Coarse-Grained Models of Ionic Solutions

Ryan Szparaga

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Room-temperature ionic liquids (RTILs) are compounds composed entirely of ions, which are liquid at temperatures below 100 degrees Celsius. Their high ionic strength and strong coupling make them useful for a number of applications, e.g. as electrolytes in supercapacitors. These properties also make them interesting subjects for theoretical research, as the canonical theories of the electrical double layer fail under these conditions. We implement coarse-grained models of RTILs into Monte Carlo (MC) simulations and Classical Density Functional Theory (DFT) to investigate their behaviour at electrode surfaces.
A prewetting transition is found for a dilute RTIL and solvent mixture, with a large differential capacitance spike found in the sub critical region. Investigation of capillary condensation for a similar mixture in a pore yields another differential capacitance spike, which decreases away from critical conditions. DFT and MC are compared for a new model RTIL with the former containing a new innovation in describing charge-charge correlations, which gives good agreement for fluid structures at a surface. Pressure-distance curves are computed with DFT for a homologous series of aromatic RTILs, showing the range of interactions to increase with alkyl chain length. Increasing surface charge density causes the amplitude of the interaction free energy curves to decrease.
Image charge interactions are examined for a primitive model electrolyte using MC and a new image-corrected Poisson-Boltzmann DFT formulism (iPB), that record good agreement. Increasing salt concentration enhances the desolvation repulsion, and incorporating a basic model for specific adsorption predicts that a colloidal dispersion can be stabilised in this way.
The final paper discusses DFT formulism in detail for ionic systems, including new results. We find that increasing the surface exclusion zone reduces the differential capacitance, raising the temperature can enhance the differential capacitance and specific adsorption of charged components diminishes the characteristic minimum of the 'camel-hump'.
Original languageEnglish
QualificationDoctor
Awarding Institution
  • Computational Chemistry
Supervisors/Advisors
  • Forsman, Jan, Supervisor
Award date2015 Mar 13
Publisher
ISBN (Print)978-91-7422-390-3
Publication statusPublished - 2015

Bibliographical note

Defence details

Date: 2015-03-13
Time: 10:30
Place: Lecture Hall B

External reviewer(s)

Name: Kahl, Gerhard
Title: Univ.Prof.Dr.
Affiliation: Vienna University of Technology

---




The information about affiliations in this record was updated in December 2015.
The record was previously connected to the following departments: Theoretical Chemistry (S) (011001039)

Subject classification (UKÄ)

  • Theoretical Chemistry

Free keywords

  • Monte Carlo
  • Classical Density Functional Theory
  • Coarse-Grained Models
  • Ionic Liquids
  • Prewetting
  • Capillary Condensation
  • Electric Double Layer
  • Differential Capacitance.

Fingerprint

Dive into the research topics of 'Coarse-Grained Models of Ionic Solutions'. Together they form a unique fingerprint.

Cite this