Fast determination of evaporation enthalpies of solvents and binary mixtures using a microsilicon chip device with integrated thin film transducers

A silicon chip device with two types of integrated platinum thin film resistors was applied for microcaloric measurements. It was shown that the device is capable of fast characterization of liquid evaporation behaviour and allows the determination of evaporation enthalpies for pure liquids and mixtures. The applicability was demonstrated for a wide range of solvents from nonpolar aliphatic solvents over polar organics to protic solvents (e.g. iso-octane, toluene, acetone, ethanol, methanol and water). The sample volumes were in the range of about 2-5 μL. The determination of transient times, in case of constant power mode, or the power integral over time was used for the fast estimation of binary liquid mixtures. Thermo-resistive measurements of 5 μL droplets of solvent mixtures like methanol/iso-propanol, ethanol/water, iso-octane/iso-propanol and iso-octane/1,4-dioxane showed significant changes in temperature characteristics and evaporation enthalpies in dependence on composition. The applied heating power was about 1 W, which corresponds to measurement times between a few seconds and a minute.