Silicon sensor for microdroplets of volatile liquids

The possibility of identifying liquid substances by their evaporation efficiency from a silicon substrate is investigated. Two sensor designs were used as test models. The first is a silicon rod with thermally insulated side walls, loaded with liquid from one of the ends and probed by a volumetric acoustic wave. The second sensor is a silicon wafer loaded with liquid on one side and probed by a surface acoustic wave propagating from the opposite side of the wafer. It is shown that in both structures, due to the high thermal conductivity of silicon, the temperature changes of the evaporating substance are transmitted almost unchanged to the probing waves, changing their speed. It is established that during the main stage of evaporation, the temperature of the droplet practically does not change, and at the last stage it experiences quasi-periodic temperature variations, accompanied by droplet breaks into individual islands and their rapid disappearance. The temperature and evaporation rate of ethyl alcohol, isopropyl alcohol, acetone, and n-hexane droplets with a volume of about 10 µl were measured.