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This is really interesting, but can anyone explain the mechanism behind why this happens[1]: > At room temperature, micron-sized sheets of freestanding graphen

by dvt 5y ago

This is really interesting, but can anyone explain the mechanism behind why this happens[1]: > At room temperature, micron-sized sheets of freestanding graphene are in constant motion [1] https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.042101 https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.0...

selimthegrim 5y ago
Graphene buckles, that is in theory its lowest energy state is not flat as a sheet. This is part of the original thermodynamic arguments against graphene's existence that were disproved by finding it. I think the Mermin-Wagner theorem used to be invoked.
robbedpeter 5y ago
The graphene isn't pulled taut like a sheet pulled flat, but slightly loose, like a sheet slightly drooping, and the graphene naturally buckles and deforms. Imagine air molecules colliding with the sheet causing buckles to form, invert, or flatten out, with the deformation popping up nearby. Each time it buckles, a tiny current is generated. If it buckles in one direction, current goes one way, if it buckles in the other direction, current goes the other way. Because of quantum effects - brownian motion - no collisions have to occur, the heat going into the graphene sheet itself is enough to chaotically produce buckling, with a direct transformation of mechanical energy deformation to electricity. Heat storage is really easy. It'll be interesting to see how efficiency scales, in practice. If it exceeds modern thermoelectric performance, it's got a future, but this might get really high efficiency. The limit is the effective surface area of the graphene. Because it's solid state, it makes low temperature / shallow geothermal much more feasible. No gradient needed is the revolutionary phenomena here. It's a solid state quantum motion based electricity generator. The higher the temperature, the more rapid the brownian motion, the more power is produced. What I don't understand is what would happen if you put a bunch of these inside a highly insulated really hot cavity. The paper suggests that it doesn't cool down while generating current, but that it cools while no current is being drawn. Is that just a "wtf, nature?!" thing or is something being missed? I can't wait for this to be replicated.
- willis936 5y ago
  >No gradient needed Wouldn't the net current be zero with no gradient? We're not violating any laws of thermodynamics here.
  - tormeh 5y ago
    It's unlikely that we'll break any of them, but it's possible. One can hope, I suppose, but I wouldn't put money on it.
  - robbedpeter 5y ago
    Nope, the quantum dynamics of individual atoms of carbon cause the buckling, no gradient needed. It doesn't make macro sense. I'm leaving the door all the way open for some alternative explanation, but so far the science seems solid. It needs to be replicated and scaled up. The weird bit is the cooling while not passing current. Does the system as a whole have a tendency to cool, and why does removing energy as electricity not cool it down? Is the quantum buckling effectively separated from the heat of the system? Particles are weird.
    - gus_massa 5y ago
      You are confusing the quantum uncertainty effect with the Brownian motion. The quantum mechanics effect of the membrane make are real and produce effect like the Zero-energy point https://en.wikipedia.org/wiki/Zero-point_energy https://en.wikipedia.org/wiki/Zero-point_energy But the article is about noise caused by Brownian motion, that is a classic mechanics effect https://en.wikipedia.org/wiki/Brownian_motion https://en.wikipedia.org/wiki/Brownian_motion
      - robbedpeter 5y ago
        I guess I'm confused about the source of the buckling, then. Is it directly caused by air molecules colliding with the graphene? If that's the case, then by definition, as current is produced, energy is taken from the collisions mechanically, and temperature would decrease. Thibado says that when current is not flowing the resistor cools down, and implies that when current is flowing, it doesn't heat up. >>“People may think that current flowing in a resistor causes it to heat up, but the Brownian current does not. In fact, if no current was flowing, the resistor would cool down,” Thibado explained. “What we did was reroute the current in the circuit and transform it into something useful.” If current is produced and the system isn't extracting heat (cooling) then the energy has to come from somewhere, right? That's why I was assuming they were talking about the Brownian motion of the graphene itself. If it's just the graphene, the system would work in a vacuum. If it's air molecules then Thibado has to be wrong, or the quote was sloppy or out of context. I'm gonna reread the paper, at least.

