Micro-Raman investigations on the structures of the surface and the inner of MgSO4 droplets

Spherical MgSO₄ droplets were deposited by a syringe on the hydrophobic Teflon substrate. Using micro-Raman technique, the laser beam was highly focused twice on the surface and in the center of spherical droplets. The Raman spectra for the surface and the inner of MgSO₄ droplets were accordingly obtained, suggesting formation of a thin layer of gels on MgSO₄ droplets at low relative humidity. The gel layer covered the surface and exhibited a significant delay in response to the change of ambient relative humidity, resulting in the structural difference between the surface and the inner of MgSO₄ droplets. Supported by the National Natural Science Foundation of China (Grant Nos. 20673010 and 20640420450), the “111” Project (Grant No. B07012), and the Incubation and Reward Foundation for Excellent Doctoral Dissertation of Beijing Institute of Technology