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Title: Structure of Polyelectrolyte Brushes in the Presence of Multivalent Counterions

Abstract

Polyelectrolyte brushes are of great importance to a wide range of fields, ranging from colloidal stabilization to responsive and tunable materials to lubrication. Here, we synthesized high-density polystyrenesulfonate (PSS) brushes using surface initiated atom transfer radical polymerization and performed neutron reflectivity (NR) and surface force measurements using a surface forces apparatus (SFA) to investigate the effect of monovalent Na +, divalent Ca 2+, Mg 2+, and Ba 2+, and trivalent Y 3+ counterions on the structure of the PSS brushes. NR and SFA results demonstrate that in monovalent salt solution the behavior of the PSS brushes agrees with scaling theory well, exhibiting two distinct regimes: the osmotic and salted brush regimes. Introducing trivalent Y 3+ cations causes an abrupt shrinkage of the PSS brush due to the uptake of Y 3+ counterions. The uptake of Y 3+ counterions and shrinkage of the brush are reversible upon increasing the concentration of monovalent salt. Divalent cations, Mg 2+, Ca 2+, and Ba 2+, while all significantly affecting the structure of PSS brushes, show strong ion specific effects that are related to the specific interactions between the divalent cations and the sulfonate groups. Our results demonstrate that the presence of multivalent counterions, evenmore » at relatively low concentrations, can strongly affect the structure of polyelectrolyte brushes. Finally, the results also highlight the importance of ion specificity to the structure of polyelectrolyte brushes in solution.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [1];  [1]
  1. Univ. of Chicago, IL (United States). Inst. for Molecular Engineering; Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division
  2. Univ. of Chicago, IL (United States). Inst. for Molecular Engineering
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research; Univ. of Akron, OH (United States). Dept. of Polymer Engineering
  4. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research
  5. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1352620
Grant/Contract Number:
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 49; Journal Issue: 15; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Yu, Jing, Mao, Jun, Yuan, Guangcui, Satija, Sushil, Jiang, Zhang, Chen, Wei, and Tirrell, Matthew. Structure of Polyelectrolyte Brushes in the Presence of Multivalent Counterions. United States: N. p., 2016. Web. doi:10.1021/acs.macromol.6b01064.
Yu, Jing, Mao, Jun, Yuan, Guangcui, Satija, Sushil, Jiang, Zhang, Chen, Wei, & Tirrell, Matthew. Structure of Polyelectrolyte Brushes in the Presence of Multivalent Counterions. United States. doi:10.1021/acs.macromol.6b01064.
Yu, Jing, Mao, Jun, Yuan, Guangcui, Satija, Sushil, Jiang, Zhang, Chen, Wei, and Tirrell, Matthew. 2016. "Structure of Polyelectrolyte Brushes in the Presence of Multivalent Counterions". United States. doi:10.1021/acs.macromol.6b01064. https://www.osti.gov/servlets/purl/1352620.
@article{osti_1352620,
title = {Structure of Polyelectrolyte Brushes in the Presence of Multivalent Counterions},
author = {Yu, Jing and Mao, Jun and Yuan, Guangcui and Satija, Sushil and Jiang, Zhang and Chen, Wei and Tirrell, Matthew},
abstractNote = {Polyelectrolyte brushes are of great importance to a wide range of fields, ranging from colloidal stabilization to responsive and tunable materials to lubrication. Here, we synthesized high-density polystyrenesulfonate (PSS) brushes using surface initiated atom transfer radical polymerization and performed neutron reflectivity (NR) and surface force measurements using a surface forces apparatus (SFA) to investigate the effect of monovalent Na+, divalent Ca2+, Mg2+, and Ba2+, and trivalent Y3+ counterions on the structure of the PSS brushes. NR and SFA results demonstrate that in monovalent salt solution the behavior of the PSS brushes agrees with scaling theory well, exhibiting two distinct regimes: the osmotic and salted brush regimes. Introducing trivalent Y3+ cations causes an abrupt shrinkage of the PSS brush due to the uptake of Y3+ counterions. The uptake of Y3+ counterions and shrinkage of the brush are reversible upon increasing the concentration of monovalent salt. Divalent cations, Mg2+, Ca2+, and Ba2+, while all significantly affecting the structure of PSS brushes, show strong ion specific effects that are related to the specific interactions between the divalent cations and the sulfonate groups. Our results demonstrate that the presence of multivalent counterions, even at relatively low concentrations, can strongly affect the structure of polyelectrolyte brushes. Finally, the results also highlight the importance of ion specificity to the structure of polyelectrolyte brushes in solution.},
doi = {10.1021/acs.macromol.6b01064},
journal = {Macromolecules},
number = 15,
volume = 49,
place = {United States},
year = 2016,
month = 7
}

