The build-up of carbon dioxide in the atmosphere is one of the grand challenges facing society. Addressing this challenge by removing CO2 from the atmosphere or mitigating point source emissions through the separation and concentration of CO2 from these dilute sources requires reductions in energetic and monetary cost relative to traditional thermal and pressure swing methods. Electrochemical methods of CO2 separation have drawn increasing attention in recent years as potentially cheap, low-energy, scalable carbon capture technologies. In this Primer, we provide an overview of the experimentation and analysis needed for the study of electrochemical methods for CO2 separation, including a discussion of the considerations necessary for targeting the application of such techniques. This Primer focuses on ambient temperature techniques such as pH swing and direct redox processes, which utilize similar experimental set-ups. We include considerations on the choice of redox agent and an outlook on this growing body of research. Experimentation to address real-world conditions, particularly at practical oxygen concentrations, and novel system designs that overcome transport limitations or, potentially, couple capture and CO2 utilization are emerging areas in the field.

Nanoemulsions possess powerful nano-scale properties that make them attractive for diverse applications such as drug delivery, food supplements, nanoparticle synthesis and pharmaceutical formulation. However, there is little knowledge in nanoemulsion literature about controlling and predicting droplet size. In this article, we propose a scaling relation to predict the dependence of nanoemulsion droplet size with physical properties such as viscosity of the droplet phase and continuous phase, and process parameters such as input power density. We validate our proposed scaling with a wide range of droplet size data from nanoemulsions prepared with high pressure homogenization and ultrasonication. Our proposed scaling also compares favorably with experimental data from literature. The scaling relation can serve as a guiding principle for rational design of nanoemulsions.

Nanoemulsions are kinetically stable liquid-in-liquid dispersions with droplet sizes on the order of 100 nm. Their small size leads to useful properties such as high surface area per unit volume, robust stability, optically transparent appearance, and tunable rheology. Nanoemulsions are finding application in diverse areas such as drug delivery, food, cosmetics, pharmaceuticals, and material synthesis. Additionally, they serve as model systems to understand nanoscale colloidal dispersions. High and low energy methods are used to prepare nanoemulsions, including high pressure homogenization, ultrasonication, phase inversion temperature and emulsion inversion point, as well as recently developed approaches such as bubble bursting method. In this review article, we summarize the major methods to prepare nanoemulsions, theories to predict droplet size, physical conditions and chemical additives which affect droplet stability, and recent applications.