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Am I missing something? The article directly says > Researchers have used this physical phenomenon to float invisible aerosols and sort particles in microflui

Am I missing something? The article directly says > Researchers have used this physical phenomenon to float invisible aerosols and sort particles in microfluidic devices. But they have never before moved an object big enough to grasp—much less lifted anything that can carry objects itself. But radiometers have existed for decades... https://en.wikipedia.org/wiki/Crookes_radiometer https://en.wikipedia.org/wiki/Crookes_radiometer

deleted 5y ago
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colanderman 5y ago
Radiometer is a heat engine utilizing air currents... (i.e. EM radiation -> heat -> airflow -> force)... the phenomenon in the article seems to be direct conversion of EM radiation into force. "Direct photophoresis is caused by the transfer of photon momentum to a particle by refraction and reflection." [1] [1] https://en.wikipedia.org/wiki/Photophoresis https://en.wikipedia.org/wiki/Photophoresis
- JPLeRouzic 5y ago
  From the article you link, photophoresis looks similar to the classical explanation of a Crookes radiometer. The existence of this phenomenon is owed to a non-uniform distribution of temperature of an illuminated particle in a fluid medium. It cites the radiometer: Just like in Crookes radiometer, light can heat up one side and gas molecules bounce from that surface with greater velocity, hence push the particle to the other side. Yet the article seems to contradict itself: This force depends on light intensity and particle size but has nothing to do with the surrounding medium
  - Animats 5y ago
    Actual article.[1] This gives more of a sense of the required conditions. This apparently works in the 1-12 pascal range of pressure. Earth is around 100,000 pascals at sea level, and even Mars is around 600pA. This might be useful for keeping low earth orbit satellites going. Is the effect powerful enough for that? Could a microsat with solar panels generate enough thrust to equal the drag from the near space atmosphere? [1] https://www.science.org/doi/10.1126/sciadv.abe1127 https://www.science.org/doi/10.1126/sciadv.abe1127

deleted 5y ago

[deleted]

colanderman 5y ago

Radiometer is a heat engine utilizing air currents... (i.e. EM radiation -> heat -> airflow -> force)... the phenomenon in the article seems to be direct conversion of EM radiation into force. "Direct photophoresis is caused by the transfer of photon momentum to a particle by refraction and reflection." [1] [1] https://en.wikipedia.org/wiki/Photophoresis https://en.wikipedia.org/wiki/Photophoresis

JPLeRouzic 5y ago
From the article you link, photophoresis looks similar to the classical explanation of a Crookes radiometer. The existence of this phenomenon is owed to a non-uniform distribution of temperature of an illuminated particle in a fluid medium. It cites the radiometer: Just like in Crookes radiometer, light can heat up one side and gas molecules bounce from that surface with greater velocity, hence push the particle to the other side. Yet the article seems to contradict itself: This force depends on light intensity and particle size but has nothing to do with the surrounding medium
- Animats 5y ago
  Actual article.[1] This gives more of a sense of the required conditions. This apparently works in the 1-12 pascal range of pressure. Earth is around 100,000 pascals at sea level, and even Mars is around 600pA. This might be useful for keeping low earth orbit satellites going. Is the effect powerful enough for that? Could a microsat with solar panels generate enough thrust to equal the drag from the near space atmosphere? [1] https://www.science.org/doi/10.1126/sciadv.abe1127 https://www.science.org/doi/10.1126/sciadv.abe1127