Simulation of a Parallelizable Flow-Focusing Constant-Volume Droplet Generator

Microfluidic droplet generators offer distinctive advantages to create emulsions that cannot be matched by conventional methods such as membrane or batch emulsification[1]. Since microfluidic droplets are created in a confined and controlled space in a chip, they can be used as micro-reactors to perform delicate chemical reactions that take advantage of the scaling laws associated with miniaturization[2]. On of the main challenges that this technology has in order to be widely adopted in the industry is related with their scale-up and consequently volume production. A single chip can generate up to 10ml/hour of product. This can be enough for research settings but is far from being sustainable for industrial applications. [3], [4] Common microfluidic droplet generators, especially those known as flow-focusing generator, are very sensitive to the flowing rates of the continuous and disperse phases[5], [6]. Due to this strong dependence, parallelization of such devices is very challenging because one must ensure uniform flow distribution in a chip and minimize crosstalk and other interactions between them.[3] For this reason, other geometries that are less sensitive to the flowing rates have been proposed based on a common microfluidic T-juntion. [7] In this work, we have proposed a new constant-volume droplet generator based on a flowfocusing droplet generator instead. This new configuration has distinctive advantages over the classic T-juntion because the disperse phase is in lesser contact with the channels walls and therefore has lower probability of wetting these walls. We used the Laminar two-phase flow interface, from COMSOL Multiphysics software, to model this multiphase flow. Our simulations allowed us to simulate different geometries, and identify the key dimensions affecting the constant-droplet formation. Our results show a successful integration of a flow-focusing droplet generator with a geometrically set constant-volume generator. This integration will allow us to take the advantages of both types of devices into one. Reference [1] A. B. Theberge, F. Courtois, Y. Schaerli, M. Fischlechner, C. Abell, F. Hollfelder, and W. T. S. Huck, “Microdroplets in Microfluidics: An Evolving Platform for Discoveries in Chemestry and Biology,” Small, vol. 49, pp. 5846–5868, Mar. 2010. [2] N. J. Carroll, S. T. Chang, D. N. Petsev, and O. D. Velev, “Droplet Microreactors for Materials Synthesis,” Microdroplet Technology, 2012. [3] D. Conchouso, D. Castro, S. A. Khan, and I. G. Foulds, “Three-dimensional parallelization of microfluidic droplet generators for a litre per hour volume production of single emulsions,” Lab on a Chip, vol. 14, no. 16, pp. 3011–3020, 2014. [4] G. T. Vladisavljević, N. Khalid, M. A. Neves, T. Kuroiwa, M. Nakajima, K. Uemura, S. Ichikawa, and I. Kobayashi, “Industrial lab-on-a-chip: Design, applications and scale-up for drug discovery and delivery,” Advanced Drug Delivery Reviews, vol. 65, no. 11, pp. 1626–1663, Nov. 2013. [5] D. Conchouso, E. Rawashdeh, D. Castro, A. Arevalo, and I. G. Foulds, “Optimized Channel Geometry of a Flow-Focusing Droplet Generator for Parallelization.,” presented at the Proceedings of the 2013 COMSOL Conference, Rotterdam, 2013. [6] D. Conchouso, E. Al Rawashdeh, A. Arevalo, D. Castro, and I. G. Foulds, “Simulation of a 3D Flow-Focusing Capillary-Based Droplet Generator,” Proceedings of the 2013 COMSOL Conference. [7] V. van Steijn, P. M. Korczyk, L. Derzsi, A. R. Abate, D. A. Weitz, and P. Garstecki, “Blockand-break generation of microdroplets with fixed volume,” Biomicrofluidics, vol. 7, no. 2, p. 024108, 2013. Figures used in the abstract Figure 1: Simulation of a Flow-Focusing microfluidic device for constant volume droplet generation