Thermal Characterization of Liquid Analytes via Photothermal Modulation of Microfluidic Resonators

This paper reports the first thermal characterization of liquid analytes via photothermal modulation of microfluidic resonators in dynamic mode. Measurements of thermophysical properties of liquid analytes are enabled by real-time tracking of the resonance frequency shift of the microfluidic resonator while the liquid filled resonator is irradiated by a diode laser. The local irradiation induces the photothermal heating of the resonator as well as the loaded liquid sample. The volumetric thermal expansion coefficients of various liquids are correlated with resonance frequency shifts of the resonator and the ratio of specific heat to thermal conductivity tuned by varying the mole fraction of ethanol-water binary mixtures shows linear dependence on the heating time constant. In addition, a higher flexural mode displays improved sensitivity for thermal characterization of liquids via photothermal heating.