Thermal conductivity of methanol-ethanol mixture and silicone oil at high pressures

Abstract

4:1 methanol-ethanol (ME) mixture and silicone oil are common, important pressure transmitting media used in high pressure diamond anvil cell (DAC) experiments. Their thermal conductivities and elastic properties are critical for modeling heat conduction in the DAC experiments and for determining thermal conductivity of measurement samples under extreme conditions. We used time-domain thermoreflectance and picosecond interferometry combined with the DAC to study the thermal conductivities and elastic constants C11 of the ME mixture and silicone oil at room temperature and to pressures as high as ≈23 GPa. We found that pressure dependence of the thermal conductivity of ME and silicone oil are both well described by the prediction of the minimum thermal conductivity model, confirming the diffusion of thermal energy between nonpropagating molecular vibrational modes is the dominant heat transport mechanism in a liquid and amorphous polymer. Our results not only provide new insights into the physics of thermal transport in these common pressure media for high pressure thermal measurements, but will also significantly extend the feasibility of using silicone fluid medium to much higher pressure and moderately high temperature conditions with higher measurement accuracy than other pressure media.