No abstract

Directed self-assembly can produce ordered or organized superstructures from pre-existing building blocks through pre-programmed interactions. Encoding desired information into building blocks with specific directionality and strength, however, poses a significant challenge for the development of self-assembled superstructures. Here, we demonstrate that controlling the shape and patchiness of particles trapped at the air-water interface can represent a powerful approach for forming ordered macroscopic complex structures through capillary interactions. We designed hexagram particles using a micromolding method that allowed for precise control over the shape and, more importantly, the chemical patchiness of the particles. The assembly behaviors of these hexagram particles at the air-water interface were strongly affected by chemical patchiness. In particular, two-dimensional millimeter-scale ordered structures could be formed by varying the patchiness of the hexagram particles, and we attribute this effect to the delicate balance between the attractive and repulsive interactions among the patchy hexagram particles. Our results provide important clues for encoding information into patchy particles to achieve macroscopic assemblies via a simple molding technique and potentially pave a new pathway for the programmable assembly of particles at the air-water interface.

In the present work, the phenomenon of droplet formation by dripping at a micro T-junction in liquid-liquid mixing was studied experimentally. The drop formation process consisted of three stages: the X-Y growth, X growth, and the detachment stages. In the X-Y growth stage, the bulged part of the disperse phase grows both in X (parallel to the main channel) and Y (lateral to the main channel) directions. The X-Y growth stage is followed by the X growth stage where the bulged part grows only in the main channel direction. Subsequently, in the detachment stage, the drag force exerted by the continuous phase becomes larger than the surface tension force between the two phases and the bulged part is finally separated into a droplet with regular intervals through a rapid necking process. Droplet sizes were estimated from the drop generation frequency and the flow rate of the disperse phase, and were also confirmed by direct measurements through photography. The sizes of the micro droplets generally decrease with the larger flow rate of the continuous phase or with a smaller flow rate of the disperse phase. This is due to the increase of the interfacial shear force between the two phases through the increase in the relative velocity. The droplet size also decreases with increase of the viscosity of the either phase. This again is due to the increase of the interfacial shear force (and hence the drag force) between the phases when the viscosity of either phase becomes large. The measured drop sizes will serve as a set of the benchmarking data for the development of a droplet detachment model in the dripping mode at micro T-junctions.

Polydimethyl-siloxane (PDMS) is often applied to fabricate cell chips. In this study, we fabricated an adipocyte microcell pattern chips using PDMS to analyze the inhibition activity of lipid droplets in mouse embryo fibroblast cells (3T3-L1) with anti-obesity agents. To form the PDMS based micropattern, we applied the micro-contact printing technique using PDMS micro-stamps that had been fabricated by conventional soft lithography. This PDMS micro-pattern enabled the selective growth of 3T3-L1 cells onto the specific region by preventing cell adhesion on the PDMS region. It then allowed growth of the 3T3-L1 cells in the chip for 10 days and confirmed that lipid droplets were formed in the 3T3-L1 cells. After treatment of orlistat and quercetin were treated in an adipocyte micro-cell pattern chip with 3T3-L1 cells for six days, we found that orlistat and quercetin exhibited fat inhibition capacities of 19.3% and 24.4% from 0.2 μM of lipid droplets in 3T3-L1 cells. In addition, we conducted a direct quantitative analysis of 3T3-L1 cell differentiation using Oil Red O staining. In conclusion, PDMS-based adipocyte micro-cell pattern chips may contribute to the development of novel bioactive compounds.