NONCONTACT FLUORESCENCE THERMOMETRY OF ACOUSTICALLY LEVITATED WATERDROPS

Noncontact thermometry based on the fluorescence excitation spectrum of aqueous Eu3+(EDTA) near 579 nm allows us to measure the temperature of an evaporating drop of water. The results for drop diameters in the 500-Mm-3-mm range confirm theoretical temperature predictions for steady state evaporation. Calibration of the excitation spectrum in a constant temperature cell indicates that ±1.0°C resolution is possible for temperatures below 20° C. The spectrum depends only on the solution temperature when Eu3+(EDTA) concentrations are below IX 10-3 M and when the solution pH is between 4.0 and 10.0. Excitation spectra from levitated waterdrops contain additional noise which degrades the temperature resolution to ±1.2°C. With this technique we are able to follow the temperature change in an evaporating drop of water as a monolayer of 1-octadecanol forms on the surface and retards the evaporation. © 1990 Optical Society of America.