Chemical programming of solubilizing, non-equilibrium active droplets

In this Account, we highlight our group’s efforts towards developing chemical frameworks for understanding active and interactive oil-in-water emulsions. How do the chemical properties and physical spatial organization of the oil, water, and surfactant combine to yield colloidal-scale active properties? Our group tackles this question by employing systematic studies of active behavior working across the chemical space of oils and surfactants to link molecular structure to active behavior. The Account begins with an introduction to the self-propulsion of single, isolated droplets and how by applying biases, such as with a gravitation field or interfacially adsorbed particles, drop speeds can be manipulated. Next, we illustrate that some droplets can be attractive, as well as self-propulsive / repulsive, which does not fall in line with the current understanding of the impact of oil-filled micelle gradients on interfacial tensions. The mechanisms by which oil-filled micelles influence interfacial tensions of non-equilibrium interfaces is poorly understood and requires deeper molecular understanding. Regardless, we extend our knowledge of droplet motility to design emulsions with non-reciprocal predator-prey interactions and describe dynamic self-organization that arises from the combination of reciprocal and non-reciprocal interactions between droplets. Finally, we highlight our group’s progress towards answering key chemical questions surrounding non-equilibrium processes in emulsions that remain to be answered. We hope that our progress in understanding the chemical principles governing the dynamic non-equilibrium properties of oil-in-water droplets can help inform research in tangential research areas such as cell biology and origin-of-life.