Controlling nanowear in a polymer by confining segmental relaxation.

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Gotsmann, B.; Duerig, U. T.; Sills, S.; Frommer, J. and Hawker, C. J.;
Nano Lett.
6, 296-300.

Molecular relaxation of a copolymer designed for nano-electromechanical systems was chemically confined by varying the spacing between cross-links, c. A critical cross-link spacing of 1−3 nm marks a transition in the nano-mechanical properties evaluated by atomic force microscopy. The transition reveals an interplay between the cross-link spacing and the length scale for backbone relaxation, , in cooperatively rearranging regions. For c , the natural backbone relaxation process is relatively unaffected by the cross-links and a ductile, low hardness behavior results. For c < , the cross-links directly interfere with backbone relaxation and confine segmental mobility, leading to a brittle, high hardness response.