Simulations of the Titration of Linear Polyelectrolytes with Explicit Simple Ions:  Comparisons with Screened Coulomb Models and Experiments

Abstract

Monte Carlo simulations of linear, weak polyacids and explicit simple ions have been performed in a spherical cell model to study the shift in the apparent dissociation constant. The simulations are performed in a canonical ensemble with the apparent dissociation constant calculated in a procedure based on Widom's particle-insertion method. The effects of model parameters are discussed, for example, the influence of various distances of closest approach, and the results are compared to experiments as well as simulations with effective pair-potentials between monomers, both the screened Coulomb potential and an extended version that takes into account a distance of closest approach between monomers and simple ions. Results of the latter potential are also compared to the experimental data, which are from poly(acrylic acid), poly-D,L-glutamic acid and carboxymethyl cellulose.

Simulation of weak polyelectrolytes: a comparison between the constant pH and the reaction ensemble method

“…A negative prefactor defines a deprotonation reaction (diss) and a positive prefactor, vice versa assigns a protonation reaction (ass). Moreover, it has to be noted that the proposal probability for a protonation or deprotonation reaction in the constant pH method is asymmetric [11,30,31,15,16,17,14,18]. This can be shown by comparing the proposal probability for a deprotonation reaction which reads g(diss|ass) = NHA/N0, with the proposal probability for a protonation reaction defined as g(ass|diss) = N A − /N0, which implies g(ass|diss) = g(diss|ass).…”

“…The constant pH method [11] implements a constant and global pH value as an input parameter which balances the probability of protonation and deprotonation reactions. The method was originally developed to simulate linear polyelectrolytes in presence and absence of excess salt and counterions [11,12,13,14] and reveals a good agreement with analytical results [15]. More effort was additionally spent on the study of different solvent conditions and their influence on polyelectrolyte conformations [16,17] and the properties of polyampholytes [18,5].…”

Osmotic pressure in polyelectrolyte solutions: cell-model and bulk simulations

“…Previously, the cell model has given a good agreement with the titration curve of polyacrylic acid using a bond length of 4.5 Å. 44 This gives a larger osmotic coefficient. Thus, selecting the smaller bond length improves the agreement with experiments here at the cost of being inconsistent.…”

The many facets of polyelectrolytes and oppositely charged macroions complex formation

“…It should be noted here that most of the computer simulations of PE complexation considered strong polyelectrolytes, although titrating or weak polyelectrolytes, which are an important class of PEs, were mainly studied by computer simulations for the isolated case [46][47][48]. The complex formation between macroions and a weak anionic PE was recently systematically investigated [34][35][36] pointing out the importance of several competing effects on the PE-macroion complex structure and the influence of the macroion(s) on the PE titration curve as shown in Fig.…”