Microfluidic platforms: a mainstream technology for the preparation of crystals

Abstract

Microfluidics is a multidisciplinary field of science based on the manipulation of fluids in sub-millimeter dimensions where the fundamental fluid physics changes dramatically when compared to macroscale fluid physical phenomena. Therefore, the conditions that microfluidic technologies offer are completely different from those of bulk set-ups, and thus they are very interesting for the study of crystallisation because diffusion, mixing and mass and heat transport are all finely controlled, and are easily modulated. This tutorial review is intended to give a broad and up-to-date overview of the distinct microfluidic approaches that have been employed so far for crystallisation studies for the uninitiated in these techniques. Main emphasis will be given to microfluidic platforms operating under continuous flow regimes, droplet-based methods, valve-based approaches, well-based methods, and digital microfluidics. This tutorial does not intend to give detailed methodology, but rather provides illustrative examples which capture the attention of the reader and allow them to appreciate the unique features that microfluidic technologies can offer towards the study of different crystallisation processes. Indeed, crystallisation studies of different types of crystalline matter including organic, inorganic and metal-organic materials are presented.

Microfluidic Synthesis Enables Dense and Uniform Loading of Surfactant‐Free PtSn Nanocrystals on Carbon Supports for Enhanced Ethanol Oxidation

“…[28][29][30][31][32][33][34] Additionally,m icrofluidic reactors can be operated under hydrothermal and solvothermal conditions,a nd limited mass diffusion in ac onfined volume leads to reaction kinetics significantly different from that of conventional bulk solution reactions.B oth attributes are expected to benefit the synthesis of uniform PtSn NPs on carbon supports,s uch as carbon black particles of XC-72. Once the reaction solution flows to the heating region, where the capillary tube is maintained at an elevated temperature,t he reaction solution in the tube can be quickly heated to the desired temperature within av ery short time [35] because of the rapid heat transfer in the thin capillary tube wall and the small volume of solution in the capillary tube.T he fast increase of reaction temperature to ac onstant value leads to ah igh reduction rate of H 2 PtCl 6 and SnCl 4 precursors,a chieving supersaturated concentrations of metal atoms in avery short reaction time.T he supersaturated Pt and Sn atoms nucleate on the surface of the carbon spheres in aw ell-dispersed fashion because heterogeneous nucleation is kinetically preferable compared to homogeneous nucleation. Theapplied pressure makes it possible to realize reactions at temperatures higher than the boiling point of the reaction solvent.…”

Controlled Crystallization of Sodium Chloride Nanocrystals in Microdrop­lets Produced by Electrospray from an Ultra‐Dilute Solution

“…[3] For the past few years, microfluidic technology has been attracting great interest due to its potential for precise manipulation of small quantities of fluids constrained in channels of dimensions from micrometers to millimeters. [4,5] In addition, localization and in situ characterization may be carried out during the experiment by spectroscopic techniques [6] or diffraction [7,8] studies. Zhu [9] obtained LaF 3 nanoparticles with a mean diameter of 4.5 nm and LaPO 4 nanorods with lengths of 60-70 nm and diameters of 10-15 nm in a microfluidic reactor by microwave irradiation.…”

Droplet Merging on a Lab-on-a-Chip Platform by Uniform Magnetic Fields

“…LoC applications of DMF require droplet manipulation in order to perform operations such as droplet merging, mixing, breakup, and sorting. Droplet manipulation on a LoC platform has been used for the synthesis of novel materials6 relevant to biosensing7, three-dimensional (3D) cell culture8, photonic crystals9, Janus structures10, anisotropic particles11, functional polymeric structures121314, controlled encapsulation for drug delivery15 and multidimensional optical barcoding16. Specifically, droplet merging and mixing on LoC platform has been used for a broad range of biomedical applications17 such as bioassays1819, biomaterials20, single cell analysis21, cell sorting2223, population transcriptomics24, disease detection25, and diagnostics26.…”