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Unimpeded permeation of water through helium-leak-tight graphene-based membranes

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Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#11

Post by MisterTea »

hexator wrote: post #2

Can we get a simpler overview of what this means for a layperson?

At my work we use a gizmo called a helium mass spectrometer leak detector. We use it to test the hermetic seal of a welded part. It pulls a vacuum on a part or chamber and we spray helium at it and the machine looks for helium leaking through.

The units are weird: atm-cc/sec or torr liters/sec. 1x10-6 torr/liters sec is the limit for a crack large enough to let water through. Most customers require 1x10-7 or better depending. Some really exotic stuff that goes into satellites must seal to 1x10-9 or better. So helium is really small and sneaks past "holes" water and even other gases would not penetrate.

Helium, like hydrogen are really small and can penetrate many common materials, even metal (see hydrogen embrittlement). They're also difficult to remove from a vacuum chamber and even bounce backwards through high vacuum pumps. This is actually used in the leak detector and they measure this "reverse flow" of helium through the turbo vacuum pump into the mass spectrometer. Helium don't give a fuck.

So knowing that helium is really tiny and penetrates lots of things that big fat bulky water cant means this material exhibits exotic properties that are the complete opposite of what we normally observe. That's really interesting for sure.

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#12

Post by msandford »

twawaaay wrote: post #7
msandford wrote: post #3

Earlier quoted context omitted.

It makes me excited that there might be some kind of new science that could mean low power desalination.

No, it can't. Desalination by reverse osmosis requires certain force to push water through the filters which is dictated by osmotic pressure. It is unavoidable. To imagine it, think about it this way: to overcome osmotic pressure you only need to pump the water above the filter to a certain height. The height you need is only dictated by the magnitude of the pressure and not the filter. And as the water flows, you on…

You'll note, I hope, that I said "new science" which might mean such a thing is possible. Yes I agree that osmotic pressure is the thing you have to overcome. Unless somehow there's some new understanding of the world that supersedes our knowledge of osmotic pressure.

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#13

Post by twawaaay »

msandford wrote: post #12
twawaaay wrote: post #7

Earlier quoted context omitted.

No, it can't. Desalination by reverse osmosis requires certain force to push water through the filters which is dictated by osmotic pressure. It is unavoidable. To imagine it, think about it this way: to overcome osmotic pressure you only need to pump the water above the filter to a certain height. The height you need is only dictated by the magnitude of the pressure and not the filter. And as the water flows, you on…

You'll note, I hope, that I said "new science" which might mean such a thing is possible. Yes I agree that osmotic pressure is the thing you have to overcome. Unless somehow there's some new understanding of the world that supersedes our knowledge of osmotic pressure.

This "new science" would have to disprove everything we know about thermodynamics. No, not possible in the regular sense of the world.

Sure, we might find everything we know about physics is wrong but if this happens it will most likely serve to explain why things behave certain way rather than give us superpowers to ignore thermodynamics.

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#14

Post by dieselgate »

emmelaich wrote: post #10
dieselgate wrote: post #5

Earlier quoted context omitted.

It sort of seems like a bag that can hold a small object, like a golf ball, but something larger like a watermelon would "fall through" the bag without it tearing/breaking. Pretty interesting stuff but I'm not too aware of the research field, just live in a place that's wet.

In particular[0], the bigger stuff (water) blocks the smaller. > Diffusion of other molecules is blocked by reversible narrowing of the capillaries in low humidity and/or by their clogging with water. So in the absence of the water, the He would escape. [0] heh

indeed thanks for specifying

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#15

Post by jojobas »

twawaaay wrote: post #7
msandford wrote: post #3

Earlier quoted context omitted.

It makes me excited that there might be some kind of new science that could mean low power desalination.

No, it can't. Desalination by reverse osmosis requires certain force to push water through the filters which is dictated by osmotic pressure. It is unavoidable. To imagine it, think about it this way: to overcome osmotic pressure you only need to pump the water above the filter to a certain height. The height you need is only dictated by the magnitude of the pressure and not the filter. And as the water flows, you on…

Current seawater desalination technology runs at about 2x the osmotic pressure power consumption, the current membranes require quite some pressure to push even pure water through.

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#16

Post by mensetmanusman »

pmayrgundter wrote: post #4
hexator wrote: post #2

Can we get a simpler overview of what this means for a layperson?

Helium is very hard to store since it's a noble gas and so monatomic; I think it's smaller even than H2. So storing it (and H2 for that matter) is hard. Strangely, their material is able to do that while also passing water, H20, which is a much larger molecule. They suggest in the summary that there's more going on than just the size of the porosity. Haven' read more. Maybe someone else will know how useful this is f…

The kinetic diameter of water is smaller than helium because its polar nature allows it to adsorb and diffuse across solid surfaces.

This behavior helps it fit through small holes better than helium can.

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#17

Post by netr0ute »

twawaaay wrote: post #13
msandford wrote: post #12

Earlier quoted context omitted.

You'll note, I hope, that I said "new science" which might mean such a thing is possible. Yes I agree that osmotic pressure is the thing you have to overcome. Unless somehow there's some new understanding of the world that supersedes our knowledge of osmotic pressure.

This "new science" would have to disprove everything we know about thermodynamics. No, not possible in the regular sense of the world. Sure, we might find everything we know about physics is wrong but if this happens it will most likely serve to explain why things behave certain way rather than give us superpowers to ignore thermodynamics.

> No, not possible in the regular sense of the world.

How do you know that?

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#18

Post by igravious »

twawaaay wrote: post #7
msandford wrote: post #3

Earlier quoted context omitted.

It makes me excited that there might be some kind of new science that could mean low power desalination.

No, it can't. Desalination by reverse osmosis requires certain force to push water through the filters which is dictated by osmotic pressure. It is unavoidable. To imagine it, think about it this way: to overcome osmotic pressure you only need to pump the water above the filter to a certain height. The height you need is only dictated by the magnitude of the pressure and not the filter. And as the water flows, you on…

“We attribute these seemingly incompatible observations to a low-friction flow of a monolayer of water through two-dimensional capillaries formed by closely spaced graphene sheets. Diffusion of other molecules is blocked by reversible narrowing of the capillaries in low humidity and/or by their clogging with water.”

I'm having trouble parsing this.

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#19

Post by twawaaay »

jojobas wrote: post #15
twawaaay wrote: post #7

Earlier quoted context omitted.

No, it can't. Desalination by reverse osmosis requires certain force to push water through the filters which is dictated by osmotic pressure. It is unavoidable. To imagine it, think about it this way: to overcome osmotic pressure you only need to pump the water above the filter to a certain height. The height you need is only dictated by the magnitude of the pressure and not the filter. And as the water flows, you on…

Current seawater desalination technology runs at about 2x the osmotic pressure power consumption, the current membranes require quite some pressure to push even pure water through.

Of course. You want a high enough water flow to get the installation to filter lots of water. You have to have pressure above osmotic pressure. You can increase the flow of water through filter either by increasing pressure or by adding more filters.

Re: Unimpeded permeation of water through helium-leak-tight graphene-based membranes

#20

Post by twawaaay »

netr0ute wrote: post #17
twawaaay wrote: post #13

Earlier quoted context omitted.

This "new science" would have to disprove everything we know about thermodynamics. No, not possible in the regular sense of the world. Sure, we might find everything we know about physics is wrong but if this happens it will most likely serve to explain why things behave certain way rather than give us superpowers to ignore thermodynamics.

> No, not possible in the regular sense of the world. How do you know that?

Because osmotic pressure is a result of thermodynamics.
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