Directional and velocity control of active droplets using a rigid-frame

Abstract

This paper introduces a novel directional control method of self-propelled oil droplets using an exoskeleton frame.

Analysis of different self-propulsion types of oil droplets based on electrostatic interaction effects

“…Yamada et al found that a single oil droplet changed into a boomerang shape when moving alone in a straight direction. 28 They succeeded to induce only the straight motion of an oil droplet by attaching it to a frame to shape it as a boomerang. A similar argument can be applied to our study.…”

“…Because oil droplets undergo different motions when their shape is changed by external stimuli, Yamada et al achieved motion control by applying external stimuli to oil droplets. 28 In other words, when repulsive motion occurs, the charged oil droplet experiences a repulsive force from the neighboring oil droplet as a result of electrical effects, and their shapes are distorted in opposite directions. The visualization of internal convection by PIV also confirmed that such a change of shape causes each oil droplet to generate a convection flow that results in them moving in opposite directions.…”

“…A pH gradient in the aqueous solution 19,20,27 and an exoskeleton frame 28 have been previously used to control the behavior of a single oil droplet. In the case of multiple oil droplets, Toyota et al reported two different behaviors of a pair of 4-octylaniline droplets containing 5 mol% of amphiphilic catalyst.…”

Smart Droplets Stabilized by Designer Surfactants: From Biomimicry to Active Motion to Materials Healing

“…Active droplet motion may be induced by mechanisms that break symmetry at the liquid-liquid interface as a result of chemical reactions, [137,138] surfactant adsorption or desorption, [139,140] solvent de-mixing, [141] and micelle solubilization. [131,142,143] Regardless of the origins of asymmetry, surface tension gradients (i.e., Marangoni forces) inside the droplet and within the continuous phase arise from differential surfactant concentrations that direct droplet motion opposite to that of fluid flow (Figure 18).…”

“…[24,[126][127][128][129][130][131][132] In this Section, we focus on striking examples of autonomous motion of soft synthetic systems that either arise spontaneously, referred to as active emulsions or which are stimuli-responsive, termed driven emulsions. We note that excellent descriptions of motion in conceptually related [137] Copyright 2019, Royal Society of Chemistry; B) Phase-contrast optical micrographs of the amoeba-like trajectory of O/W emulsion droplets stabilized by C16TAB, including the time-lapsed description. Scale bar, 30 μm.…”