Moving Droplets in 3D Using Light

Abstract

The emulation of the complex cellular and bacterial vesicles used to transport materials through fluids has the potential to add revolutionary capabilities to fluidic platforms. Although a number of artificial motile vesicles or microdroplets have been demonstrated previously, control over their movement in liquid in 3D has not been achieved. Here it is shown that by adding a chemical "fuel," a photoactive material, to the droplet, it can be moved in any direction (3D) in water using simple light sources without the need for additives in the water. The droplets can be made up of a range of solvents and move with speeds as high as 10.4 mm s toward or away from the irradiation source as a result of a light-induced isothermal change in interfacial tension (Marangoni flow). It is further demonstrated that more complex functions can be accomplished by merging a photoactive droplet with a droplet carrying a "cargo" and moving the new larger droplet to a "reactor" droplet where the cargo undergoes a chemical reaction. The control and versatility of this light-activated, motile droplet system will open up new possibilities for fluidic chemical transport and applications.

Phototaxis Motion Behavior of a Self‐propelled Submarine‐like Water Droplet Robot in Oil Solvent

“…Xiao et al. showed that by adding a chemical “fuel,” a photoactive material, to the droplet, can move in any direction in water using simple light sources [47] …”

“…Fe 2 O 3 nanoparticles were synthesized by hydrothermal method. The detailed procedures were shown in Figure 4a [47, 48] . As shown in Figure 4a, firstly, 90 mL NaOH solution (6 M) was added dropwise into 100 mL FeCl 3 solution (2 M) under magnetic stirring.…”

Engineering motile aqueous phase-separated droplets via liposome stabilisation

“…The development of motile cell-mimetic compartmentalised systems is receiving increasing interest due to their potential in applications including targeted drug delivery 1,2,3 and environmental restoration 4,5 . The fact that controlled motility and chemotaxis is a behaviour that is considered to be one of the hallmarks of life has also made it a focus in the endeavour to construct artificial cells that mimic biological cells in form and function 6,7 .…”

“…To propel an object, various strategies have been exploited such as bubble-propulsion 8,9,10 , diffusiophoresis 11,12,13,14,15 , magnetic force 16,17 , and the Marangoni effect 18,19,20 . Among these methods, the Marangoni effect is a commonly used way to induce motion since it can be easily achieved 3 . The asymmetric distribution of interfacial tension (IFT) around a droplet spontaneously generates a Marangoni flow on the droplet surface, driving its motion.…”

“…A typical example of the Marangoni effect can be achieved by adopting a water/oil system, in which a water or oil drop can move in an oil or aqueous phase respectively by responding to changes in the droplet IFT 3,21,22,23 . For example, Xiao et al 3 reported that by adding photo-active surfactant precursors to an oil droplet, motion can be produced in an aqueous phase if one side of the oil droplet is irradiated by a light source to initiate a photo-responsive chemical and then generate an asymmetrical distribution of IFT. Li et al 23 reported that water/ethanol droplets can achieve motion in an oil phase containing squalene/monoolein.…”