We present a technique for the continuous interphase synthesis of metal oxide nanoparticles using a droplet flow reactor. Conducting the synthesis reaction inside droplets of controlled volume offers several advantages, such as eliminating temperature and concentration gradients inside the reactor as well as preventing reactor fouling. The synthesis reagents are initially located in separate phases, and reagent addition is accomplished through diffusion from the bulk phase to the droplet phase. In this work, the technique is demonstrated by synthesizing zinc oxide nanoparticles inside aqueous droplets containing zinc acetate in a bulk stream of sodium hydroxide in 1-octanol. This flow synthesis of zinc oxide nanoparticles provides more control of the nanoparticle morphology and has a narrow particle size distribution as compared to that of a batch reactor. The size and morphology of the nanoparticles are shown to be easily controlled from 41 to 62 nm by varying zinc acetate and sodium hydroxide concentration, reaction temperature, and residence time. Spherical as well as platelike shapes of zinc oxide nanoparticles are seen for the ranges of parameters studied. This technique can be used to synthesize a variety of metal oxide nanoparticles of controllable size.

A millifluidic polyol process was used to produce high aspect ratio silver nanowires (AgNWs) with high selectivity. For comparison, AgNWs were synthesized in both a batch reactor and a continuous millifluidic reactor. The wires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Energy-dispersive X-ray (EDX) spectroscopy and UV-Visible (UV-Vis) spectroscopy. The effect of temperature was investigated to optimize morphology and selectivity. High selectivity of very long and thin AgNWs was obtained in the millifluidic reactor. In comparison with the batch reactor, superior selectivity and aspect ratios were obtained in the millifluidic reactor, and a lower operating temperature could be used. The effect of residence time (flow rate) on the diameter and length of the synthesized AgNWs was investigated. Finally, Reynolds and Peclet number were calculated to investigate the silver nanostructures flow behavior during the course of synthesis.

Calcium alginate films generally offer poor diffusion resistance to water. In this study, we present a technique for encapsulating aqueous drops in a modified calcium alginate membrane made from an emulsion of silicone oil and aqueous alginate solution and explore its effect on the loss of water from the capsule cores. The capsule membrane storage modulus increases as the initial concentration of oil in the emulsion is increased. The water barrier properties of the fabricated capsules were determined by observing the mass loss of capsules in a controlled environment. It was found that capsules made with emulsions containing 50 wt% silicone oil were robust while taking at least twice the time to dry completely as compared to capsules made from only an aqueous alginate solution. The size of the oil droplets in the emulsion also has an effect on the water barrier properties of the fabricated capsules. This study demonstrates a facile method of producing aqueous core alginate capsules with a modified membrane that improves the diffusion resistance to water and can have a wide range of applications.

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