Microfluidic solvent extraction of poly (vinyl alcohol) droplets: effect of polymer structure on particle and capsule formation
File(s)
Published version
Author(s)
Sharratt, William
Brooker, Anju
Robles, Eric
Cabral, JP
Type
Journal Article
Abstract
We investigate the formation of poly(vinyl alcohol) microparticles by the selective extraction of aqueous polymer solution droplets, templated by microfluidics and subsequently immersed in a non-solvent bath. The role of polymer molecular mass (18–105 kg mol−1), degree of hydrolysis (88–99%) and thus solubility, and initial solution concentration (0.01–10% w/w) are quantified. Monodisperse droplets with radii ranging from 50 to 500 μm were produced at a flow-focusing junction with carrier phase hexadecane and extracted into ethyl acetate. Solvent exchange and extraction result in droplet shrinkage, demixing, coarsening and phase-inversion, yielding polymer microparticles with well-defined dimensions and internal microstructure. Polymer concentration, varied from below the overlap concentration c* to above the concentrated crossover c**, as estimated by viscosity measurements, was found to have the largest impact on the final particle size and extraction timescale, while polymer mass and hydrolysis played a secondary role. These results are consistent with the observation that the average polymer concentration upon solidification greatly exceeds c**, and that the internal microparticle porosity is largely unchanged. However, reducing the initial polymer concentration to well below c* (approximately 100×) and increasing droplet size yields thin-walled (100's of nm) capsules which controllably crumple upon extraction. The symmetry of the process can be readily broken by imposing extraction conditions at an impermeable surface, yielding large, buckled, cavity morphologies. Based on these results, we establish robust design criteria for polymer capsules and particles, demonstrated here for poly(vinyl alcohol), with well-defined shape, dimensions and internal microstructure.
Date Issued
2018-06-14
Date Acceptance
2018-03-02
Citation
Soft Matter, 2018, 14, pp.4453-4463
ISSN
1744-683X
Publisher
Royal Society of Chemistry
Start Page
4453
End Page
4463
Journal / Book Title
Soft Matter
Volume
14
Copyright Statement
© The Royal Society of Chemistry 2018. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (https://creativecommons.org/licenses/by/3.0/)
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
iCASE Voucher Number: 16000164 with Procter & Gamble
Subjects
03 Chemical Sciences
09 Engineering
02 Physical Sciences
Chemical Physics
Publication Status
Published
Article Number
Manuscript ID: SM-ART-12-2017-002488.R1
Date Publish Online
2018-04-26