Contact deformation behavior modes

The deformation mechanisms in various polyolefins have been studied in great detail. Kravchenko and co-workers have reported on the deformation behavior of elastomeric PP, for which the orientation and deformation of lamellae during tensile testing could be followed with high resolution using intermittent contact mode SFM (175). 

In functioning machinery the contacting parts repeatedly rub one another many times. The interaction of two surfaces on reiterated contact will in part depend on the condition in which the previous iteration left them. Under ordinary circumstances, with the machinery operating satisfactorily, each iteration is much like the one before and an analysis of steady-state wear or friction can be made on the basis of one cycle of surface interaction. Generally in such cases, but not necessarily always, asperity deformation is elastic rather than plastic. Whether an adhesive junction forms depends on the condition of the asperity surface. If the materials f>e.n. 4e are easily adhesive but the surfaces are covered by a film which inhibits adhesion, then to initiate adhesion obviously the film must first be removed, broken up or penetrated. The subsequent course of adhesive contact will then be governed by such factors as the size of the contact, the shape of the asperity, the impressed load, the strength of the material, etc., in accordance with the fundamental modes of behavior. 

In contact mode AFM, where the normal force is the detected signal, there can also be a large contribution from lateral or shear forces. These can be significant enough so as to lead to deformation, abrasion and wear. These are generally not desired, however, this behavior has been used to probe the role of chain entanglements in polystyrene films as a function of molecular weight [119]. 

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