Several works in the recent literature have reported successful achievement of microfluidic templated porous materials with a higher degree of regularity and improved performance as compared to, say, classical sponges. The design of such materials faces with numerous challenges, such as sustained production rate, as demanded by industrial applications, broad range of viscosities and polydispersity. The full-scale simulation of such devices at a molecular level will shed unprecedented insights into the complex physical mechanisms which control the macroscopic properties of these materials.
We plan to perform full-scale simulations of flow-focusing microfluidic devices aimed at generating highly regular bubble configurations of oil/water emulsions. The prototypical device consists of a planar flow focusing circuit, integrated within a microchip about 1 mm in length and 300 microns in width (see Figure from Costantini, et Al. J. Mater. Chem. B 2014, 2, 2290). The oil phase flows from the inlet chamber and mixes with the two streams of water from the top and bottom directions. Immediately downstream the channels which deliver the two phases, there is an orifice which forces the oil phase to inflate oil droplets in the outlet channel and release a droplet under the squeezing effects of the water cross-streams from above and below.
The typical size of the device is of the order of mm, with droplets diameter of the order of 100 microns. As a result, full resolution of the droplets requires a mesh spacing below 1 micron, mandating of the order of a billion mesh points for the full-scale simulation of the device.
Such resolution, however, falls short of capturing the details of the near-contact and contact many-body interactions between the droplets, which is where the crucial microphysics takes place. This is where special multiscale capabilities will be deployed. We shall perform an extensive set of simulations by varying the flow rates by changing the inlet velocity of the flowing phases and the size and shape of the microfluidic device, as well as surfactant concentrations, so as to identify the best operational conditions to deliver the most regular porous configurations.