I am studying material physics.
I heard in the class that every adhesion or bonding can occur only with frictional force.
Today, I tried to find a proper reference for this statement but I could not.
Is there any reference that every adhesion or bonding(esp. Injective moldings) can occur only with frictional force?
Or is there any way that can happen without frictional force?
For example, in the process of molding, when melted materials harden, why does it stick to the other material? How does the frictional force acts in this case?
I want some references regarding these.