title: A semi-grand canonical Monte Carlo simulation model for ion binding to ionizable surfaces: proton binding of carboxylated latex particles as a case study.
abstract: In this paper, we present a computer simulation study of the ion binding process at an ionizable surface using a semi-grand canonical Monte Carlo method that models the surface as a discrete distribution of charged and neutral functional groups in equilibrium with explicit ions modelled in the context of the primitive model. The parameters of the simulation model were tuned and checked by comparison with experimental titrations of carboxylated latex particles in the presence of different ionic strengths of monovalent ions. The titration of these particles was analysed by calculating the degree of dissociation of the latex functional groups vs. pH curves at different background salt concentrations. As the charge of the titrated surface changes during the simulation, a procedure to keep the electroneutrality of the system is required. Here, two approaches are used with the choice depending on the ion selected to maintain electroneutrality: counterion or coion procedures. We compare and discuss the difference between the procedures. The simulations also provided a microscopic description of the electrostatic double layer (EDL) structure as a function of pH and ionic strength. The results allow us to quantify the effect of the size of the background salt ions and of the surface functional groups on the degree of dissociation. The non-homogeneous structure of the EDL was revealed by plotting the counterion density profiles around charged and neutral surface functional groups.
authors.affiliation: Department of Physical Chemistry and Research Institute of Theoretical and Computational Chemistry (IQTCUB), University of Barcelona (UB), C/ Martí i Franquès, 1, E-08028 Barcelona, Spain. s.madurga@ub.edu
authors.forename: Sergio
authors.initials: S
authors.lastname: Madurga
authors.forename: Carlos
authors.initials: C
authors.lastname: Rey-Castro
authors.forename: Isabel
authors.initials: I
authors.lastname: Pastor
authors.forename: Eudald
authors.initials: E
authors.lastname: Vilaseca
authors.forename: Calin
authors.initials: C
authors.lastname: David
authors.forename: Josep Lluís
authors.initials: JL
authors.lastname: Garcés
authors.forename: Jaume
authors.initials: J
authors.lastname: Puy
authors.forename: Francesc
authors.initials: F
authors.lastname: Mas