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... full DRO policy for further details. ABSTRACT: The evaporation of colloidal drop on a substrate with a pinned contact line usually results in a ring stain (the so-called coffee-ring effect). In this paper, we present an investigation of the evaporation of sessile picoliter droplets of binary solvent mixtures containing fumed silica nanoparticles (NPs). The internal flows in ethanol/water droplets are suppressed and uniform deposit morphology achieved with a low loading (0.2-0.5 vol.%) of hydrophobic fumed silica NPs. The effective control of the particle deposit morphology is based on a rapid solgel transition assisted by preferential evaporation of ethanol. For droplets of dilute suspensions, the fumed silica NPs tend to agglomerate (AVI) -the drying process for a 30 vol.% ethanol/water droplet with 0.2 vol.% hydrophobic fumed silica PSs and 0.01 vol.% PS tracer particles; playback rate 0.05xReal time. Movie S5 (AVI) -the drying process for a 30 vol.% ethanol/water droplet with 0.005 vol.% PS tracer particles; playback rate 0.05xReal time. Movie S6 (AVI) -the drying process for a 30 vol.% ethanol/water droplet with 0.5 vol.% hydrophobic fumed silica PSs and 0.01 vol.% PS tracer particles; playback rate 0.05xReal time. AUTHOR INFORMATION