Diamond-Like Carbon: A Surface for Extreme, High-Wear Environments

Abstract

In this study, we present an in-depth characterization of a diamondlike carbon (DLC) film, using a range of techniques to understand the structure and chemistry of the film both in the interior and particularly at the DLC/air surface and DLC/liquid interface. The DLC film is found to be a combination of sp 2 and sp 3 carbon, with significant oxygen present at the surface. The oxygen seems to be present as OH groups, making the DLC somewhat hydrophilic. Quartz-Crystal Microbalance (QCM) isotherms and complementary neutron reflectivity data indicate significant adsorption of a model additive, bis(2ethylhexyl) sulfosuccinate sodium salt (AOT) surfactant, onto the DLC from water solutions and indicate the adsorbed film is a bilayer. This initial study of the structure and composition of a model surfactant is intended to give a clearer insight into how DLC and additives function as antiwear systems.■ EXPERIMENTAL SECTION Materials. Deuterium oxide (D 2 O) was obtained from Sigma (>99% purity, >99.9% D atom). Ultrapure water (UPW18.2 MΩ cm)