Concurrent determination of heat and capacity change of a sessile droplet using a single measurement

Microcalorimetry, designed for the independent measurement of enthalpy and heat capacity, has been commercially available for a considerable time. However, heat-related states in samples, especially liquids, can introduce complicated phenomena and challenging measurement and data evaluation processes. Such complexity becomes apparent when observing fluctuations in heat capacity (C_p) while measuring heat consumption (Q) during water evaporation. This paper presents a continuous heat pulse measurement (CHPM) method for concurrently analyzing Q and C_p in a single test using microcalorimetry. The sample droplet of 400 nL was directly dispensed on the microcalorimeter surface, followed by a light-emitting diode (LED) radiation generating heat to perform CHPM. We repetitively heated the microcalorimeter using heat pulses provided by LED irradiation, with their duration set to 100 ms and 10 s repetition, while measuring the temperature response of the microcalorimeter. A MATLAB-based simulation model was established to validate the accuracy of our C_p measurements, which show its value of 0.79 % of minimum variance. Water evaporation coupled with simultaneous salt crystallization served as our study model, where the C_p values were calculated from real-time responses to heat pulses provided by LED. The experimental outcomes confirm the suitability of CHPM in extracting key thermal properties and emphasize its versatility as a diagnostic tool, providing a significant method for research and applications in the fields of physics, engineering, and beyond.