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I am wondering what will be the physics to explain how two neutral, chemically nonreactive objects stick. I know that using van der Waals formalism, we can treat neutral body electrodynamic forces and arrive with attractive forces that pull the objects together.

Now, once the objects touch (say a mechanical cantiliver in a MEMS sensor like the one used in an iPhone), what happens to the forces? A quantitative answer or some estimate on how strong the attractive force is for simple cases will be very appreciated.

in response to anna's comment : Let us consider what happens in vacuum for ultra smooth surfaces, with no residual electrical charge and fully chemically stablized surfaces (example, silicon crystals with stabilised surface bonds).

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Well, atmospheric pressure also plays a role, as evidenced by all those hooks that hold on to the wall by removing the air. The problem is not well defined for a general answer, imo. – anna v Jun 25 '11 at 13:26
thanks anna. Can we consider what happens in vacuum, ignoring any atmopsheric effects. – New Horizon Jun 26 '11 at 5:27
up vote 2 down vote accepted

I will take a stab, though it needs a solid state physics background, in which I am weak.

a) in the case of crystals, as the two surfaces touch the crystal symmetry will take over with maybe some dislocation plane. i.e. the van der Waals forces will make the two one and you will not be able to easily separate them.

b) if amorphous,

1) inorganic example glass on glass, the attraction is not strong enough to create one body. The two will be separable.

2) organic surfaces with strong static fields example two cling film layers ,would adhere as one body, depending on the material .


So it will depend on the specific materials under study.

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