Tesis doctoral de JonÁ s Sala Viñas
In the last years, electrolyte solutions in confinement and in contact with hydrophobic and hydrophilic surfaces have received a lot of attention. Different problems in various fields such as biology, colloidal science or environmental sciences are benefiting from a better understanding of those systems. The study at a microscopic level by means of molecular dynamics (md) simulations of the structure, dynamic and dielectric properties of aqueous solutions in confinement conditions, provides valuable information that might allow to better understand, improve and control the relevant mechanisms that take place in those media. Explicitly taking into account polarization in the potentials that describe ions and molecules in the md simulations, have proven to be crucial in order to reproduce some experimentally observed phenomena such as the presence of anions at the interface between an aqueous solution and a hydrophobic surface. In parallel, lots of efforts are being directed towards obtaining classical potential models to be used in md simulations so that these systems are described more faithfully with lower computational costs. in the first part of the thesis, the necessary techniques and methods to explicitly incorporate polarization into our simulations are presented, using a formalism that allows to easily incorporate electrostatic damping functions that dampen short range intermolecular interactions. We have used this formalism to demonstrate that the use of damping in md simulations of a nacl solution, allows to assign realistic values for the polarizability of the ions and reproduce solvation anysotropy and dipole moment distributions for the cl ions obtained from ab initio simulations. as a preliminary step to the study of confined solutions, the effect of explicitly including polarization on the dielectric constant and conductivity for aqueous nacl solutions have been investigated. It have been found that the contribution form the cross terms between the current and the total dipole moment that appear in the computation of this properties, can become relevant when polarization is taken into account. the problem of pure confined water haven been investigated by our group in the last few years. The system studied consisted of a graphene pore modelled as two carbon (c0001) plates without defects filled with water. To have a complete characterization of the system, we have studied the same set-up at supercritical temperature. next, we have proceed to investigate the same sample with graphene walls but for aqueous ionic solutions, comparing potentials with and without polarization, various concentrations and ions of different sizes and polarizabilities (nai, nacl, naf). to study the role of the confining surface, the plane geometry have been changed to a silica nanotube. In this case the effect of the confining geometry on a non polarizable nacl solution have been studied for pores of different radius and changing the properties of the surface from hydrophobic to hydrophilic by means of oh groups functionalization. new insights about this systems and the specific ion effects are revealed through the analysis of structural, dynamic and dielectric properties. the force matching (fm) technique allows to obtain classical potentials by adjusting its free parameters to reproduce properties from ab initio trajectories. In the last section of this thesis, we refine the fm technique and apply it for the first time to obtain rigid water potential models with the inclusion of electrostatic damping. The potentials obtained with our approximation, fairly reproduce the main structural and dynamic properties from the ab initio simulations used for the fitting.
Datos académicos de la tesis doctoral «Confinement effects on the structure and dynamics of water and aqueous ionic solutions«
- Título de la tesis: Confinement effects on the structure and dynamics of water and aqueous ionic solutions
- Autor: JonÁ s Sala Viñas
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 09/05/2012
Dirección y tribunal
- Director de la tesis
- Elvira Guardia Manuel
- Tribunal
- Presidente del tribunal: joan angel Padro cardenas
- jordi Faraudo gener (vocal)
- mathieu Salanne (vocal)
- paola Gallo (vocal)