Bifurcation and Transposition of the Wicking Front of Binary Solutions Infiltrating into Chromatography Paper Associated with Their Evaporation.

Nonequilibrium fluid patterns, such as Marangoni contraction, coffee rings, and tears of wine, are generated in binary solutions spread on a substrate during their evaporation. In this study, we observed another type of nonequilibrium behavior exhibited by binary solutions as they infiltrate porous materials and undergo evaporation. A binary solution comprising hexane and ethanol was brought into contact with the chromatography paper to facilitate infiltration into the paper's pores. Because the experimental setup was in an open environment, infiltration and evaporation occurred simultaneously. The wicking front exhibited an initial rapid advancement, followed by subsequent receding and readvancing. Additionally, the bifurcation of the wicking front after the onset of its readvancement was confirmed by monitoring the temporal evolution of the spatial luminance distribution and temperature distribution on the surface of the chromatography paper. Chromatographic development of a hydrophilic dye was conducted in this experimental setup in an open environment. Additionally, it was confirmed that the receding and readvancing of the wicking front represented the transposition of the bifurcated wicking fronts.