Abstract
The present study aims to measure the solid–liquid interface temperature of an evaporating droplet on a heated surface using a thermoresponsive polymer. Poly(N-isopropylacrylamide) (pNIPAM) was used owing to its sensitive optical and mechanical properties to the temperature. We also measured the refractive index variation of the pNIPAM solution by using the surface plasmon resonance imaging (SPRi). In particular, the present study proposed a new method to measure the solid–liquid interface temperature using the correlation among reflectance, refractive index, and temperature. It was found that the reflectance of a pNIPAM solution decreased after the droplet deposition. The solid–liquid interface temperature, estimated from the reflectance, showed a lower value at the center of the droplet, and it gradually increased along the radial direction. The lowest temperature at the contact line region is present because of the maximum evaporative cooling. Moreover, the solid–liquid interface temperature deviation increased with the surface temperature, which means solid–liquid interface temperature should be considered at high temperature to predict the evaporation flux of the droplet accurately.
Highlights
Droplet evaporation is a ubiquitous phenomenon in nature, and it has the advantage of transferring larger thermal energy than usual convective-cooling techniques
The present study proposed a novel method to measure the temperature using the pNIPAM solution and surface plasmon resonance imaging (SPRi) technique, and the solid–liquid interface temperature of the droplet was predicted by calculating the heat conduction problem with the measured
The present study proposed a novel method to measure the temperature using the pNIPAM solution and SPRi technique, and the solid–liquid interface temperature of the droplet was predicted by calculating the heat conduction problem with the measured temperature using pNIPAM solution
Summary
Droplet evaporation is a ubiquitous phenomenon in nature, and it has the advantage of transferring larger thermal energy than usual convective-cooling techniques. The reflected light from the metal surface has the lowest intensity at the SPR angle, which changes only by the refractive index of the test medium with a fixed configuration of the prism, gold film thickness, and wavelength.
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