Materials Science

Exploiting Evaporation

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Science  04 Dec 2009:
Vol. 326, Issue 5958, pp. 1323
DOI: 10.1126/science.326.5958.1323-d

There are many approaches available to pattern soft materials such as colloidal films, but they often require multiple processing steps and allow deposition of only a few particle layers. A method called evaporative lithography overcomes these limitations, and Harris et al. now show that the method also enables the creation of patterns from binary mixtures of particles. Evaporative lithography exploits the fact that when aqueous and organic droplets dry, particles within the droplets are deposited in different patterns. Aqueous droplet evaporation leads to the familiar coffee-ring effect, whereas when nonaqueous droplets evaporate, most particles are deposited at the center. Use of a mask modulates the evaporative landscape of a drying droplet or film, resulting in pattern formation. The authors demonstrate generation of diverse patterns by tuning the mask design, mixture composition, and particle size ratio for an aqueous mixture of silica microspheres and sulphonated polystyrene nanoparticles. The method is simple and versatile and may be used to pattern colloidal, polymeric, and biomolecular species.

Philos. Trans. R. Soc. London Ser. A 367, 5157 (2009).

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