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Salt-doped block copolymers: ion distribution, domain spacing and effective χ parameter

Nakamura, Issei and Wang, Zhen-Gang (2012) Salt-doped block copolymers: ion distribution, domain spacing and effective χ parameter. Soft Matter, 8 (36). pp. 9356-9367. ISSN 1744-6848. doi:10.1039/c2sm25606a.

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We develop a self-consistent field theory for salt-doped diblock copolymers, such as polyethylene oxide (PEO)–polystyrene with added lithium salts. We account for the inhomogeneous distribution of Li+ ions bound to the ion-dissolving block, the preferential solvation energy of anions in the different block domains, the translational entropy of anions, the ion-pair equilibrium between polymer-bound Li+ and anion, and changes in the χ parameter due to the bound ions. We show that the preferential solvation energy of anions provides a large driving force for microphase separation. Our theory is able to explain many features observed in experiments, particularly the systematic dependence in the effective χ-parameter on the radius of the anions, the observed linear dependence in the effective χ on salt concentration, and increase in the domain spacing of the lamellar phase due to the addition of lithium salts. We also examine the relationship between two definitions of the effective χ parameter, one based on the domain spacing of the ordered phase and the other based on the structure factor in the disordered phase. We argue that the latter is a more fundamental measure of the effective interaction between the two blocks. We show that the ion distribution and the electrostatic potential profile depend strongly on the dielectric contrast between the two blocks and on the ability of the Li+ to redistribute along the backbone of the ion-dissolving block.

Item Type:Article
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URLURL TypeDescription DOIArticle
Nakamura, Issei0000-0002-2701-6913
Wang, Zhen-Gang0000-0002-3361-6114
Additional Information:© 2012 The Royal Society of Chemistry. Received 16th March 2012, Accepted 28th May 2012. This research has been supported by the National Science Foundation, Grant Nos. CBET-0965812 and CHE-1040558.
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Issue or Number:36
Record Number:CaltechAUTHORS:20121001-151047732
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34605
Deposited By: Tony Diaz
Deposited On:01 Oct 2012 22:22
Last Modified:09 Nov 2021 23:09

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