TY - JOUR
T1 - Ionic Conductance of Polyelectrolyte-Modified Nanochannels
T2 - Nanoconfinement Effects on the Coupled Protonation Equilibria of Polyprotic Brushes
AU - Gilles, Facundo M.
AU - Tagliazucchi, Mario
AU - Azzaroni, Omar
AU - Szleifer, Igal
N1 - Funding Information:
F.M.G. acknowledges a doctoral scholarship from CONICET (Argentina). O.A. and M.T. are CONICET fellows. F.M.G. would like to thank R. Nap and G. Longo for stimulating discussions and G. Putzel for valuable comments and criticisms. This work was supported as part of the Center for Bio-Inspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under award no. DE-SC0000989. This research was supported in part through the computational resources and staff contributions provided by the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. O.A. acknowledges financial support from ANPCyT (PICT 2010-2554 and PICT-2013-0905), Consejo Nacional de Investigaciones Cient?ficas y Te?cnicas (CONICET) (PIP 11220130100370CO), Fundacio?n Petruzza, and the Austrian Institute of Technology GmbH (AIT-CONICET Partner Lab: "Exploratory Research for Advanced Technologies in Supramolecular Materials Science" - Exp. 4947/11, res. no. 3911).
PY - 2016/3/17
Y1 - 2016/3/17
N2 - A theoretical methodology is introduced to calculate the low-bias conductance, structure, and composition of long polyelectrolyte-modified nanochannels of arbitrary geometry. This methodology is applied to explore the coupling between acid-base equilibrium and geometry in cylindrical, conical, and trumpet-shaped nanochannels modified by end-grafted layers of poly(2-(methacryloyloxy)ethyl-phosphate) (PMEP), a diprotic polyacid. The ionic conductance and speciation curves (i.e., the fraction of deprotonated, monoprotonated, and diprotonated acid segments) for this system were predicted as a function of the solution pH. The apparent pKa's and widths of the transitions between the different acid-base states determined from the speciation curves depend on the diameter and shape of the nanochannel and the bulk salt concentration. In the limit of wide channels, the apparent pKa's and widths can be estimated by a simplified analytical model derived from the more general molecular theory. Both the general and the simplified theory predicts that, due to charge-regulation effects, the first acid-base transition (0/-1 transition) is wider than the second one (-1/-2), and both transitions are wider than the ideal one expected for an isolated acid-base group in the bulk. It is also shown that the inflection points of the conductance versus pH curves provide a very good estimation of the apparent pKa's of the polyelectrolyte for cylindrical channels, but the quality of the estimation decreases for noncylindrical geometries.
AB - A theoretical methodology is introduced to calculate the low-bias conductance, structure, and composition of long polyelectrolyte-modified nanochannels of arbitrary geometry. This methodology is applied to explore the coupling between acid-base equilibrium and geometry in cylindrical, conical, and trumpet-shaped nanochannels modified by end-grafted layers of poly(2-(methacryloyloxy)ethyl-phosphate) (PMEP), a diprotic polyacid. The ionic conductance and speciation curves (i.e., the fraction of deprotonated, monoprotonated, and diprotonated acid segments) for this system were predicted as a function of the solution pH. The apparent pKa's and widths of the transitions between the different acid-base states determined from the speciation curves depend on the diameter and shape of the nanochannel and the bulk salt concentration. In the limit of wide channels, the apparent pKa's and widths can be estimated by a simplified analytical model derived from the more general molecular theory. Both the general and the simplified theory predicts that, due to charge-regulation effects, the first acid-base transition (0/-1 transition) is wider than the second one (-1/-2), and both transitions are wider than the ideal one expected for an isolated acid-base group in the bulk. It is also shown that the inflection points of the conductance versus pH curves provide a very good estimation of the apparent pKa's of the polyelectrolyte for cylindrical channels, but the quality of the estimation decreases for noncylindrical geometries.
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U2 - 10.1021/acs.jpcc.5b11788
DO - 10.1021/acs.jpcc.5b11788
M3 - Article
AN - SCOPUS:84961163335
VL - 120
SP - 4789
EP - 4798
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
SN - 1932-7447
IS - 9
ER -