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Title: Effect of Corona Block Length on the Structure and Chain Exchange Kinetics of Block Copolymer Micelles

Abstract

The effect of corona block length on micelle structure and molecular chain exchange kinetics has been investigated for a series of dilute poly(styrene)-b-poly(ethylene-alt-propylene) (SEP) diblock copolymer micelles with constant PS core block length ($$\langle$$Ncore$$\rangle$$ ≈ 255) but different PEP corona block lengths (($$\langle$$Ncorona$$\rangle$$ = 256–2080), using a combination of dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and time-resolved small-angle neutron scattering (TR-SANS). Smaller core radii and aggregation numbers, but significantly thicker corona layers (proportional to Ncorona0.7), were observed with increasing corona block length. Furthermore, 2 orders of magnitude more rapid chain exchange was observed in SEP micelles with the longest corona block compared to the shortest. This effect is attributed to the entropic gain arising from the relief of corona chain stretching upon chain expulsion. We further extend a previous theoretical model by explicitly including a corona term associated with the entropy change in the chain exchange process, which successfully explains the influence of the corona blocks on chain exchange. Our results are in excellent agreement with simulation results of Li and Dormidontova but are apparently contradictory with Halperin and Alexander’s theory for hairy micelles and with experimental observations in two other systems that the exchange kinetics slow downmore » with increasing corona block length. These discrepancies reveal unanticipated complexity regarding the role of the corona block in chain exchange.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Univ. of Minnesota, Minneapolis, MN (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1455243
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 51; Journal Issue: 10; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
ENGLISH
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Activation energy; Micelles; Copolymers; Solvents; Kinetics

Citation Formats

Wang, En, Lu, Jie, Bates, Frank S., and Lodge, Timothy P.. Effect of Corona Block Length on the Structure and Chain Exchange Kinetics of Block Copolymer Micelles. United States: N. p., 2018. Web. doi:10.1021/acs.macromol.7b02732.
Wang, En, Lu, Jie, Bates, Frank S., & Lodge, Timothy P.. Effect of Corona Block Length on the Structure and Chain Exchange Kinetics of Block Copolymer Micelles. United States. https://doi.org/10.1021/acs.macromol.7b02732
Wang, En, Lu, Jie, Bates, Frank S., and Lodge, Timothy P.. 2018. "Effect of Corona Block Length on the Structure and Chain Exchange Kinetics of Block Copolymer Micelles". United States. https://doi.org/10.1021/acs.macromol.7b02732. https://www.osti.gov/servlets/purl/1455243.
@article{osti_1455243,
title = {Effect of Corona Block Length on the Structure and Chain Exchange Kinetics of Block Copolymer Micelles},
author = {Wang, En and Lu, Jie and Bates, Frank S. and Lodge, Timothy P.},
abstractNote = {The effect of corona block length on micelle structure and molecular chain exchange kinetics has been investigated for a series of dilute poly(styrene)-b-poly(ethylene-alt-propylene) (SEP) diblock copolymer micelles with constant PS core block length ($\langle$Ncore$\rangle$ ≈ 255) but different PEP corona block lengths (($\langle$Ncorona$\rangle$ = 256–2080), using a combination of dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and time-resolved small-angle neutron scattering (TR-SANS). Smaller core radii and aggregation numbers, but significantly thicker corona layers (proportional to Ncorona0.7), were observed with increasing corona block length. Furthermore, 2 orders of magnitude more rapid chain exchange was observed in SEP micelles with the longest corona block compared to the shortest. This effect is attributed to the entropic gain arising from the relief of corona chain stretching upon chain expulsion. We further extend a previous theoretical model by explicitly including a corona term associated with the entropy change in the chain exchange process, which successfully explains the influence of the corona blocks on chain exchange. Our results are in excellent agreement with simulation results of Li and Dormidontova but are apparently contradictory with Halperin and Alexander’s theory for hairy micelles and with experimental observations in two other systems that the exchange kinetics slow down with increasing corona block length. These discrepancies reveal unanticipated complexity regarding the role of the corona block in chain exchange.},
doi = {10.1021/acs.macromol.7b02732},
url = {https://www.osti.gov/biblio/1455243}, journal = {Macromolecules},
issn = {0024-9297},
number = 10,
volume = 51,
place = {United States},
year = {2018},
month = {5}
}

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Works referencing / citing this record:

Interplay of Solvation and Size Effects Induced by the Counterions in Ionic Block Copolymers on the Basis of Hofmeister Series
journal, January 2019