Jeff,
If by "length" you mean distance between bodies, the long range van der
Waals forces scale with distance^-4. If the bodies are close enough,
short range van der Waal forces take over, which scale with distance^-3.
The transition from short to long range forces for silicon dioxide
surfaces is at a distance of about ~25nm.

Michael P.

The MEMS Exchange

Jeff Zahn wrote:

>
> Does anyone know the theoretical background on why the
> forces scale as length^1/4?
>
> Thanks,
>
> Jeff
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