Abstract
Materials science is a fast-evolving area that aims to uncover functional materials with ever more sophisticated properties and functions. For this to happen, new methodologies for materials synthesis, optimization, and preparation are desired. In this context, microfluidic technologies have emerged as a key enabling tool for a low-cost and fast prototyping of materials. Their ability to screen multiple reaction conditions rapidly with a small amount of reagent, together with their unique physico-chemical characteristics, have made microfluidic devices a cornerstone technology in this research field. Among the different microfluidic approaches to materials synthesis, the main contenders can be classified in two categories: continuous-flow and segmented-flow microfluidic devices. These two families of devices present very distinct characteristics, but they are often pooled together in general discussions about the field with seemingly little awareness of the major divide between them. In this perspective, we outline the parallel evolution of those two sub-fields by highlighting the key differences between both approaches, via a discussion of their main achievements. We show how continuous-flow microfluidic approaches, mimicking nature, provide very finely-tuned chemical gradients that yield highly-controlled reaction–diffusion (RD) areas, while segmented-flow microfluidic systems provide, on the contrary, very fast homogenization methods, and therefore well-defined super-saturation regimes inside arrays of micro-droplets that can be manipulated and controlled at the milliseconds scale. Those two classes of microfluidic reactors thus provide unique and complementary advantages over classical batch synthesis, with a drive towards the rational synthesis of out-of-equilibrium states for the former, and the preparation of high-quality and complex nanoparticles with narrow size distributions for the latter.
Highlights
In the last two decades, there has been a growing interest in using microfluidic devices for the synthesis of materials, the main reason being that microfluidic conditions offer significant advantages over macroscopic laboratory settings: reduced reactant consumption, high surface area to volume ratios, and improved control over mass and heat transfer are some of their unique assets [1,2]
Among all of the different microfluidic approaches employed for materials synthesis [9], we will focus our attention on continuous- and segmented-flow microfluidic devices used in the synthesis of crystalline materials
We will show that continuous and segmented-flow microfluidic microfluidic have emerged as landmark technologies for capture both (i) the captureand of kinetic and devices havedevices emerged as landmark technologies for both (i) the of kinetic metastable metastable states, and (ii)and theproduction discovery ofand production of materials states, and (ii) the discovery materials with controlled sizeswith and controlled sizes and shapes, opening new vistas to the materialization of novel shapes, opening new vistas to the materialization of novel structure–property structure–property correlations in existing artificial compounds
Summary
In the last two decades, there has been a growing interest in using microfluidic devices for the synthesis of materials, the main reason being that microfluidic conditions offer significant advantages over macroscopic laboratory settings: reduced reactant consumption, high surface area to volume ratios, and improved control over mass and heat transfer are some of their unique assets [1,2]. Among all of the different microfluidic approaches employed for materials synthesis [9], we will focus our attention on continuous- and segmented-flow microfluidic devices used in the synthesis of crystalline materials While those two configurations may not seem radically different at first glance—for instance, both situations correspond to very low Reynolds (Re) numbers and highly laminar flow conditions—they rely on fundamentally different processes for combining the reagents. Continuous-flow microfluidic devices are experiencing relentless growth, because kinetic versus thermodynamic control in the formation of reaction products can be accomplished; a result that can potentially lead to new unprecedented materials and functions [19].
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