Advances in microfluidic emulsification have enabled the creation of multiphase emulsion drops, which have emerged as promising templates for producing functional microcapsules. However, most previous micro‐encapsulation methods have limitations in terms of capsule stability, functionality, and simplicity of fabrication procedures. Here, we report a simple single‐step encapsulation technique that uses an optofluidic platform to efficiently and precisely encapsulate a specific number of emulsion droplets in photocurable shell droplets. In particular, we show, for the first time, that densely confined core droplets within an oily shell droplet rearrange into a unique configuration that minimizes the interfacial energy, as confirmed here from theory. These structures are then consolidated into multi‐cored microcapsules with structural and mechanical stability through in situ photopolymerization of the shell in a continuous mode, which are capable of isolating active materials and releasing them in a controlled manner using well‐defined nanohole arrays or nanoscopic silver architectures on thin membranes.

Noniridescent structural color pigments have great potential as alternatives to conventional chemical color pigments in many coloration applications due to their nonbleaching and color-tunable properties. In this work, we report a novel method to create photonic microgranules composed of glassy packing of silica particles and small fraction of carbon black nanoparticles, which show pronounced structural colors with low angle-dependency. To prepare isotropic random packing in each microgranule, a Leidenfrost drop, which is a drop levitated by its own vapor on a hot surface, is employed as a template for fast consolidation of silica particles. The drop randomly migrates over the hot surface and rapidly shrinks, while maintaining its spherical shape, thereby consolidating silica particles to granular structures. Carbon black nanoparticles incorporated in the microgranules suppress incoherent multiple scattering, thereby providing improved color contrast. Therefore, photonic microgranules in a full visible range can be prepared by adjusting the size of silica particles with insignificant whitening.

A facile PDMS-glass hybrid microfluidic device is developed for generating uniform submicrometer-scale double emulsion droplets with unprecedented simplicity and controllability. Compared with planar flow-focusing geometries, our three-dimensional flow-focusing geometry is advantageous for stably producing femto- to atto-liter droplets without the retraction problem of the dispersed phase fluid. In addition, this microfluidic platform can withstand the use of strong organic solvents (e.g. tetrahydrofuran (THF) and toluene) as a dispersed phase without deforming PDMS devices because the dispersed phase containing organic solvents does not directly contact the PDMS wall. In particular, monodisperse double emulsions are generated spontaneously via the internal phase separation of single emulsions driven by the diffusion of a co-solvent (tetrahydrofuran) in microfluidic devices. Finally, we demonstrated that the double emulsions can be used as morphological templates of ultrafine spherical silica capsules with controlled hierarchical pore networks via the evaporation-induced self-assembly (EISA) method. During EISA, triblock copolymers (Pluronic F127) act as a surfactant barrier separating the internal droplet from the continuous oil phase, resulting in the 'inverse' morphology (i.e. hydrophobic polymer-in-water-in-oil emulsions). Depending on the precursor composition and kinetic condition, various structural and morphological features, such as mesoporous hollow silica spheres with a single central core, multi-cores, or a combination of these with robust controllability can be seen. Electron microscopy (SEM, STEM, HR-TEM), small angle X-ray scattering (SAXS), and N(2) adsorption-desorption confirm the well-controlled hierarchical pore structure of the resulting particles.

Nanoscale floating-gate characteristics of colloidal Au nanoparticles electrostatically assembled on Si nanowires have been investigated. Colloidal Au nanoparticles with ∼5nm diameters were selectively deposited onto the lithographically defined n-type Si nanowire surface by 2min electrophoresis between the channel and the side gates. The device transfer characteristics measured at room temperature showed hysteresis, with the depletion mode cutoff voltage applied by the side gates shifted by as much as 1.5V, with the source-drain bias at 1.4V. The results demonstrate that the electrostatic assembly of colloidal Au nanoparticles is a useful method for the fabrication of Si nanowire based nanoscale floating-gate nonvolatile memory structures.

Colloidal crystals and their derivatives have been intensively studied and developed during the past two decades due to their unique photonic band gap properties. However, complex fabrication procedures and low mechanical stability severely limit their practical uses. Here, we report stable photonic structures created by using colloidal building blocks composed of an inorganic core and an organic shell. The core-shell particles are convectively assembled into an opal structure, which is then subjected to thermal annealing. During the heat treatment, the inorganic cores, which are insensitive to heat, retain their regular arrangement in a face-centered cubic lattice, while the organic shells are partially fused with their neighbors; this forms a monolithic structure with high mechanical stability. The interparticle distance and therefore stop band position are precisely controlled by the annealing time; the distance decreases and the stop band blue shifts during the annealing. The composite films can be further treated to give a high contrast in the refractive index. The inorganic cores are selectively removed from the composite by wet etching, thereby providing an organic film containing regular arrays of air cavities. The high refractive index contrast of the porous structure gives rise to pronounced structural colors and high reflectivity at the stop band position.

Advances in microfluidic emulsification have enabled the creation of multiphase emulsion drops, which have emerged as promising templates for producing functional microcapsules. However, most previous micro‐encapsulation methods have limitations in terms of capsule stability, functionality, and simplicity of fabrication procedures. Here, we report a simple single‐step encapsulation technique that uses an optofluidic platform to efficiently and precisely encapsulate a specific number of emulsion droplets in photocurable shell droplets. In particular, we show, for the first time, that densely confined core droplets within an oily shell droplet rearrange into a unique configuration that minimizes the interfacial energy, as confirmed here from theory. These structures are then consolidated into multi‐cored microcapsules with structural and mechanical stability through in situ photopolymerization of the shell in a continuous mode, which are capable of isolating active materials and releasing them in a controlled manner using well‐defined nanohole arrays or nanoscopic silver architectures on thin membranes.