Tribology of non-wetting fluorinated mesoporous silica films

Abstract

► We have synthesized templated silica films to encapsulate non-wetting functionality in a hard matrix. ► Worn templated films retained non-wetting functionality after removal of the outer layers of the coating. ► The templating process weakened the film by increasing porosity, but the encapsulated non-wetting groups reduced friction and thus reduced wear. ► AFM topographic and friction force micrographs showed compositional distribution of film and the wear mechanism for abrasion by polishing. ► Tribological properties of the films can be tuned using the surfactant templating process. Functional mesoporous thin films have been used to encapsulate organic functionality within a ceramic matrix. Such coatings are broadly applicable to a range of applications including, anti-fouling coatings, controlled release, anti-microbial, and anti-corrosive films – all of which may involve interactions between an exposed solid surface and a mechanically abrasive environment. This area requires consideration of tribological performance, which has not yet been adequately studied. This study examines some of the key elements in the tribology of functional mesoporous thin films with the aim of facilitating the design of durable functional materials. Fluorinated mesoporous silica films were deposited by sol–gel synthesis on glass substrates. The resulting non-wetting and low-friction coating material was a thin film consisting of a hard silica matrix encapsulating fluoropolymer functionality within nanometer-scale pores. Structural, mechanical, surface, and tribological properties were investigated to examine the performance of these films in tribological environments. Analytical techniques used include nanoindentation, nanoscratch, AFM, contact angle goniometry, XPS, porosimetry, stylus profilometry, and a reciprocating polishing wear apparatus. Various compositions were synthesized to understand the effect of organic functionality on tribological performance. Coating properties were monitored during abrasion to elucidate the evolution of performance as the material is worn. The results of this investigation will contribute to the design of sacrificial coatings that provide sustained functionality during abrasive wear.