Controlling the wetting and evaporation dynamics of non-ideal volatile binary solutions

Volatile binary liquid samples on wetting substrates are known to undergo either spreading or contraction tendencies, as a result of solutal Marangoni stresses due differential volatility. Enhanced is commonly thought occur when the lower surface tension component more ‘volatile’, while expected otherwise. We seek test limits this scenario for various configurations such sessile drops with free pinned contact lines, without microparticles, and tears-of-wine menisci. consider isopropanol- ethanol–water mixtures, important in numerous applications. conduct interferometric experiments droplets multiple combinations initial concentration controlled ambient humidity (water vapour only), essentially covering entire range these parameters. Experiments also carried out other mentioned above. Contraction regimes found certain situations where expected, despite alcohols being volatile than water. Furthermore, regime reversals between cases different concentrations even at zero humidity, not necessarily associated existence an azeotropic composition. Such surprising observations rationalized by simple model highlighting often overlooked role diffusion coefficient ratio two vapours conjunction non-ideality mixture. Our picture phenomenon demonstrated be universal all studied.