Liter-scale production of uniform gas bubbles via parallelization of flow-focusing generators

Abstract

Microscale gas bubbles have demonstrated enormous utility as versatile templates for the synthesis of functional materials in medicine, ultra-lightweight materials and acoustic metamaterials. In many of these applications, high uniformity of the size of the gas bubbles is critical to achieve the desired properties and functionality. While microfluidics have been used with success to create gas bubbles that have a uniformity not achievable using conventional methods, the inherently low volumetric flow rate of microfluidics has limited its use in most applications. Parallelization of liquid droplet generators, in which many droplet generators are incorporated onto a single chip, has shown great promise for the large scale production of monodisperse liquid emulsion droplets. However, the scale-up of monodisperse gas bubbles using such an approach has remained a challenge because of possible coupling between parallel bubbles generators and feedback effects from the downstream channels. In this report, we systematically investigate the effect of factors such as viscosity of the continuous phase, Capillary number, and gas pressure as well as the channel uniformity on the size distribution of gas bubbles in a parallelized microfluidic device. We show that, by optimizing the flow conditions, a device with 400 parallel flow focusing generators on a footprint of 5 × 5 cm2 can be used to generate gas bubbles with a coefficient of variation of less than 5% at a production rate of approximately 1 L/hr. Our results suggest that the optimization of flow conditions using a device with a small number (e.g., 8) of parallel FFGs can facilitate large-scale bubble production.

Silicon and glass very large scale microfluidic droplet integration for terascale generation of polymer microparticles

“…In previous work, architectures have been developed that make it possible to operate many microfluidic droplet generators in parallel 11 – 22 . While great progress has been made in these approaches, current chips with parallelized devices are limited to production rates ϕ max ⪍ 1 L h −1 , have droplet homogeneities set by three-dimensional (3D) soft-lithography fabrication 15 , are limited to low temperature and pressure operation, can only be used with the solvents compatible with the device’s polymer construction, or are unable to be adapted to produce higher-order emulsions and particles that require multi-step processing 23 – 25 .…”

Large-Scale Production of Compound Bubbles Using Parallelized Microfluidics for Efficient Extraction of Metal Ions

“…To ensure that the fluid flow rates are uniform throughout the device, we use the previously reported ladder geometry, which has proven to be a robust approach to enable large-scale production of simple emulsions and bubbles. 19,21 Briefly, gas, water and oil phases are introduced into the device through respective inlets and divided into 8 sets of distribution channels that run horizontally as illustrated in Figure 1 width, height and length of the channel and the viscosity of the fluid). 40 This criteria states that the resistance of distribution channel (R d ) between two adjacent FFGs should be significantly smaller than the resistance of a single FFG (R f ).…”

“…Our previous study on the parallelization of simple gas bubble production has shown that it is helpful to use a device with a smaller number of parallel FFGs to study the effect of fluid flow rates on the size and uniformity of produced emulsions or bubbles to identify ideal flow rates that will lead to stable emulsion formation, and that these flow conditions can be used successfully in devices with greater numbers of FFGs. 21 In this work, we use the same strategy to find optimal flow conditions. Specifically, we use a device with 8 parallel FFGs to study how the changes in the flow rates influence the formation of G/W/O compound bubbles and their uniformity.…”

“…As described in our previous report, three dimensional microfluidic networks can be fabricated using a double-sided imprinting method that molds a three dimensional microfluidic chip in one-step by sandwiching PDMS between a hard silicon master and a soft PDMS master. 19,21 These masters can be formed by conventional photo-and soft-lithography. Briefly, we prepare the triple-height hard master by photo-lithography using SU-8 3000 photoresist (MicroChem Corporation) on a silicon substrate.…”

“…[12][13][14] The prospect of translating these laboratory-scale demonstrations into commercial success has been further heightened by the recent advances in the large-scale production of droplets and bubbles using parallelized microfluidic generators. [15][16][17][18][19][20][21][22] One important class of multiphasic fluid dispersions that microfluidics are uniquely well suited to produce are ternary compound bubbles. [23][24][25] Because emulsions in a microfluidic device are precisely fabricated one particle at a time, highly monodispersed multi-order emulsions and bubbles can be generated with precise control.…”