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Cited by: 6works
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  • Surface tethered polyelectrolyte brushes are scientifically interesting and technologically relevant to many applications, ranging from colloidal stabilization to responsive and tunable materials to lubrication. Many applications operate in environments containing multi-valent ions, media in which our scientific understanding is not yet well-developed. In this paper, we synthesized high-density polystyrene sulfonate (PSS) brushes via surface initiated atom-transfer radical polymerization, and performed neutron reflectivity (NR) measurements to investigate and compare the effects of mono-valent Rb + and tri-valent Y 3+ counterions to the structure of the densely tethered PSS brushes. Our NR results show that in mono-valent RbNO 3 solution, the densemore » PSS brush retained its full thickness up to a salt concentration of 1 M, whereas it immediately collapsed upon adding 1.67 mM of tri-valent Y 3+. Increasing the concentration of Y 3+ beyond this level did not lead to any significant further structure change of the PSS brush. Finally, our findings demonstrate that the presence of multi-valent counterions can significantly alter the structure of polyelectrolyte brushes, in a manner different from mono-valent ions, which has implications for the functionality of the brushes.« less
  • We provide a theoretical model for the collapse of polyelectrolyte brushes in the presence of multivalent ions, focusing on the formation of lateral inhomogeneties in the collapsed state. Polyelectrolyte brushes are important in a variety of applications, including stabilizing colloidal particles and lubricating surfaces. Many uses rely on the extension of the densely grafted polymer chains from the surface in the extended brush morphology. In the presence Extended Brush of multivalent ions, brushes are significantly shorter than in monovalent ionic solutions, which greatly affects their properties. We base our theoretical analysis on an analogous collapse of polyelectrolyte brushes in amore » poor solvent, providing an energy balance representation for pinned micelles and cylindrical bundles. The equilibrium brush heights predicted for these structures are of a similar magnitude to those measured experimentally. The formation of lateral structures can open new avenues for stimuli-responsive applications that rely on nanoscale pattern formation on surfaces.« less
  • Here, coarse-grained molecular dynamics enhanced by free-energy sampling methods is used to examine the roles of solvophobicity and multivalent salts on polyelectrolyte brush collapse. Specifically, we demonstrate that while ostensibly similar, solvophobic collapsed brushes and multivalent-ion collapsed brushes exhibit distinct mechanistic and structural features. Notably, multivalent-induced heterogeneous brush collapse is observed under good solvent polymer backbone conditions, demonstrating that the mechanism of multivalent collapse is not contingent upon a solvophobic backbone. Umbrella sampling of the potential of mean-force (PMF) between two individual brush strands confirms this analysis, revealing starkly different PMFs under solvophobic and multivalent conditions, suggesting the role ofmore » multivalent “bridging” as the discriminating feature in trivalent collapse. Structurally, multivalent ions show a propensity for nucleating order within collapsed brushes, whereas poor-solvent collapsed brushes are more disordered; this difference is traced to the existence of a metastable PMF minimum for poor solvent conditions, and a global PMF minimum for trivalent systems, under experimentally relevant conditions.« less
  • We present a detailed analysis of the behavior of aqueous electrolyte-polyelectrolyte systems in contact with neutral and charged graphene substrates, based on an extensive molecular dynamics simulation effort. Our study involves aqueous systems comprising short-chains of lithium-polystyrene sulfonate with explicit atomistic description of water, the chain backbones, and their interactions with all species in solution as well as with the graphene surface. We place special emphasis on the behavior of the axial profiles of species concentrations, local electrostatic charge density, electric field and corresponding surface-charge screening to provide a full characterization of the inhomogeneous environment at the solid-liquid interface, i.e.,more » the electric double layer and the effect of the added salts (BaCl2 and LaCl3 ) on its structure. To complete the analysis, we assess the tendency toward ion pairing along planes parallel to the graphene surface and estimate, according to the axial distribution profiles, the strength of the adsorption of the polyelectrolyte, counterions, and other species in solution, in order to interpret the degree of surface-charge screening and the occurrence of surface-charge reversal. We present evidence of a recently reported new phenomenon of overcharging, and discuss the central role of the explicit description of the solvent on this occurrence. Moreover, to interpret the conformational behavior of the polyelectrolyte backbones we determine the axial profiles of the perpendicular and parallel components of the corresponding radius of gyration and end-to-end distance.« less