The molecular structures, rheological properties, and friction coefficients of several new siloxane-based polymers were studied to explore their traction characteristics. The molecular structures including branch content were established by nuclear magnetic resonance spectroscopy, while the molecular mass distributions were determined by gel permeation chromatography. Density, viscosity, elastohydrodynamic film formation, and friction were investigated over a temperature range of 303–398 K. Film thickness and friction measurements were studied under the conditions that are representative of boundary, mixed, and full-film lubrication regimes, aiming at maximizing traction performance and temperature stability by simultaneous optimization of the size and content of ring-shaped branch structures. This study provides quantitative insight into the effect of siloxane molecular structure on the tribological performance for traction drive applications such as continuously variable transmissions.
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Appendix: Synthesis and Experimental Procedures
Appendix: Synthesis and Experimental Procedures
Synthesis of PCMS
The procedure for the synthesis of PCMS 50 was also representative for the synthesis of PCMS 90. All chemical reactions were carried out in oven-dried flasks under N2 unless otherwise noted. All reagents and catalysts were obtained from commercial vendors and used as received. A 100 mL Parr Micro Reactor equipped with a Teflon reaction vessel, a pressure gauge, an H2 inlet, and a mechanical stirrer was used, and heating was charged with poly(phenylmethylsiloxane) PPMS 50 (10 mL) and 10 % Palladium on Charcoal (1 g). After sealing and purging the reaction vessel with H2, the reactor was heated to 413 K with vigorous stirring and 4.14 MPa H2 (Fig. 2). During the course of the reaction, the H2 pressure was renewed when it fell below 3.45 MPa. The reaction was kept stirring until the pressure became constant. The reactor was then cooled to room temperature and the pressure released to the atmosphere. After carefully opening the reactor, the black residue was dissolved with hexanes, filtered through Celite, and the solvent was removed in vacuo. The obtained clear oil was dried under high vacuum overnight to provide pure product.
NMR Experimental Details
1H NMR spectra were recorded on Varian Inova (500 MHz) spectrometers. Chemical shift values (δ) were expressed in ppm using signal of solvent residue as the internal standard (CHCl3 at 7.26 ppm). 13C NMR spectra were recorded on Varian Inova (125 MHz) spectrometers and were expressed in ppm using solvent as the internal standard (CDCl3 at 77.16 ppm). The results are as follows.
PCMS 50. 1H NMR (CDCl3): δ 1.74 (m), 1.20 (m), 0.55 (m), 0.09 (m), 0.08 (m) 0.05 (m), 0.01 (m), −0.02 (m). 13C NMR (CDCl3): δ 28.03, 28.01, 27.99, 27.96, 27.87, 27.70, 27.63, 27.59, 27.57, 27.49, 27.12, 26.81, 26.76, 26.71, 26.67, 26.65, 2.09, 2.05, 1.97, 1.95, 1.52, 1.46, 1.38, 1.33, 1.30, 1.24, −2.14, −2.19, −2.24, −2.32.
PCMS 90. 1H NMR (CDCl3): δ 1.72 (m), 1.20 (m), 0.56 (m), 0.09 (m), 0.10 (m) 0.03 (m), −0.01 (m), −0.02 (m). 13C NMR (CDCl3): δ 28.03, 28.02, 27.99, 27.95, 27.90, 27.74, 27.72, 27.69, 27.60, 27.18, 27.16, 27.14, 26.88, 26.83, 26.81, 26.68, 2.10, −1.93, −2.02, −2.10, −2.36.
GPC Experimental Details
The chromatographic equipment consisted of a Waters 2695 Separations Module equipped with a vacuum degasser, and a Waters 2410 differential refractometer. The separation was made with two (300 × 7.5 mm) Polymer Laboratories PLgel 5 μm Mixed-C columns (molecular weight separation range of 200–2,000,000), preceded by a PLgel 5 μm guard column (50 × 7.5 mm). The analyses were performed using certified grade THF flowing at 1.0 mL/min as the eluent, and the columns and detector were both heated to 35 °C. The samples were prepared in THF at about 0.5 % w/v solids, solvated about 2 h with occasional shaking, and transferred to autosampler vials without filtering. An injection volume of 100 μL was used and data were collected for 25 min. Data collection and analyses were performed using ThermoLab Systems Atlas chromatography software and Polymer Laboratories Cirrus GPC software. Molecular weight averages were determined relative to a calibration curve (3rd order) created using the polystyrene standards covering the molecular weight range of 580–2,300,000.
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Zolper, T., Li, Z., Jungk, M. et al. Traction Characteristics of Siloxanes with Aryl and Cyclohexyl Branches. Tribol Lett 49, 301–311 (2013). https://doi.org/10.1007/s11249-012-0066-x
- Synthetic base stocks
- EHL friction (traction)
- Continuously variable transmissions (CVT)
- Traction fluids