Chemically Tuning Attractive and Repulsive Interactions between Solubilizing Oil Droplets

Abstract

Micellar solubilization is a transport process occurring in surfactant-stabilized emulsions that can lead to Marangoni flow and droplet motility. Active droplets exhibit self-propulsion and pairwise repulsion due to solubilization processes and/or solubilization products raising the droplet's interfacial tension. Here, we report emulsions with the opposite behavior, wherein solubilization decreases the interfacial tension and causes droplets to attract. We characterize the influence of oil chemical structure, nonionic surfactant structure, and surfactant concentration on the interfacial tensions and Marangoni flows of solubilizing oil-in-water drops. Three regimes corresponding to droplet "attraction", "repulsion" or "inactivity" are identified. We believe these studies contribute to a fundamental understanding of solubilization processes in emulsions and provide guidance as to how chemical parameters can influence the dynamics and chemotactic interactions between active droplets.

Marangoni Droplets of Dextran in PEG Solution and Its Motile Change Due to Coil–Globule Transition of Coexisting DNA

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Nanorobotic System with Fine Control over Multiple Modes of Motion

“…While multiple approaches of powering nanorobots have been developed including chemical, − electrical, − magnetic, − acoustic, − and electromagnetic, − most of these methods, coupled with a particular nanorobot design, yield either primarily a translational mode of motion or a rotational one. Recognizing the need to expand nanorobot range of motion to increase their functionality has led to an increasing effort directed at using dual actuation methods. − Previous reports on dually actuated motors have used acoustic propulsion or chemical propulsion as one of the methods of propulsion. − Reports, where one of the actuation methods is acoustic propulsion, have primarily focused on the ability to control the direction of motion of linearly propelling nanorobots, demonstrating directional reversal when switching between one method of actuation and another but have demonstrated no rotational modes of motion. − Reports of methods where one of the actuation methods utilizes a chemical fuel, − typically hydrogen peroxide, suffer from the rapid depletion of the chemical fuel during operation, which influences the mode of motion in an uncontrolled way.…”