Our perspective article: Microfluidic synthesis as a new route to produce novel functional materials

“While the microfluidic synthesis of some specific types of products have been discussed elsewhere, the present perspective is organized in the angle of different enabling powers of microfluidic synthesis originated from the unique physical environment."

Link to the full article (open access): https://aip.scitation.org/doi/10.1063/5.0100206

By geometrically constraining fluids into sub-millimeter scale, microfluidics offers a physical environment largely different from macroscopic world, as a result of the significantly enhanced surface effects. This environment is characterized by laminar flow and inertial particle behavior, short diffusion distance, and largely enhanced heat exchange. The recent two decades have witnessed the rapid advances of microfluidic technologies in various fields such as biotechnology, analytical science, and diagnostics, as well as physical, chemical, and biological research. With the advances of nanomaterial and soft matter research, there have been some reports of the advantages discovered during attempts to synthesize these materials on microfluidic chips. As the formation of nanomaterials and soft matters is sensitive to the environment where the building blocks are fed, the unique physical environment of microfluidics and the effectiveness in coupling with other force fields open up a lot of possibilities to form new products as compared to conventional bulk synthesis.

This perspective summarizes the recent progresses in producing novel functional materials using microfluidics, such as generating particles with narrow and controlled size distribution, structured hybrid materials, and particles with new structures, completing reactions with quicker rate and new reaction route, and enabling more effective and efficient control on reactions. This promise is originated from some inherent characters of microfluidic systems, such as fast and precisely controllable mass and heat transfer, largely enhanced interface effect, confinement effect, templating effect, low-Reynolds number flow behavior, flexibility in coupling with different types of actuators and physical fields, versatile and effective control of highly localized environment, and convenience in integrating different functional modules into an automatic system. Quite a large portion of these functionalities are still underexplored, leaving large room to new possibilities. Finally, the trend of future development in this field is also discussed, such as the recovery of products and channel clogging during production.

While the microfluidic synthesis of some specific types of products have been discussed elsewhere, the present perspective is organized in the angle of different enabling powers of microfluidic synthesis originated from the unique physical environment. We structured the whole perspective into five sections, each discussing one major enabling power, while within each section we still divide the discussion by the different physical characters employed for special functions in the synthesis. We anticipate this unique angle of organization not only serves for quickly summarizing the major means employed in microfluidic synthesis, but also provides useful information to readers generally beyond the field of microfluidics about how and why microfluidics can provide new possibilities in synthesis, which may inspire their interest in trying out on their own reactions on chip. With the potential in conveniently scaling up the microfluidic synthesis, we anticipate a wave of rapid advance in microfluidic-based technologies for creating new functional materials.