Partition coefficients for a mixture of two lubricant oligomers

Abstract

Universal base oils that remain pourable over wide temperature ranges would have important advantages for lubrication applications. The model system used in this project was a poly(a-olefin) synthetic base oil modified with polydimethylsiloxane (PDMS) to lower the pour-point temperature. Although the blend was miscible at room temperature, phase separation occurred at temperatures lower than 258 K. Partition coefficients of such nonideal oligomer mixtures can (1) help define operating temperature ranges and (2) provide a basis for designing molecular weight distributions of each lubricant that control or prevent phase separation. The poly(a-olefin) base oil family is branched oligomers with two to five n-mers at levels greater than 1 wt %, whereas PDMS additives are linear oligomers having between 10 and 50 sequential n-mers at levels greater than 0.5 wt %. In this study, Fourier transform infrared measurements of the poly(a-olefin) and PDMS compositions in each phase provided an overall material balance. Poly(a-olefin) oligomers were detected with size exclusion chromatography with a differential refractive-index detector, and PDMS oligomers were detected with matrix-assisted laser desorption/ionizationtime-of-flight mass spectrometry. The best sets of measurements for the individual oligomers in each phase were selected by minimization of the overall material balance errors. For both oligomers, components with high molecular weights were preferentially excluded from the phase rich in the other polymer and were relatively independent of temperature. The partition coefficients of poly(a-olefin) components increased with increasing oligomer length, whereas the partition coefficients of the PDMS components decreased with increasing oligomer length.

High-cycle electromechanical aging of dielectric elastomer actuators with carbon-based electrodes

“…The affinity between the polyalphaolefin oil of the carbon grease and the PDMS of the membrane is supported by two facts. First, polyalphaolefins oils and silicone oils are miscible at room temperature [29]. Second, hydrocarbons like heptane (chemically close to polyalphaolefins), swell PDMS to a high degree [30].…”

Graphite functionalization for dispersion in a two‐phase lubricant oligomer mixture

“…Phase separation occurs at temperatures less than -15 C. A detailed analysis on the partitioning of this oligomer mixture is reported elsewhere. 11 Oligomer blends of two chemically different materials provide an interesting option for varying lubricant properties for a variety of applications. A critical challenge for such mixtures is controlling their emulsion stability and achieving multiple properties at the same time, thermal conductivity and viscosity in this case.…”

“…Phase separation occurs at temperatures less than ‐15°C. A detailed analysis on the partitioning of this oligomer mixture is reported elsewhere 11. Oligomer blends of two chemically different materials provide an interesting option for varying lubricant properties for a variety of applications.…”