Abstract
Block copolymer micelles enable the formation of widely tunable self-assembled structures in liquid phases, with applications ranging from drug delivery to personal care products to nanoreactors. In order to understand fundamental aspects of micelle assembly and dynamics, the structural properties and solvent uptake of biocompatible poly(ethylene oxide-b-ϵ-caprolactone) (PEO-PCL) diblock copolymers in deuterated water (D2O)/tetrahydrofuran (THF-d8) mixtures were investigated with a combination of small-angle neutron scattering, nuclear magnetic resonance, and transmission electron microscopy. PEO-PCL block copolymers, of varying molecular weight yet constant block ratio, formed spherical micelles through a wide range of solvent compositions. Varying the solvent composition from 10 to 60 vol % THF-d8 in D2O/THF-d8 mixtures was a convenient means of varying the core-corona interfacial tension in the micelle system. An increase in THF-d8 content in the bulk solvent increased the solvent uptake within the micelle core, which was comparable for the two series, irrespective of the polymer molecular weight. Whereas the smaller molecular weight micelle series exhibited a decrease in aggregation number with increasing THF-d8 content in the bulk solvent, as anticipated due to changes in the core-corona interfacial tension, the aggregation number of the larger molecular weight series was surprisingly invariant with bulk solvent composition. Differences in the dependencies of the micelle size parameters (core radius and overall micelle radius) on the solvent composition originated from the differing trends in aggregation number for the two micelle series. Incorporation of the known unimer content determined from NMR (described in the companion paper), and directly accounting for impacts of solvent swelling of the micelle core on the neutron scattering length density of the core, allowed refinement of and increased confidence in extracted micelle parameters. In summary, the two micelle series showed similar solvent uptake that was independent of the polymer molecular weight yet significantly different dependencies of their aggregation number and size parameters on the solvent composition.
| Original language | English |
|---|---|
| Pages (from-to) | 4322-4334 |
| Number of pages | 13 |
| Journal | Macromolecules |
| Volume | 50 |
| Issue number | 11 |
| DOIs | |
| State | Published - Jun 13 2017 |
Funding
We are grateful to Paul Butler and Thomas Epps, III, for insight regarding SANS data fitting. This work benefitted from SasView software, originally developed by the DANSE project under NSF Award DMR-0520547, and can be found online at http://www.sasview.org. A portion of this research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Certain trade names and company products are identified to foster understanding. In no case does suchidentification imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the products are necessarily the best for the purpose. We thank Jeffrey Rimer for access to the DLS instrument and Matthew Oleksiak, Mohammad Safari, Ye Li, Ryan Poling- Skutvik, and Maria Vorontsova for training and discussions regarding DLS analysis. We appreciate the assistance of Charles Anderson for access and training in the University of Houston Department of Chemistry Nuclear Magnetic Resonance Facility. Missy Hazen is gratefully acknowledged for technical support with cryo-TEM experiments. We thank Vivek Yadav and David Truong for assistance with contact angle measurements and spin coating and Gila Stein for access to the contact angle-measuring instrument and spin coater. T.J.C., A.S., K.M.L., S.W., and M.L.R. gratefully acknowledge support from the National Science Foundation under Grants CBET- 1437831 and DMR-1351788 as well as support from the University of Houston. E.G.K. was partially supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health (NIH) grant, P20GM103541, to the University of Delaware. S.V.K. and E.D.G. acknowledge funding support from the National Science Foundation under Grants DMR- 1056199 and DMR-1609417. B.E.K. and L.A.M. acknowledge funding support from the National Science Foundation under Grant CBET-1437767.
| Funders | Funder number |
|---|---|
| University of Houston Department of Chemistry Nuclear Magnetic Resonance Facility | |
| National Science Foundation | 1351788, 1437767, DMR-1351788, CBET- 1437831, DMR-0520547 |
| National Institutes of Health | P20GM103541, DMR-1609417, CBET-1437767, DMR- 1056199 |
| National Institute of General Medical Sciences | |
| National Institute of Standards and Technology | |
| Office of Science | |
| Oak Ridge National Laboratory | |
| University of Houston |