Controlling nanowear in a polymer by confining segmental relaxation.
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.