Flow-directed solution self-assembly of block copolymers in microfluidic devices
| dc.contributor.author | Wang, Chih-Wei | |
| dc.contributor.supervisor | Moffitt, Matthew | |
| dc.contributor.supervisor | Sinton, David A. | |
| dc.date.accessioned | 2012-05-07T21:09:40Z | |
| dc.date.available | 2013-04-21T11:22:03Z | |
| dc.date.copyright | 2012 | en_US |
| dc.date.issued | 2012-05-07 | |
| dc.degree.department | Department of Chemistry | |
| dc.degree.level | Doctor of Philosophy Ph.D. | en_US |
| dc.description.abstract | The self-assembly of polystyrene-stabilized cadmium sulfide nanoparticles (PS-CdS) with amphiphilic stabilizing chains of polystyrene-block-poly(acrylic acid) (PS-b-PAA) into colloidal quantum dot compound micelles (QDCMs) is studied on two-phase gas-liquid segmented microfluidic reactors. The resulting particle sizes are found to arise from the interplay of shear-induced coalescence and particle breakup, depending on a combination of chemical and flow conditions. Variation of water content, gas-to-liquid ratio, and total flow rate, enable control of QDCM sizes in the range of 140 – 40 nm. The flow-variable shear effect on similar microfluidic reactors is then applied to direct the solution self-assembly of a PS-b-PAA block copolymer into various micelle morphologies. The difference between off-chip and on-chip morphologies under identical chemical conditions is explained by a mechanism of shear-induced coalescence enabled by strong and localized on-chip shear fields, followed by intraparticle chain rearrangements to minimize local free energies. Time-dependent studies of these nanostructures reveal that on-chip kinetic structures will relax to global equilibrium given sufficient time off-chip. Further investigations into the effect of chemical variables on on-chip shear-induced morphologies reveal a combination of thermodynamic and kinetic effects, opening avenues for morphology control via combined chemical (bottom-up) and shear (top-down) forces. An equilibrium phase diagram of off-chip micelle morphologies is constructed and used in conjunction with kinetic considerations to rationalize on-chip mechanisms and morphologies, including cylinders and vesicles, under different chemical conditions. Finally, we extend our strategy of two-phase microfluidic self-assembly of PS-b-PAA to the loading of fluorescent hydrophobic probes (pyrene and naphthalene) with different affinities for the PS core. The on-chip loading approach provides a fast alternate to the slow off-chip method, with implications for the potential development for point-of-care devices for drug loading. On-chip loading results indicate that loading efficiencies are dependent on water content and, to a lesser extent, on flow rate; the results also suggest that the on-chip morphologies of the PS-b-PAA micelles are an important factor in the loading efficiencies. | en_US |
| dc.description.scholarlevel | Graduate | en_US |
| dc.identifier.bibliographicCitation | Wang, C. W.; Oskooei, A.; Sinton, D.; Moffitt, M. G., Langmuir 2010, 26 (2), 716-723. | en_US |
| dc.identifier.bibliographicCitation | Wang, C. W.; Sinton, D.; Moffitt, M. G., J. Am. Chem. Soc. 2011, 133 (46), 18853-18864. | en_US |
| dc.identifier.uri | http://hdl.handle.net/1828/3984 | |
| dc.language.iso | en | en_US |
| dc.rights.temp | Available to the World Wide Web | en_US |
| dc.subject | self-assembly | en_US |
| dc.subject | polystyrene-block-poly(acrylic acid) (PS-b-PAA) | en_US |
| dc.subject | flow-variable shear effect | en_US |
| dc.subject | two-phase gas-liquid segmented microfluidic reactors | en_US |
| dc.subject | shear-induced coalescence and particle breakup | en_US |
| dc.subject | strong and localized on-chip shear fields | en_US |
| dc.subject | on-chip kinetic structures | en_US |
| dc.subject | global equilibrium | en_US |
| dc.subject | on-chip loading | en_US |
| dc.title | Flow-directed solution self-assembly of block copolymers in microfluidic devices | en_US |
| dc.type | Thesis | en_US |