  Surfactants have been widely studied and used in controlling droplet
evaporation. In this work, we observe and study the crystallization of sodium
dodecyl sulfate (SDS) within an evaporating glycerol-water mixture droplet. The
crystallization is induced by the preferential evaporation of water, which
decreases the solubility of SDS in the mixture. As a consequence, the crystals
shield the droplet surface and cease the evaporation. The universality of the
evaporation characteristics for a range of droplet sizes is revealed by
applying a diffusion model, extended by Raoult's law. To describe the
nucleation and growth of the crystals, we employ the 2-dimensional
crystallization model of Weinberg [J. Non-Cryst. Solids 1991, 134, 116]. The
results of this model compare favorably to our experimental results. Our
findings may inspire the community to reconsider the role of high concentration
of surfactants in a multicomponent evaporation system.
