Structural manipulation of the frictional properties of linear polymers insingle molecular layers

Manipulation of the frictional properties of self-assembled monolayers cont aining internal molecular scaffolding through subtle variations in the :,al kyl structure is demonstrated using atomic force microscopy. Photopolymeriz able diacetylene groups are incorporated within the alkyl chains of the mon olayer, resulting in noncovalent electronic interactions between diacetylen e groups, in the unpolymerized form. Under these conditions, discrete trans itions in the friction vs load curves are observed, indicating partial coll apse of the monolayer at specific loads. Subsequent photopolymerization by UV irradiation results in covalent cross-linking between molecules and-the creation of a linear conjugated polymer backbone. This significantly alters the frictional properties of the monolayers by inhibiting lateral displace ment within the monolayer. The presence of domains due to the directionalit y of the polymer backbone leads to a corresponding directionality in the fr ictional properties of the assembly that is not observed for the unpolymeri zed monolayers.