by dvt 5y ago

selimthegrim 5y ago

Graphene buckles, that is in theory its lowest energy state is not flat as a sheet. This is part of the original thermodynamic arguments against graphene's existence that were disproved by finding it. I think the Mermin-Wagner theorem used to be invoked.

robbedpeter 5y ago

The graphene isn't pulled taut like a sheet pulled flat, but slightly loose, like a sheet slightly drooping, and the graphene naturally buckles and deforms. Imagine air molecules colliding with the sheet causing buckles to form, invert, or flatten out, with the deformation popping up nearby. Each time it buckles, a tiny current is generated. If it buckles in one direction, current goes one way, if it buckles in the other direction, current goes the other way. Because of quantum effects - brownian motion - no collisions have to occur, the heat going into the graphene sheet itself is enough to chaotically produce buckling, with a direct transformation of mechanical energy deformation to electricity. Heat storage is really easy. It'll be interesting to see how efficiency scales, in practice. If it exceeds modern thermoelectric performance, it's got a future, but this might get really high efficiency. The limit is the effective surface area of the graphene. Because it's solid state, it makes low temperature / shallow geothermal much more feasible. No gradient needed is the revolutionary phenomena here. It's a solid state quantum motion based electricity generator. The higher the temperature, the more rapid the brownian motion, the more power is produced. What I don't understand is what would happen if you put a bunch of these inside a highly insulated really hot cavity. The paper suggests that it doesn't cool down while generating current, but that it cools while no current is being drawn. Is that just a "wtf, nature?!" thing or is something being missed? I can't wait for this to be replicated.

willis936 5y ago
>No gradient needed Wouldn't the net current be zero with no gradient? We're not violating any laws of thermodynamics here.
- tormeh 5y ago
  It's unlikely that we'll break any of them, but it's possible. One can hope, I suppose, but I wouldn't put money on it.
- robbedpeter 5y ago
  Nope, the quantum dynamics of individual atoms of carbon cause the buckling, no gradient needed. It doesn't make macro sense. I'm leaving the door all the way open for some alternative explanation, but so far the science seems solid. It needs to be replicated and scaled up. The weird bit is the cooling while not passing current. Does the system as a whole have a tendency to cool, and why does removing energy as electricity not cool it down? Is the quantum buckling effectively separated from the heat of the system? Particles are weird.
  - gus_massa 5y ago
    You are confusing the quantum uncertainty effect with the Brownian motion. The quantum mechanics effect of the membrane make are real and produce effect like the Zero-energy point https://en.wikipedia.org/wiki/Zero-point_energy https://en.wikipedia.org/wiki/Zero-point_energy But the article is about noise caused by Brownian motion, that is a classic mechanics effect https://en.wikipedia.org/wiki/Brownian_motion https://en.wikipedia.org/wiki/Brownian_motion
    - robbedpeter 5y ago
      I guess I'm confused about the source of the buckling, then. Is it directly caused by air molecules colliding with the graphene? If that's the case, then by definition, as current is produced, energy is taken from the collisions mechanically, and temperature would decrease. Thibado says that when current is not flowing the resistor cools down, and implies that when current is flowing, it doesn't heat up. >>“People may think that current flowing in a resistor causes it to heat up, but the Brownian current does not. In fact, if no current was flowing, the resistor would cool down,” Thibado explained. “What we did was reroute the current in the circuit and transform it into something useful.” If current is produced and the system isn't extracting heat (cooling) then the energy has to come from somewhere, right? That's why I was assuming they were talking about the Brownian motion of the graphene itself. If it's just the graphene, the system would work in a vacuum. If it's air molecules then Thibado has to be wrong, or the quote was sloppy or out of context. I'm gonna reread the paper, at least.