All surface resistance measurements were performed with a 2400 Sourcemeter (Co. Keithley Instruments) with a 4-wire sense mode configuration in combination with a custom made 4-point measuring probe. The cylindrical probe tips were arranged in line with a diameter of 0.8 mm and a distance between the probes of 2.1 mm. A constant current was applied through the outer probe tips to the sample. The voltage drop from the outer to the inner probe tips was used for resistance calculation based on a method described by Schroder et al.56 Each measurement was performed with a constant current in the range of 1 μA to 1 mA at 2.1 V for 200 s of measurement time. The average value of 6 measurements at different locations on the sample surface is reported for each of the samples.
Attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR) was recorded with a 1.9 cm−1 spectral resolution on a 670 FT-IR spectrometer (Co. Varian Inc. (now: Agilent Technologies)). The assignment of measured vibrations were supported by DFT-based calculations on a D3(BJ)-BP86-def2-SVP level of theory.57–61 Deviations to the measured spectra were described by Benavides-Garcia and Monroe.62 All calculations were carried out using the ORCA computational chemistry program.63,64 Raman spectra were recorded on an inVia confocal (Co. Renishaw) with an excitation wavelength of 532 nm, 3 times for each specimen with 20 s exposure time. Hardness testing was performed using a Fischerscope H100C XYp Nanoindenter (Co. Helmut Fischer GmbH) using a Vickers diamond indenter. After contact with the surface, the indenter was approached into specimens at a constant rate of 300.00 mN/60 s until 150 mN of force was reached and withdrawn from the surface at the same rate as loading. At least 12 indentations were performed for each specimen and the average value was reported. Surface roughness measurements and optical imaging were performed using a VK-9700 Color 3D-Laser scanning microscope (Co. Keyence Corporation). For each sample, at least five randomly selected areas of the surface were measured and the surface roughness Ra and surface depth Rz were determined. High-resolution images of the composite material were taken using a scanning electron microscope (SEM, S-3400N, Co. Hitatchi Science Systems, Ltd) and spectral maps for sulfur and phosphorus were prepared using energy dispersive X-ray spectroscopy (EDX). The samples were fractured after storage in liquid nitrogen for at least 3 h and the exposed surface was coated with a thin platinum layer using a high vacuum platinum sputter at low voltage (brittle fractures). High-resolution transmission electron microscopy (FEI, Talos 120C, Co. Thermo Fisher Scientifics) images were taken of selected polymer compounds. Therefore, very thin lamellae were sectioned with a diatome diamond knife (Cryo-Mikrotomy, Co. Reichert-Jung Ultracut E and RMC CR-X Cryoattachment) at a temperature of −120 °C. The freshly microtomed sample surfaces were subsequently measured by AFM (MultiMode 8, Co. Brucker). The ultrathin sections (about 60 nm) were collected and used for TEM measurements. By evaluating the distribution of the added liquid and solid lubricants in the bulk material, the tribological mechanisms leading to self-lubrication will be analyzed.
Attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR) was recorded with a 1.9 cm−1 spectral resolution on a 670 FT-IR spectrometer (Co. Varian Inc. (now: Agilent Technologies)). The assignment of measured vibrations were supported by DFT-based calculations on a D3(BJ)-BP86-def2-SVP level of theory.57–61 Deviations to the measured spectra were described by Benavides-Garcia and Monroe.62 All calculations were carried out using the ORCA computational chemistry program.63,64 Raman spectra were recorded on an inVia confocal (Co. Renishaw) with an excitation wavelength of 532 nm, 3 times for each specimen with 20 s exposure time. Hardness testing was performed using a Fischerscope H100C XYp Nanoindenter (Co. Helmut Fischer GmbH) using a Vickers diamond indenter. After contact with the surface, the indenter was approached into specimens at a constant rate of 300.00 mN/60 s until 150 mN of force was reached and withdrawn from the surface at the same rate as loading. At least 12 indentations were performed for each specimen and the average value was reported. Surface roughness measurements and optical imaging were performed using a VK-9700 Color 3D-Laser scanning microscope (Co. Keyence Corporation). For each sample, at least five randomly selected areas of the surface were measured and the surface roughness Ra and surface depth Rz were determined. High-resolution images of the composite material were taken using a scanning electron microscope (SEM, S-3400N, Co. Hitatchi Science Systems, Ltd) and spectral maps for sulfur and phosphorus were prepared using energy dispersive X-ray spectroscopy (EDX). The samples were fractured after storage in liquid nitrogen for at least 3 h and the exposed surface was coated with a thin platinum layer using a high vacuum platinum sputter at low voltage (brittle fractures). High-resolution transmission electron microscopy (FEI, Talos 120C, Co. Thermo Fisher Scientifics) images were taken of selected polymer compounds. Therefore, very thin lamellae were sectioned with a diatome diamond knife (Cryo-Mikrotomy, Co. Reichert-Jung Ultracut E and RMC CR-X Cryoattachment) at a temperature of −120 °C. The freshly microtomed sample surfaces were subsequently measured by AFM (MultiMode 8, Co. Brucker). The ultrathin sections (about 60 nm) were collected and used for TEM measurements. By evaluating the distribution of the added liquid and solid lubricants in the bulk material, the tribological mechanisms leading to self-lubrication will be analyzed.
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