properties very different from the glass we’re used to.
For one, it would have a lower heat capacity when cooled to near absolute zero.
Non-ideal glass is thought to be riddled with two-level systems,
bunches of molecules that can go back and forth between two equally stable arrangements.
Near absolute zero, even when crowded by surrounding molecules,
these two-level systems can quantum tunnel between configurations, absorbing heat in the process.
But if ideal glass is already in the most stable configuration possible,
there is no second form it can switch to, so its heat capacity drops.
Amazingly, while we haven’t found the ideal glass we’re searching for, we have gotten closer.
That’s thanks to a very different glassmaking technique that makes use of vapor deposition,
where glass is built one molecule at a time.
The result is ultra-stable glass that’s not as orderly as the hypothetical ideal,
but still denser and more stable than any glass we’ve made before.
Scientists are also searching for the perfect form of glass virtually.
Thanks to advancements in computer processing power and modeling techniques,
simulations that look for the ideal arrangement have gotten exponentially faster.
In the end, we may never be able to make ideal glass,
but we’re curious and we're diligent, and we’re going to keep trying.
You may have heard that old cathedral glass is thicker at the bottom because it’s sagged over time.
In reality, that’s just due to the technique used to make the glass.
We’re struggling to make common glass better,
but we may be able to make graphene out of common trash.
For more on that check out my episode here.
Are there any other material mysteries you’d like us to cover?
Let us know down in the comments, make sure to hit that subscribe button,
and as always, thanks for watching Seeker.
We’ll see you next time.