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, δ 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, ξ α, in cooperatively rearranging regions. For δ c ≫ ξ α, the natural backbone relaxation process is relatively unaffected by the cross-links and a ductile, low hardness behavior results. For δ c ≫ ξ α, the cross-finks directly interfere with backbone relaxation and confine segmental mobility, leading to a brittle, high hardness response. © 2006 American Chemical Society.