Drying, Coating & Printing
We study how colloids pack each other and leave a specific pattern, which can be changed by the surface condition of colloids and working fluid. We focus on optimizing the coating solution system to obtain a uniform pattern. Additionally, we endeavor to develop a novel control coating method, in particular ordered versus disordered packing structures. Our coating method can be applied to the organic or inorganic materials coating or printing technologies. Furthermore, to combine our developed model and 2D or 3D printing technologies, we will construct a printing system for mass production manufacturing.
A single monolayer coating of colloidal particles is extensively studied over last several decades. However, to stack multiple layers of particles with a uniform thickness is still lacking and the fabrication process can be typically complex. Here, we study how condensed colloidal particles uniformly coat on a substance with a single-step coating method. We expect this coating method can be used for ink-jet printing and 3D-printing technologies. We are also interested in manipulating packing shape of the colloidal structure using physico-chemical effects. The detail research results would be described in the near future.
Ellipsoidal particles have previously been shown to suppress the coffee-ring effect in millimeter-sized colloidal droplets. Compared to their spherical counterparts, ellipsoidal particles experience stronger adsorption energy to the drop surface where the anisotropy-induced deformation of the liquid−air interface leads to much greater capillary attractions between particles. Using inkjet-printed colloidal drops of varying drop size, particle concentration, and particle aspect ratio, the present work demonstrates how the suppression of the coffee ring is not only a function of particle anisotropy but rather a competition between the propensity for particles to assemble at the drop surface via capillary interactions and the evaporation-driven particle motion to the contact line. For ellipsoidal particles on the drop surface, the capillary force (Fγ) increases with the particle concentration and aspect ratio, and the hydrodynamic force (Fμ) increases with the particle aspect ratio but decreases with drop size. When Fγ/Fμ > 1, the surface ellipsoids form a coherent network inhibiting their migration to the drop contact line, and the coffee-ring effect is suppressed, whereas when Fγ/Fμ < 1, the ellipsoids move to the contact line, resulting in coffee-ring deposition.
D.-O. Kim, M. Pack, H. Hu, H. Kim, and Y. Sun, “Deposition of Colloidal Drops Containing Ellipsoidal Particles: Competition between Capillary and Hydrodynamic Forces,” Langmuir 32(45), 11899 (2016)