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Title: Strong stretching theory for pH-responsive polyelectrolyte brushes in large salt concentrations

Abstract

Here, we develop a theory for describing the thermodynamics, configuration, and electrostatics of strongly-stretched, pH-responsive polyelectrolyte (PE) brushes in the presence of large salt concentrations. The aim of the paper, therefore, is to study the properties of a PE brush in a salt concentration regime (namely, large concentrations of several molars) that has been hitherto unexplored theoretically in the context of PE brushes but can be routinely encountered in molecular scale simulations of the problem. The brushes are modelled using our recently developed augmented Strong Stretching Theory (SST), while the effect of the presence of the large salt concentration is accounted for by including the contributions of three different types of non-Poisson–Boltzmann (non-PB) effects to the free energy description of the PE brush induced electric double layer (EDL). These non-PB effects are ionic non-mean-field ion–ion correlations, solvent polarization, and the finite size effect of the ions and water dipoles. We study the individual influences of these different effects and show that the ion–ion correlations and solvent polarization effect reduce the brush height which consequently enhances the monomer density and leads to an electrostatic potential distribution of the brush induced EDL that has a larger magnitude at near-wall locations and becomesmore » zero at shorter distances from the wall. The finite size effect, on the other hand, increases the brush height and therefore, weakens the monomer density and leads to a smaller near-wall magnitude of the EDL potential that becomes zero at larger distances from the wall. In time, we consider the impact of all the three non-PB effects simultaneously and show that the ion–ion correlations and solvent polarization effect dominate the size effects and dictate the overall brush configuration and the EDL electrostatics. We also point out that the influence of all the three non-PB effects becomes the largest for a larger salt concentration and a smaller bulk pH. Finally, we compare our theoretical predictions with those obtained from our recently developed all-atom MD simulation model and obtain an excellent match.« less

Authors:
 [1];  [1];  [1]; ORCiD logo [1]
  1. Univ. of Maryland, College Park, MD (United States). Dept. of Mechanical Engineering
Publication Date:
Research Org.:
Univ. of Maryland, College Park, MD (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1633039
Alternate Identifier(s):
OSTI ID: 1632229
Grant/Contract Number:  
SC0017741
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP
Additional Journal Information:
Journal Volume: 22; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Etha, Sai Ankit, Sivasankar, Vishal Sankar, Sachar, Harnoor Singh, and Das, Siddhartha. Strong stretching theory for pH-responsive polyelectrolyte brushes in large salt concentrations. United States: N. p., 2020. Web. doi:10.1039/d0cp02099k.
Etha, Sai Ankit, Sivasankar, Vishal Sankar, Sachar, Harnoor Singh, & Das, Siddhartha. Strong stretching theory for pH-responsive polyelectrolyte brushes in large salt concentrations. United States. https://doi.org/10.1039/d0cp02099k
Etha, Sai Ankit, Sivasankar, Vishal Sankar, Sachar, Harnoor Singh, and Das, Siddhartha. 2020. "Strong stretching theory for pH-responsive polyelectrolyte brushes in large salt concentrations". United States. https://doi.org/10.1039/d0cp02099k. https://www.osti.gov/servlets/purl/1633039.
@article{osti_1633039,
title = {Strong stretching theory for pH-responsive polyelectrolyte brushes in large salt concentrations},
author = {Etha, Sai Ankit and Sivasankar, Vishal Sankar and Sachar, Harnoor Singh and Das, Siddhartha},
abstractNote = {Here, we develop a theory for describing the thermodynamics, configuration, and electrostatics of strongly-stretched, pH-responsive polyelectrolyte (PE) brushes in the presence of large salt concentrations. The aim of the paper, therefore, is to study the properties of a PE brush in a salt concentration regime (namely, large concentrations of several molars) that has been hitherto unexplored theoretically in the context of PE brushes but can be routinely encountered in molecular scale simulations of the problem. The brushes are modelled using our recently developed augmented Strong Stretching Theory (SST), while the effect of the presence of the large salt concentration is accounted for by including the contributions of three different types of non-Poisson–Boltzmann (non-PB) effects to the free energy description of the PE brush induced electric double layer (EDL). These non-PB effects are ionic non-mean-field ion–ion correlations, solvent polarization, and the finite size effect of the ions and water dipoles. We study the individual influences of these different effects and show that the ion–ion correlations and solvent polarization effect reduce the brush height which consequently enhances the monomer density and leads to an electrostatic potential distribution of the brush induced EDL that has a larger magnitude at near-wall locations and becomes zero at shorter distances from the wall. The finite size effect, on the other hand, increases the brush height and therefore, weakens the monomer density and leads to a smaller near-wall magnitude of the EDL potential that becomes zero at larger distances from the wall. In time, we consider the impact of all the three non-PB effects simultaneously and show that the ion–ion correlations and solvent polarization effect dominate the size effects and dictate the overall brush configuration and the EDL electrostatics. We also point out that the influence of all the three non-PB effects becomes the largest for a larger salt concentration and a smaller bulk pH. Finally, we compare our theoretical predictions with those obtained from our recently developed all-atom MD simulation model and obtain an excellent match.},
doi = {10.1039/d0cp02099k},
url = {https://www.osti.gov/biblio/1633039}, journal = {Physical Chemistry Chemical Physics. PCCP},
issn = {1463-9076},
number = ,
volume = 22,
place = {United States},
year = {Mon May 11 00:00:00 EDT 2020},
month = {Mon May 11 00:00:00 EDT 2020}
}

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