The generation of monodisperse tracer particles is a crucial element of particle image velocimetry (PIV) flow measurements, but most commercially available particles are expensive to purchase, difficult to manufacture in-house, or fail to provide the neutral or near-neutral buoyancy needed to obtain unbiased velocity measurements. In this study, we seek to generate custom PIV particles by a double-emulsion method, in which the density and light-reflecting or light-emitting properties of the tracer droplets can be modified with relative ease and the monodispersity of the droplets can be controlled. The double emulsion droplets are generated by a co-flow microfluidic device. The micro-capillary device consists of cylindrical glass capillaries nested inside a square capillary. This involves a single step generation of double emulsions with precise control over size of the droplets.
The formation of double emulsion droplets is via two mechanisms i.e, dripping and jetting. In the dripping regime, the droplet forms close to the entrance of the collector capillary whereas in the jetting regime the inner and the middle fluid form a co-axial jet which extends two and more capillary diameters and breaks into a chain of double emulsion droplets. The flow rates and fluid properties of the droplet manufacturing process were optimized and the effect of density modification by salt addition was studied. The double emulsion droplets are polymerized using photo-polymerization techniques. Finally, the droplets were used in preliminary PIV measurements.
