We thought it would be good to follow up on some of the issues raised
in Elizabeth's talk last week. One issue is clearly whether changes
in contact area with time are coming from subsurface plastic
deformation, changes in interfacial energy with time in contact,
capillary condensation, recoverable viscoelastic deformation, etc..
The answer may depend on the material system.
To kick off the discussion Jay Fineberg will show some hysteretic
measurements of contact area with load for PMMA that don't show
evidence of permanent plastic deformation. Then Patty McGuiggan
will show some hysteresis curves with discrete jumps that are
humidity dependent, but appear to be friction related.
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