Tuning the Structure and Ionic Interactions in a Thermochemically Stable Hybrid Layered Titanate-Based Nanocomposite for High Temperature Solid Lubrication

Abstract

Solid inorganic lubricants are thermally stable but they are often limited by their lack of deformability, while organic lubricants have limitations in terms of thermal stability. In this study, a novel solid organic–inorganic nanocomposite lubricant that synergistically combines the thermochemically stable structure of a layered oxide with the relative softness of an organic polymer is presented. The nanocomposite is made by intercalating 11-aminoundecanoic acid in a lepidocrocite-type protonated titanate, H1.07Ti1.73O4. The amino acid molecules rapidly arrange to form a paraffinic bilayer in the gallery region of the layered host. This topotactic reaction yields a well-organized layered nanocomposite consisting of inorganic 2D titanate layers separated by amino acid molecules. Above elevated temperatures, 11-undecanoic acid polymerizes into nylon-11 confined between crystalline titanate monolayers. The lubricating properties of these nanocomposites up to 580 °C are determined using high-temperature pin-on-disc experiments using steel-steel contacts. The lubricative properties are based on the softening of the intercalated polymer above 200 °C. The encapsulation of the polymer chains by the inorganic titanate monolayers protects the organic component from thermal degradation and increases the thermal stability of the system.