Measurement of composition of mixtures at high pressures is important in many applications such as supercritical drying of aerogels, high-pressure sterilization and synthesis of nanostructured materials. The frequency response of uncoated microcantilevers immersed in ethanol-CO2 mixtures with compositions ranging from 0.85 to 4 weight % of ethanol in ethanol-CO2 were measured at a temperature of 318 K and pressure range of 10 MPa to 22 MPa. The resonant frequencies and Q-factors were found to decrease with the increasing weight % of ethanol in the mixture. The data indicate that the composition of a mixture can be measured by measuring the resonant frequency of the cantilever in the mixture after obtaining a calibration curve by measuring resonant frequencies of mixtures with known composition. The sensitivity of the technique which is defined as the ratio of resonant frequency shift to the change in fluid mixture was investigated. An analytical expression for sensitivity was derived using Sader’s model. The sensitivity was found to be a complex function of density and viscosity of the mixture as well as the length, density and width of the cantilever. Using the density and viscosity data in the literature for ethanol-CO2 mixtures with various compositions, the sensitivity of the cantilevers were calculated at each pressure and temperature. The results indicate that the minimum composition that can be measured with the current setup is between 480 ppm and 980 in the pressure range of 10 MPa to 22 MPa by using a 150 µm long cantilever and between 600 and 1450 ppm by using 200 µm long cantilever. Acknowledgment: - This project has received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 685648.

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Shadi Khan Baloch, Alper Kiraz, Alexandr Jonáš, B. Erdem Alaca, and Can Erkey, "Measurement of composition of mixtures at high pressures with high sensitivity using frequency response of microcantilevers (Conference Presentation)," Proc. SPIE 10491, Microfluidics, BioMEMS, and Medical Microsystems XVI, 104910T (Presented at SPIE BiOS: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287850.5751463091001.