Microporous Polymer Particles via Phase Inversion in Microfluidics: Impact of Nonsolvent Quality

Abstract

We investigate the impact of ternary phase behavior on the microstructure of porous polymer particles produced by solvent extraction of polymer solution droplets by a nonsolvent. Microfluidic devices fabricated by frontal photopolymerization are employed to produce monodisperse polymer (P)/solvent (S) droplets suspended in a carrier (C) phase before inducing solvent extraction by precipitation in a nonsolvent (NS) bath. Model systems of sodium poly(styrenesulfonate) (P), water (S), hexadecane (C), and either methyl ethyl ketone (MEK) or ethyl acetate (EA) as NS are selected. Extraction across the liquid-liquid interface results in a decrease in the droplet radius and also an ingress of nonsolvent, leading to droplet phase demixing and coarsening. As the concentration of the polymer-rich phase increases, droplet shrinkage and solvent exchange slow down and eventually cease, resulting in microporous polymer particles (of radius ≃50-200 μm) with a smooth surface. The internal structure of these capsules, with pore sizes of ≃1-100 μm, is found to be controlled by polymer solution thermodynamics and the extraction pathway. The ternary phase diagrams are measured by turbidimetry, and the kinetics of phase separation is estimated by stopped-flow small-angle neutron scattering. The higher solubility of water in MEK results in faster particle-formation kinetics than in EA. Surprisingly, however, the lower polymer miscibility with EA/water results in a deeper quench inside the phase boundary and small phase sizes, thus yielding particles with small pores (of narrow distribution). The effects of droplet size, polymer content, and nonsolvent quality provide comprehensive insight into porous particle and capsule formation by phase inversion, with a range of practical applications.

Macroporous materials: microfluidic fabrication, functionalization and applications

“…Unlike the works of Pelzbauer et al 13 and Dubinsky et al 17 in which porogens were used to obtain closed macroporous particles, more recently, Udoh et al 141 employed a microfluidic solvent extraction approach to prepare ''skin'' polymer particles ( Fig. 7).…”

Microfluidic Devices in Fabricating Nano or Micromaterials for Biomedical Applications

“…Yen et al obtained long‐time‐exposure images for the cooled outlet region of the gas–liquid segmented flow device operating under continuous UV excitation, which allowed real‐time monitoring of the quenching effect during the synthesis of QDs . Apart from real‐time spectroscopic and microscopic monitoring, new monitoring devices have also been adopted for better monitoring of the reaction process including small‐angel neutron scattering (SANS), FTIR, and X‐ray absorption (XAS) …”

Synthesis of spike‐ball‐like polystyrene/poly(methyl methacrylate) composite particles via seeded polymerization

“…9 This has made fine-tuned production methods indispensable for advanced materials chemistry and processes. [10][11][12][13] Diverse morphologies have been developed using several methods including film and particle stretching, [14][15][16] micro-molding, 17 microfluidics [18][19][20] and synthetic methods such as the usual polymerization methods 12,21,22 and their seeded counterparts. [23][24][25][26][27][28][29][30] Various morphologies containing lobes on their surfaces have been presented with no success in the production of lobes with a high aspect ratio.…”