Self-propelled swimming droplets

Ionic liquid-in-water emulsions stabilized by molecular and polymeric surfactants

“…We further report active self-propulsion of IL droplets, arising due to spontaneously generated Marangoni flow, which has not been previously reported in ILs but is commonly observed in alkanes and haloalkanes. 63,65,66,69,70 Further, we report the discovery of a type of spontaneous emulsification resulting in the development of double and triple emulsions in select ILs in which water is highly soluble, facilitated by surfactants possessing SDS-like chemical structure. Strategies to control the spontaneous formation of double emulsions may prove particularly useful for encapsulation applications.…”

Dynamics of Active SiO2–Pt Janus Colloids in Dilute Poly(ethylene oxide) Solutions

“…Here, spontaneously generated Marangoni stresses at the droplet interface lead to their propulsion. 3 While the propulsion mechanisms mentioned above may differ among the different artificial swimmers, their characteristics remain the same: a directed ballistic motion at short time scales followed by a random motion at longer time scales. 12,21 However, the translational and rotational diffusivities depend on various parameters such as swimmer size, 22 the magnitude of the propulsion force 12,23 and also the presence of solutes in the surrounding medium.…”

“…Garnering inspiration from micro-organisms such as bacteria, algae, and spermatozoa, over the past couple of decades, researchers have devised artificial micro-swimmers . − By utilizing an in-built mechanism which breaks the symmetry of their interactions with the surrounding medium, these artificial machines can perform autonomous motion analogous to the locomotion of microorganisms. On choosing appropriate chemistry, they typically self-generate either a chemical or a physical gradient in their vicinity, which drives their motion.…”

“…The resultant asymmetric concentration gradient of the reaction products causes the JCs to propel in the direction away from the metal through a mechanism known as self-diffusiophoresis . − JCs have also been known to propel under a self-generated electric potential ( self-electrophoresis ) , or a temperature gradient ( self-thermophoresis ). − The other widely recognized class of artificial swimmers consist of dispersed droplets self-propelling in the continuous phase in the presence of surfactants. Here, spontaneously generated Marangoni stresses at the droplet interface lead to their propulsion . While the propulsion mechanisms mentioned above may differ among the different artificial swimmers, their characteristics remain the same: a directed ballistic motion at short time scales followed by a random motion at longer time scales. , However, the translational and rotational diffusivities depend on various parameters such as swimmer size, the magnitude of the propulsion force , and also the presence of solutes in the surrounding medium. − Microswimmer–wall effects have also been known to affect the motion characteristics significantly. − Self-propelled JCs have been studied by subjecting them to diversified environments such as externally imposed flow, − topological obstacles, , and fluid interfaces ,, or placing them in a pool of passive tracers. − Recent studies have also demonstrated tuning of the dynamics of active JCs by altering their surface morphologies. , …”

Arrested on heating: controlling the motility of active droplets by temperature

“…This kind of control is important in the design and study of artificial and biological microswimmers, their theoretical modelling, experimental realisation, and, ultimately, to provide design principles and dynamic control for technological application. Autophoretic particles [2][3][4][5] and, particularly, their experimental realisation by active droplets [6][7][8][9][10][11][12][13][14][15] are popular active matter models driven by purely physicochemical mechanisms. Generally, their dynamics are characterized by a dimensionless Péclet number Pe, quantifying the ratio of advective and diffusive transport of chemical fuel [16].…”