This thesis studies the electrostatic interactions of ions in solution. This is a well studied but counter-intuitive field with many behaviours which defy conventional theoretical results, mainly as a result of the complexity of modelling the ions and the surrounding systems. Therefore this work endeavours to simplify the theoretical environment by considering ions under purely Coulombic interactions. A further simplification of this model is to consider the ions to be completely penetrable or ’ultrasoft’, i.e. the ions can pass through one another, this reduces the complexity of dealing with the excluded volume associated with the non-penetrable or ’hard core’ ions. This ’ultrasoft’ model is studied using both a variational mean field theory and a virial expansion in the first place and compared to integral equation methods such as the random phase approximation and the Hyper-netted chain theory as well as Monte Carlo (MC) simulations from the available literature. Then molecular dynamics simulations are used to test the model in various situations.The two main systems studied under this model are a symmetric electrolyte consisting of penetrable cations and anions with identical size and charge to one another,and an asymmetric electrolyte consisting of ultrasoft cations and point-charge anions. The Ultrasoft model requires a charge distribution to be defined within the theory, this work has examined both a Bessel and a Gaussian charge distribution for each of the symmetric and asymmetric cases.The symmetric model shows good agreement with MC simulations from the literature which allows for more extreme temperatures and densities to be studied. This study reveals like charged clustering at the low temperature-high density limit. The asymmetric model shows analogies with the classical one component plasma as the temperature of the system is decreased and the density is increased. The asymmetric model also shows clustering but it takes a different form to the symmetric electrolyte.
|Date of Award||14 May 2017|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Leo Lue (Supervisor) & Paul Mulheran (Supervisor)|