Tracing self-regulating

Figure 8 (Left) Force spectroscopy Shear forces between poly(ethylene propylene) end functionalized with a zwitterionic group (PEP-X) brush-bearing surfaces at separation D=7.0 0.4nm. Upper trace, applied lateral motion (AXo) of top mica surface lower trace, shear force fs transmitted to the lower mica surface. The horizontal broken line represents the midpoint between the shear forces on the back and forth cycles, and is therefore the position of zero shearforce when the shear springs are unbent. Inset (i) illustrates the chain configuration in the initial force rise regime a- b. Inset (ii) illustrates the relaxation of a chain following cessation of the applied motion at point d (lower trace) the thick part is as yet unrelaxed, while the thin part has relaxed by arm retraction. (Right) The variation of the plateau normalized shearforce (kinetic normalized friction force, fnin IR, in units of pN m" ) with sliding velocity. Vs, taken from traces as on the left. The cartoons indicate schematically the effect of the self-regulation mechanism on the interpenetration zone S (see also Section 2.24.3.5). Adapted from Tadmor, R. Janik, J. Fetters, L. J. Klein, J. Phys. Rev. Lett. 2003, 91,115503. ...

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