Microfluidic devices have recently emerged as promising tools for the synthesis of polymer particles. Over conventional processes, microfluidic-assisted processes allow the production of polymer particles with an improved control over their sizes, size distributions, morphologies, and compositions. In this paper, the most common microfluidic devices are reviewed. Both projection photolithography and emulsification processes are reported for the continuous flow synthesis of polymer particles from a stream of polymerizable liquids. For the latter process, two distinct categories of microfluidic devices have been identified: microchannel-based and capillary-based microsystems. For each category, the existing geometries are described and the different emulsification methods including the coflowing, cross-flowing, or flow-focusing of the continuous and dispersed phases are commented upon. Finally, for each microsystem the various polymer particles achieved in such devices including, but not restricted to, janus, core-shell, or porous particles and capsules are reported.

An easy assembling-disassembling co-axial capillaries microfluidic device was built up for the production of double droplets. Uniform polymer core-polymer shell particles were synthesized by polymerizing the two immiscible monomer phases composing the double droplet. Thus poly(acrylamide) core-poly(tri(propylene glycol) diacrylate) shell particles with controlled core diameter and shell thickness were simply obtained by adjusting operating parameters. An empirical law was extracted from experiments to predict core and shell sizes. Additionally uniform and predictable non-spherical polymer objects were also prepared without adding shape-formation procedures in the experimental device. An empirical equation for describing the lengths of rod-like polymer particles is also presented.

Capillary-based flow-focusing and co-flow microsystems were developed to produce sphere-like polymer microparticles of adjustable sizes in the range of 50 to 600 μm with a narrow size distribution (CV < 5%) and different morphologies (core-shell, janus, and capsules). Rod-like particles whose length was conveniently adjusted between 400 μm and few millimeters were also produced using the same microsystems. Influence of operating conditions (flow rate of the different fluid, microsystem characteristic dimensions, and design) as well as material parameters (viscosity of the different fluids and surface tension) was investigated. Empirical relationships were thus derived from experimental data to predict the microparticle's overall size, shell thickness, or rods length. Besides morphology, microparticles with various compositions were synthesized and their potential applications highlighted: drug-loaded microparticles for new drug delivery strategies, composed inorganic-organic multiscale microparticles for sensorics, and liquid crystalline elastomer microparticles showing an anisotropic reversible shape change upon temperature for thermal actuators or artificial muscles.

Tri(propylene glycol) diacrylate (TPGDA) was found to be an excellent monomer for the stabilization and dispersion of inorganic nanoparticles. Uniform nano-Au/poly(TPGDA) and nano-ZnO/poly(TPGDA) composite microbeads were synthesized in situ using a designed axisymmetric capillary-based flow-focusing microfluidic device without any additional surfactant or coupling agent. Using the designed mixing-enhanced microfluidic device, homogeneous nano-inorganic/polymer composites with a high content of nanoparticles were obtained. Morphologies of the composites were characterized by SEM, TEM, surface microscopy, dark-field microscopy and internal fluorescence.