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.

 

 

 

 

 

Colloidal crystals exhibit structural color without any color pigment due to the crystals’ periodic nanostructure, which can interfere with visible light. This crystal structure is iridescent as the resulting color changes with the viewing or illumination angle, which limits its use for printing or displays. To eliminate the iridescent property, it is important to make the packing of the colloidal nanoparticles disordered. Here, we introduce a drop-casting method where a droplet of a water- ethanol mixture containing monodisperse polymer-coated silica nanoparticles creates a relatively uniform and non-iridescent deposit after the droplet evaporates completely on a heated substrate. The uniformity is caused by a thermal Marangoni flow and fast evaporation effects due to the heated substrate, whereas non-iridescence is the outcome of short-range-ordered packing of nanoparticles by depletion attraction and friction effects produced by polymer brushes. We show that the colors of the final deposits from individual droplets remain unchanged while the viewing angle is varied under ambient light. We expect that the coating method is compatible with ink-jet printing and the uniformly coated self-assembled non-iridescent nanostructures have potential for color displays using reflection mode and other optical devices.

 

Related publication:

S. Y. Lee, H. Kim, S.-H. Kim, and H.A. Stone "Uniform coating of self-assembled noniridescent colloidal nanostructures using the Marangoni effect and polymers," PHYSICAL REVIEW APPLIED, accepted. [PDF(Impact factor: 4.782)

 

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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.