Structural, mechanical, and tribological properties of fluorinated mesoporous silica films: Effect of functional moiety and surfactant template concentrations

Thin organo-functional coatings are inherently weak and can be easily damaged and their functional properties degraded by wear. Encapsulating organo-functional moieties into surfactant-templated ceramic coatings has the possibility of extending the functional lifetime of such materials. This study examines the effects of functional silane and surfactant template concentrations on the structural, mechanical, and tribological properties of hydrophobic silica films. Fluorinated silica films were synthesized via sol–gel co-condensation of tetraethoxysilane and a perfluoropolyether silane, templated with PEO106PPO70PEO106 surfactant (Pluronic F127), and coated on glass substrates. The results show that the increasing concentrations of fluorinated silane and surfactant template generally improve hydrophobicity of films worn by abrasion. However, surfactant templating creates void spaces which are detrimental to the mechanical properties of the material, as was determined by nitrogen adsorption porosimetry and nanoindentation. Tribological results from atomic force microscopy suggest that the low-friction surface generated by encapsulation of fluorosilane moieties grafted to internal surfaces mitigates to some extent the detrimental effect of film porosity on hardness and wear resistance.

► Surfactant templating of silica films aided in bulk encapsulation of fluorosilanes.
► Encapsulation increased hydrophobicity of film bulk after removal of top surface.
► Porosity increased with encapsulation, leading to softer films.
► Wear rate varied with composition in three different mechanisms.
► Hardness, lubricity, and adhesion were all found to influence wear rate.