Cornel, E.J., O'Hora, P.S., Smith, T. et al. (3 more authors) (2020) SAXS studies of the thermally-induced fusion of diblock copolymer spheres : formation of hybrid nanoparticles of intermediate size and shape. Chemical Science, 11 (17). pp. 4312-4321. ISSN 2041-6520
Abstract
Dilute dispersions of poly(lauryl methacrylate)–poly(benzyl methacrylate) (PLMA–PBzMA) diblock copolymer spheres (a.k.a. micelles) of differing mean particle diameter were mixed and thermally annealed at 150 °C to produce spherical nanoparticles of intermediate size. The two initial dispersions were prepared via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate in n-dodecane at 90 °C. Systematic variation of the mean degree of polymerization of the core-forming PBzMA block enabled control over the mean particle diameter: small-angle X-ray scattering (SAXS) analysis indicated that PLMA39–PBzMA97 and PLMA39–PBzMA294 formed well-defined, non-interacting spheres at 25 °C with core diameters of 21 ± 2 nm and 48 ± 5 nm, respectively. When heated separately, both types of nanoparticles regained their original dimensions during a 25–150–25 °C thermal cycle. However, the cores of the smaller nanoparticles became appreciably solvated when annealed at 150 °C, whereas the larger nanoparticles remained virtually non-solvated at this temperature. Moreover, heating caused a significant reduction in mean aggregation number for the PLMA39–PBzMA97 nanoparticles, suggesting their partial dissociation at 150 °C. Binary mixtures of PLMA39–PBzMA97 and PLMA39–PBzMA294 nanoparticles were then studied over a wide range of compositions. For example, annealing a 1.0% w/w equivolume binary mixture led to the formation of a single population of spheres of intermediate mean diameter (36 ± 4 nm). Thus we hypothesize that the individual PLMA39–PBzMA97 chains interact with the larger PLMA39–PBzMA294 nanoparticles to form the hybrid nanoparticles. Time-resolved SAXS studies confirm that the evolution in copolymer morphology occurs on relatively short time scales (within 20 min at 150 °C) and involves weakly anisotropic intermediate species. Moreover, weakly anisotropic nanoparticles can be obtained as a final copolymer morphology over a restricted range of compositions (e.g. for PLMA39–PBzMA97 volume fractions of 0.20–0.35) when heating dilute dispersions of such binary nanoparticle mixtures up to 150 °C. A mechanism involving both chain expulsion/insertion and micelle fusion/fission is proposed to account for these unexpected observations.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020 The Authors. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. https://creativecommons.org/licenses/by/3.0/ |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > Department of Chemistry (Sheffield) |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 12 May 2020 10:23 |
Last Modified: | 12 May 2020 10:31 |
Status: | Published |
Publisher: | Royal Society of Chemistry (RSC) |
Refereed: | Yes |
Identification Number: | 10.1039/d0sc00569j |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:160590 |