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Electric field manipulation of particles in leaky dielectric liquids

Rozynek Z., Castberg R., Kalicka A., Jankowski P., Garstecki P.

Archives of Mechanics

2015

Vol. 67, nr 5

385--399

Patchy colloidal capsules, i.e., hollow structures with permeable heterogeneous surfaces, possess advantageous properties when compared with their homogenous counterparts. For example, owing to specific interactions between patches they can self-assemble into complex structures to form functional materials. Fabrication of patchy colloidal capsules has long been theorized by scientists able to design different models, but the actual production of them remains a challenge. Here, we demonstrate how to manipulate colloidal particles on a surface of a droplet with electric fields. We present three examples of patchy structures formed via electrohydrodynamic microflows and electro-coalescence. In addition, we show electro-orientation of patchy capsules composed of both nonconductive polymeric particles and conductive silver coated particles. Finally, we discuss the importance of an appropriate selection of oils and particles.

Formation of bubbles and droplets in microfluidic systems

Garstecki P., Ganan-Calvo A.M., Whitesides G.M.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2005

Vol. 53, nr 4

361-372

This mini-review reports the recent advances in the hydrodynamic techniques for formation of bubbles of gas in liquid in microfluidic systems. Systems comprising ducts that have widths of the order of 100 micrometers produce suspensions of bubbles with narrow size distributions. Certain of these systems have the ability to tune the volume fraction of the gaseous phase - over the whole range from zero to one. The rate of flow of the liquids through the devices determines the mechanism of formation of the bubbles - from break-up controlled by the rate of flow of the liquid (at law capillary numbers, and in the presence of strong confinement by the walls of the microchannels), to dynamics dominated by inertial effects (at high Weber numbers). The region of transition between these two regimes exhibits nonlinear behaviours, with period doubling cascades and irregular bubbling as prominent examples. Microfluidic systems provide new and uniquely controlled methods for generation of bubbles, and offer potential applications in micro-tlow chemical processing, synthesis of materials, and fluidic optics.