Is rubber rough because it deforms easily into the uneven surface it is in contact with, increasing the grip and so causing high friction. Please help me and tell me the most widely accepted theory.

Im gona add a strongly related question to this thread.

 

Why is rubber so bouncy?

Why is rubber so rubbery?

How is the rubber in tires so incredibly strong, yet still so rubbery?

I heard somewhere that tires have to have nitrogen put in the mix so bacteria won't eat them.

My supervisor once said, "Rubber is magic!". We produced a variety of molded rubber products, and he was a formidably competant Engineer. When asked what he meant, he cited many instances he had experienced where, during what should have been predictable engineering results, rubber had performed feats which were unexplainable! imp

How is the rubber in tires so incredibly strong, yet still so rubbery?

 

Natural rubber (unsaturated hydrocarbon) is held together by London interactions when it's unstretched. If you stretch it, the tangled coils of rubber molecules begin to disentangle and straighten in the direction of the extension.

 

The elasticity can be improved by a process called vulcanization...which was discovered (no surprises) by Charles Goodyear. The mixture was rubber, sulfur and lead oxide which he'd accidentally left on the stove. The sulfur reacts with the carbon double bonds C=C to form bridges between two carbon chains (rubber is a polymer). So when stretched, the chains can't be pulled apart, and return to their original shape. With vulcanization, rubber can be stretched over eight times it's original length...the more sulfur is added, the more rigid the rubber becomes.

 

I presume it's rough, because the rubber molecules are tangled.

 

This was covered in my chemistry module last year.

I'm not sure if you already said this in your explanation, but what part does the lead oxide take in vulcanization?

Sorry EZ, I missed your question...I had a quick google and couldn't find anything, does anybody else know why PbO is used in vulcanization ?

 

I'd hazard a guess that it helps cement the rubber, or add strength...any takers ?