Microfluidic droplet generation based on non-embedded co-flow-focusing using 3D printed nozzle

Abstract

Most commercial microfluidic droplet generators rely on the planar flow-focusing configuration implemented in polymer or glass chips. The planar geometry, however, suffers from many limitations and drawbacks, such as the need of specific coatings or the use of dedicated surfactants, depending on the fluids in play. On the contrary, and thanks to their axisymmetric geometry, glass capillary-based droplet generators are a priori not fluid-dependent. Nevertheless, they have never reached the market because their assembly requires fastidious and not scalable fabrication techniques. Here we present a new device, called Raydrop, based on the alignment of two capillaries immersed in a pressurized chamber containing the continuous phase. The dispersed phase exits one of the capillaries through a 3D-printed nozzle placed in front of the extraction capillary for collecting the droplets. This non-embedded implementation of an axisymmetric flow-focusing is referred to non-embedded co-flow-focusing configuration. Experimental results demonstrate the universality of the device in terms of the variety of fluids that can be emulsified, as well as the range of droplet radii that can be obtained, without neither the need of surfactant nor coating. Additionally, numerical computations of the Navier-Stokes equations based on the quasi-steadiness assumption allow to provide an explanation to the underlying mechanism behind the drop formation and the mechanism of the dripping to jetting transition. Excellent predictions were also obtained for the droplet radius, as well as for the dripping-jetting transition, when varying the geometrical and fluid parameters, showing the ability of this configuration to enventually enhance the dripping regime. The monodispersity ensured by the dripping regime, the robustness of the fabrication technique, the optimization capabilities from the numerical modelling and the universality of the configuration confer to the Raydrop technology a very high potential in the race towards high-throughput droplet generation processes.

An alternative choice of the boundary condition for the arbitrary Lagrangian-Eulerian method

“…It is worth mentioning that, since the DBALE method is firstly proposed here, the few examples are previous and recent works of the authors. In addition, in the work [10] we have found that ABALE method not only leads to large mesh distortion but is also very limited by (8). Last, the explicit surface description falls in the same category as ABALE method.…”

“…5. Solution of ( 14) for the velocity field (15) using (a) BE (5b) or BL (3b) and (b) DBALE (6b), (10). Because of the symmetry, only the first quadrant has been plotted.…”

“…In this subsection, we solve two practical examples using the DBALE method. The first one is about a bubble flowing in a microchannel [45,46] and the second is about bubble formation in a microfluidic device [10]. The details on the modelling and the results are given in those references but we focus here on the mesh deformation and the comparison between the DBALE methods and the other ones.…”

“…In addition, if this method treats this displacement as an unknown variable, existing solvers could be used reducing the effort to implement such a method. In this work, we provide this method, that has been successfully used in previous works [45,46,10].…”

Statics and dynamics of a viscous ligament drawn out of a pure-liquid bath

“…2013; Martínez-Calvo, Rubio-Rubio & Sevilla 2018) or by viscous stresses (Dewandre et al. 2020) have been extensively studied, and three distinct regimes can be identified by the flow rate provided by the nozzle: a periodic dripping regime for low flow rates, a dripping faucet regime for intermediate flow rates and a jetting regime for high flow rates. (ii) Ligaments stretched between two disks, mainly one of the disks being pulled up at a constant velocity or acceleration, have been studied by Zhang, Padgett & Basaran (1996), Vincent, Duchemin & Villermaux (2014 b ), Zhuang & Ju (2015), Wylie, Bradshaw-Hajek & Stokes (2016) and Brulin, Tropea & Roisman (2020).…”