Measuring temperature gradients in evaporating multicomponent alcohol/water droplets

We demonstrate that temperature gradients can be investigated in evaporating volatile water/ alcohol droplets by characterising the volume averaged temperature by laser induced fluorescence and the near-surface temperature by cavity enhanced Raman scattering. In the former technique, the fluorescence spectrum from Rhodamine B can be used to determine the droplet temperature with an accuracy of +/- 1 K. The latter technique uses the band width of the OH stretching Raman band to determine the temperature change within the near-surface volume in which whispering gallery modes propagate with an accuracy of +/- 4 K. We demonstrate that the temperatures measured with varying evaporation time, buffer gas pressure, droplet size and composition are consistent with the predictions from a quasi-steady theoretical treatment of the evaporation rate and can be used to investigate temperature gradients within evaporating droplets.