Simultaneously Suppressing the Coffee Ring Effect of Solutes with Different Sizes

Suppressing the coffee ring effect (CRE), which improves the uniformity of deposition, has attracted great attention. Usually, a realistic system contains solutes of various sizes. Large particles preferentially settle onto the substrate under gravity, separated from small particles even when CRE is suppressed, which generates nonuniformity in another way. This hinders small particles from filling the gaps at the deposition-substrate interface, leaving a frail deposition. Here, the CRE of polydispersed solutes is simultaneously suppressed, and a more uniform deposition is achieved by suspending the drop together with adding trace amounts of cations. The gaps tend to be filled, which makes the deposition bind more tightly. Analysis shows that gravity coordinates with the interactions that mediate the attraction between particles and the substrate, resulting in the coinstantaneous adsorption of all particles. This work adds another dimension to the suppression of CRE, improving the uniformity of deposition in complex systems and paving the way for the development of techniques in diverse manufacturing industries.