CAS: Rheo-tribology of Triglyceride-Derived Oligomeric Fluids and Associative Polymer Thickeners

NON-TECHNICAL SUMMARY: Lubricants like oil or grease reduce friction, extend machine life, and limit wasted energy in transportation, manufacturing, and power generation. Plant and animal oils offer alternatives to petroleum-based lubricants but can be more expensive and perform poorly at high temperatures or during long use. This project supports fundamental research aimed at converting residual fats into safer and affordable lubricants. Combining them with polymers will improve performance of lubricants that are exposed to stresses in machines during use. The central question is whether a set of measurable features can predict how these lubricants will perform to prevent surface damage to machines in which the lubricant is used. The research team will prepare fat-derived fluids and polymers, test them under conditions of moving machine parts, and identify formulations that protect metal surfaces. This project serves the national interest by advancing materials science relevant to U.S. advanced manufacturing, transportation, and energy infrastructure. Student researchers will receive broad training in a variety of technical fields to advance the future workforce. Project data, analysis tools, publications, and educational materials will be shared broadly to strengthen the U.S. science and engineering enterprise. TECHNICAL SUMMARY: This project establishes structure-property relationships for polar, residual-lipid-derived lubricant base fluids with associative polymer thickeners. The central hypothesis is that friction and wear can be predicted from two coupled descriptors: bulk transient-network relaxation and recovery, and selective adsorption and retention of polymer association groups at steel and oxide interfaces. Aim 1 constructs model lipid mixtures varying free fatty acid content, glyceride distribution, unsaturation, water, amphiphiles, and oxidation-related functionality. These mixtures and real residual lipid feeds are converted into polyol esters, estolide-type oligomers, and branched or dimer-acid esters with controlled molecular weight, branching, and polarity. Telechelic and comb methacrylate polymers contain aromatic or urea-based association groups at controlled densities and spacings. Spectroscopic, chromatographic, calorimetric, and thermal analyses characterize the materials. Steady shear, viscosity-temperature, oscillatory shear, thixotropic recovery, stress growth, and creep measurements generate a composition-structure-rheology map and guide selection formulations. Aim 2 uses ball-on-disk and four-ball tribology, Stribeck mapping, start-stop friction protocols, pressure- and temperature-dependent viscosity measurements, profilometry, and microscopy on relevant surfaces. The measurements test whether lubrication-regime transitions, friction transients, wear, and boundary-film retention scale with the ratio of bulk relaxation time to contact deformation time and with interfacial selectivity. The project releases a dataset and analysis profiles, pursues open-access publication when feasible, and trains students in polymer synthesis, rheology, tribology, surface characterization, and reproducible data analysis. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.