Substrate thinning decelerates droplet evaporation

Droplet evaporation on thin substrates is crucial in basic and applied physics, especially for emerging technologies using thin films and inkjet printing in flexible electronics. We experimentally investigate how substrate thickness influences droplet evaporation across different materials. Using fast X-ray microtomography, we visualize droplet dynamics on thin polymer membranes and find that substrate deformation has negligible effects. Instead, evaporation slows as substrate thickness decreases, indicating that heat transfer plays a dominant role. Infrared thermal imaging shows that temperature differences across substrates increase logarithmically with thickness, confirming reduced heat transfer in thinner substrates. Our results show that increasing the polymer substrate thickness from 1 to 8 mm enhances the heat transfer rate by 7.4 times, resulting in a 1.3 times increase in the evaporation rate constant. These findings highlight the practical significance of substrate thinning in linking droplet evaporation and heat transfer, which is critical for thin-film applications.