Ya-Wen Chang

Pickering emulsions stabilized by amphiphilic nano-sheets

We demonstrate the fabrication of amphiphilic nano-sheets, which are either surface- or edge-modified plates with thickness at the atomic scale, one of the thinnest amphiphilic particles reported so far. They are obtained by exfoliation of functionalized layered crystals, the first time that laminar structures have been utilized to produce such particles. Stable emulsions were made utilizing these nano-sheets. The adsorption of the amphiphilic nano-sheets onto the oil-in-water interfaces and the reduction of surface tension between the PDMS and the amphiphilic nano-sheet suspensions were quantitatively characterized.

Stabilization of Pickering foams by high-aspect-ratio nano-sheets

We developed Pickering foams highly stabilized by high-aspect-ratio (ξ = diameter/thickness) nano-sheets. The effects of particle aspect ratio, concentration, and hydrophobicity were also investigated. To our knowledge, our study provides the first experimental evidence of the effect of particle aspect ratio on particle-stabilized foams. The adsorption properties of these highly anisotropic nano-sheets are strongly affected by their small thickness and large lateral size (i.e., two-dimensional). These high-aspect-ratio nano-sheets were obtained by exfoliation of α-zirconium phosphate (ZrP) crystals with propylamine (C3H7NH2, PA). The hydrophobicity of the nano-sheets was tailored by adjusting the PA : ZrP molar ratio in the suspension. The morphology and stability of the foam depend on the nano-sheet aspect ratio and concentration as well as on the PA : ZrP molar ratio. Here, we found that using low and high aspect ratio nano-sheets having a high and an intermediate degree of hydrophobicity, respectively, is the successful formula to obtain high foam stability. The aqueous foams were characterized by optical and cross-polarized micrographs. Scanning electron microscopy (SEM) micrographs of dried foams revealed the adsorption of the PA–ZrP nano-sheets on the air–water interface. The foam stability was studied by measuring the foam and the water volume as a function of time to obtain the foam decay and water drainage rate, respectively. We also observed that the foams were stabilized by jammed layers of nano-sheets located in the bulk and at the air–water interface. These layers of particles prevent air diffusion between the bubbles, hence arresting Ostwald ripening and coalescence.

Hydrothermal synthesis of layered α-zirconium phosphate disks: control of aspect ratio and polydispersity for nano-architecture

The crystals of layered compounds are normally in the shape of disks or plates. Systematic experiments revealed that regular-shaped α-zirconium phosphate crystalline disks with a size-to-thickness ratio from 1 to 50 and size polydispersity as low as 0.2 can be obtained through hydrothermal treatment in 3 M to 15 M phosphoric acid solutions. Transmission and scanning electron micrographs revealed that the growth of the disks is mediated by oriented attachment, which happened continuously throughout the hydrothermal treatment between various sized disks. Ostwald ripening is effective in improving the regularity of the shape of the disks, especially under prolonged hydrothermal treatment. Preferred attachment among the flat surfaces of the disks leads to the diverse developments of their size and thickness polydispersities.

Uniform yeast cell assembly via microfluidics.

This paper reports the use of microfluidic approaches for the fabrication of yeastosomes (yeast-celloidosomes) based on self-assembly of yeast cells onto liquid-solid or liquid-gas interfaces. Precise control over fluidic flows in droplet- and bubble-forming microfluidic devices allows production of monodispersed, size-selected templates. The general strategy to organize and assemble living cells is to tune electrostatic attractions between the template (gel or gas core) and the cells via surface charging. Layer-by-Layer (LbL) polyelectrolyte deposition was employed to invert or enhance charges of solid surfaces. We demonstrated the ability to produce high-quality, monolayer-shelled yeastosome structures under proper conditions when sufficient electrostatic driving forces are present. The combination of microfluidic fabrication with cell self-assembly enables a versatile platform for designing synthetic hierarchy bio-structures.