Yflow® has been specialized in the CoFlowing (Coaxial Flowing) technique thanks to the collaboration with the Soft Condensed Matter Laboratory (School of Physics, Georgia Tech, USA) along with the development of private-consortium projects where capsules in the range of 1-50 microns were desired.

CoFlowing consists of using the drag of a moving fluid on a meniscus from another fluid which is immiscible with the drag and is injected through a capillary tube. Depending on the conditions (liquids properties, geometry of tubes,…) monodisperse microspheres, microcapsules or microfibers significantly lower than that of the fluid injected hole diameters can be obtained.


Picture that shows how the outer liquid drags to the inner, which breaks into micro-droplets.

When the inner and outer flow rates are low for both fluids a system of dripping is produced just at the end of the injection tube (droplets are typically generated periodically).


Co-Flowing in the Dripping mode.

However with the higher liquid flow outside the inner fluid is more stretched into long filaments or jets liquids (jetting mode) that due to varicose instabilities breaks into droplets. In the jetting mode two regimes can be identified: the narrowing regime, in which the filament diameter decreases axially, and the widening regime, in which the filament diameter increases axially. Narrowing jets are formed when viscous forces acting on the jet surface due to the outer jet, the drag liquid, overcomes the forces of confinement due to surface tension , where the inertia of the inner fluid is negligible. In these situations, the jet narrowing occurs due to the inner speed is higher than the outer speed. On the other hand, widening jets are produced when the forces due to the inertia of the inner flow exceed confinement forces due to surface tension. By contrast, the internal fluid flows faster than the outside, which is responsible for producing a slow jet widening thereof.


Co-Flowing in the Jetting mode: (a) Narrowing and (b) Widening.

Video Performance of CoFlowing Tech.

Including another outer coaxial channel it is possible to generate fibered or spherical microcapsules in the nanometric range. This technique is called Coaxial CoFlowing.

coflowinggsetup coflowing

Picture of microencapsulation process by Coaxial CoFlowing and Sketch of Coaxial CoFlowing setup.

Yflow® has gathered a deep know-how related to designing, optimizing, characterization and production of droplets, bubbles and fibers in the micron range using Coaxial Co-Flowing.


Example of Coaxial Co-Flowing device made in Yflow with microforge and a puller from glass capillaries.

Video Performance of Coaxial CoFlowing Tech.

Another approach of production of droplets, particles and capsules in the micron range is Confined Selective Withdrawal, a technique developed in Yflow® S.D. that uses a setup very similar to Coaxial Co-Flowing. It also uses a Core Fluid, a Shell Fluid and the Focusing Liquid (drags and focuses the capsules) to the end of the tip.

selective withdrawal

Sketch of Selective Withdrawal setup

Yflow offers its customers access to this technology for basic or applied research, but also to integrate it in their own labs. To achieve this we employ the latest equipment that allow the fabrication of microfluidics devices.

– Puller (stretching of capillars to desired diameter)

– Microforge (cutting of capillary tips to desired diameter).

– Molds and negative templates for the manufacture of printed circuit in PDMS.

– Mixer for preparation of PDMS solution.


Details of capillary tips of glass prepared in Yflow Lab.

Learn more about Microfluidics:

– C. N. Baroud, F. Gallaire, and R. Dagla.  Dynamics of microfluidic droplets. Lab Chip. 10: 2032-2045, 2010.

– E. Castro-Hernández, V. Gundabala, A. Fernández-Nieves, J.M. Gordillo.  Scaling the drop size in coflow experiments. New Journal of Physics. 11, 2009.

– Gundabala, V.R. and Vilanova, N. and Fernández-Nieves, A. Current-Voltage characteristic of electrospray processes in microfluidics. Physical Review Letters. 105(15), 2010.

– Vilanova, N. and Gundabala, V.R. and Fernandez-Nieves, A. Drop size control in electro-coflow. Applied Physics Letters. 99(2), 2011.

– Utada, A.S. and Fernandez-Nieves, A. and Stone, H.A. and Weitz, D.A. Dripping to jetting transitions in coflowing liquid streams. Physical Review Letters. 99(9), 2007.

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