High density deposits of binary colloids.

Colloids are essential materials for modern inkjet printing and coating technology. For printing and coating, it is desirable to have a high density of colloids with uniformity. Binary colloids, which consist of different size colloidal particles, have the potential to achieve high coating density and uniformity from size effects. We report a strategy to attain high-density deposits of binary colloids with uniform, crack-free, and symmetric deposits through droplet evaporation on micropillar arrays. We modify surfaces of micropillar arrays with plasma treatment to control their surface energy and investigate how binary colloidal fluids turn into well-controlled deposits during evaporation with X-ray microscopic and tomographic characterizations. We attribute temporary surface energy modification of micropillar arrays to the well-controlled high-density final deposits. This simple, low-cost, and scalable strategy would provide a viable way to get high-quality, high-density deposits of colloids for various applications.