In order to validate our ideas, formamide (FA), a solvent with a higher boiling point (210 °C) and a lower surface tension (59.09 mN/m) than water, was selected to become the co-solvent in P(St-MAA) colloidal inks. As shown in Figs. 7 and 8, it was found that the higher the amount of FA, the smaller the coffee ring becomes. In particular, the “coffee ring” effect on fabric substrates can be well suppressed with 4–6 vol% FA in ink. After mixing water and FA together as a solvent system, the evaporation time of the deposited droplets becomes longer, and water preferentially evaporates more at the edge than FA. Consequently, the concentrations of FA at the edge region become higher, which reduces the surface ten- sion of the related region, and the resulting surface tension gradient induces inward capillary flow from the edge to the center, which counteracts the outward capillary flow to form uniform deposited droplets without the coffee ring effect.