Sliding Friction between two Plates as a function of surface roughess

[MrDomino]

For our Manufacturing class, one of our take-home quizzes is to find out why, as surface roughness continues to decrease (think of very finely polished materials) the static friction between the plates as you try and slide them will increase. Basically, really rough surfaces will be hard to slide and really fine surfaces will also be hard to slide.

We can use any sources and the explanation must be in-depth (driven down to pretty much the molecular level).

As of now, we're having difficulty finding information and I figured some of you guys here might know where to look (we've been searching Google Scholar, Web of Science, etc.).

 

[Savant13]

The intermolecular forces are stronger if there is more area over which to act.

Let us consider a rough surface with grooves, the surface of which looks like this in cross-section:

_----_----_----_----_----_

The contact surface area between too such surface would be decreased, but the the grooves are not wide enough for the hills in between to go in them and catch.

Another possible surface would be like this:

__-__-__-__-__-__-__

When two of these surfaces are in contact, the hills of one enter the valleys of another. This results in a resistance to lateral movement. It is friction, but a different kind.