Evaporation‐driven octagonal particle deposition on the patterned substrate

Abstract

Understanding noncircular deposition patterns can offer broad applications; however, the phenomena have not been thoroughly studied. We experimentally investigate particle self-assembly of microspherical polystyrene particle-laden sessile droplets dried on a micropyramid cavity substrate. The particle sizes and concentrations in the droplets are found to modify the inner particle deposition with the octagonal perimeter. The droplets with mass concentrations of 0.5% and higher evaporate with the pinned contact lines. The capillary flow flushes the 3 µm particles to the contact line and creates octagonal outer-ring patterns. The 10 µm particles are more evenly distributed in the depositions of the dried droplets. However, at a high mass concentration of 2.6%, the particles adsorbed at the droplet liquid-air interface form an agglomerate and deposit toward the centerline, leading to the crater-shaped pattern. Higher concentrations provoke the thicker octagonal outer-ring depositions regardless of the particle sizes in the droplets. The findings could inspire applications to control noncircular wetting and drying of particle-laden sessile droplets.

Material assembly by droplet drying: From mechanics theories to applications

“…For example, experiments on water droplets with drying temperature from room to near boiling point temperature (90°C) demonstrate that polystyrene nanospheres accumulate at the air-liquid interface rather than at the droplet edge. 106 F I G U R E 4 Deposition patterns obtained after evaporation of sessile droplets in different drying environments. (a) Ambient pressure.…”

“…Similar findings have also been obtained when the ambient temperature changes. For example, experiments on water droplets with drying temperature from room to near boiling point temperature (90°C) demonstrate that polystyrene nanospheres accumulate at the air–liquid interface rather than at the droplet edge 106 …”

Controlling Spatial Morphology of Microparticle Deposits via Thermocapillary Flows: Effect of Boundary Geometry

“…Controlling the propagation of the contact line of an evaporating colloidal droplet by setting various microtextures on substrates in the form of a distribution of micropillars with arbitrary cross-sectional shape or micropyramidal depressions and others is one of the popular methods . Droplet evaporation on such surfaces occurs with pinning of the contact line on surface features allowing to create particle distribution contours close to a square, hexagonal, and octagonal shapes. − However, a peculiarity of this approach is that the particles are deposited in the hollows of the substrate structure. Recently reported the creation of triangle-, circle-, and square-shaped patterns using composite smooth substrates with different wettability.…”

Viscous-capillary entrainment on bioinspired millimetric structure for sustained liquid transfer

“…The lack of research is partly due to a lack of fabrication method and the complexity of dynamic effects involved at the millimetric scale. With the development of advanced manufacturing in recent years, such as three-dimensional (3D) printing, chemical and optical etching, and precision sculpting, the millimetric structured surfaces are designed and applied to open fluidics (29)(30)(31), thermal control (32,33), and wet state adjustment (34,35) to achieve higher efficiency than macro-or microstructures. Therefore, an in-depth study on the dynamic properties of the bio-inspired millimetric structure-modified entraining will lead to insight into the one-century-old question of liquid entrainment and provide possibilities for liquid transfer.…”