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Van de Waals (VdW) forces are intermolecular forces that are for example, due to spontaneous polarisation effects between atoms. As far as I understand, they occur between any type of atom/molecule/material, it does not matter if it’s an insulating or conducting material, if there are filled electronic shells etc.

One often hears about these VdW forces in the context of molecules or small particles. Sometimes it is also mentioned for macroscopic objects e.g. Geckos which climb a wall.

However, also the Casimir effect is due to relativistic, retarded VdW forces. There one has two macroscopic metal plates separated by a distance. The plates will then slowly attract and get closer.

My question is:

Is there a similar effect as the Casimir effect but with non-metallic materials? Do macroscopic objects which are separated by a macroscopic distance attract each other by VdW forces (although the effect may be small)? For example: if we have two non-metallic plates floating in free space, would they eventually attract each other due to VdW forces?

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    $\begingroup$ Electric charge and magnetic forces will usually dominate in macroscopic bodies. My gut feeling is that for sufficiently "macroscopic" masses (e.g. 1kg) gravity will dominate (otherwise torsion balance experiments to determine the gravitational constant would be impossible). So... basically you would have to choose the size and mass and distances very carefully to see remnant intermolecular forces rather than something else. The gecko has, of course, "figured" out what the right scales are. They are microscopic. $\endgroup$
    – FlatterMann
    Commented Apr 5, 2023 at 7:24
  • $\begingroup$ @FlatterMann Thanks for the comment. Do you know of any experiment like that for the Casimir effect but for non metallic objects? $\endgroup$
    – Lockhart
    Commented Apr 8, 2023 at 17:15
  • $\begingroup$ Did you do a literature search? Even the Wikipedia article on the Casimir effect has more than enough pointers to experiments. If you look for citations of important papers of precision Casimir experiments, you should be able to find what you are looking for. $\endgroup$
    – FlatterMann
    Commented Apr 8, 2023 at 17:25
  • $\begingroup$ @FlatterMann I did not find anything useful on the Wikipedia page, because ‚Casimir Effect‘ only refers to the attraction of conducting plates. Not conducting plates are never mentioned. However, after some digging I found that Lifshitz did some calculations regarding this situation: web.archive.org/web/20200728132311/http://www.jetp.ac.ru/… $\endgroup$
    – Lockhart
    Commented Apr 9, 2023 at 6:52

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Yes, this type of force is also present between macroscopic surfaces provided their distance is small. The force is quantified by the Hamaker constant and can be measured by the surface force apparatus.

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  • $\begingroup$ Thank you for your answer! I looked it up and it seems that the potential between e.g. two spheres goes with 1/r. So it’s relatively long range. Shouldn’t it be observed at longer ranges (like electrostatic forces which also go like 1/r)? $\endgroup$
    – Lockhart
    Commented Apr 6, 2023 at 7:32
  • $\begingroup$ The vdW force is a very close range force. Even though its origin is electrostatic, the net effect is that it drops very fast with distance. $\endgroup$
    – Themis
    Commented Apr 6, 2023 at 10:45
  • $\begingroup$ But if I calculate the VdW force between macroscopic objects (which introduces the Hamaker constant) the potential does not fall of like $1/r^6$ anymore but for example like 1/r as for macroscopic spheres. It’s mentioned here at page 9: roma1.infn.it/~sciortif/didattica/SOFTSTRUTTURA/SOFTSTRUTTURA/… $\endgroup$
    – Lockhart
    Commented Apr 6, 2023 at 11:31
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To add to Themis answer, these forces are short ranged and quite weak. They're usually surface forces (if I recall correctly). A specific case of van der Waals force would be the London force. Cheers

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