Development of short range sticky site models for molecular dynamics simulation of the thermodynamic, interfacial, and transport properties of associating fluids
File(s)
Author(s)
Fairhurst, Karl Mark
Type
Thesis
Abstract
Association, most typically hydrogen bonding, is represented in the thermodynamic perturbation theory (TPT1) and its implementation in the SAFT equation of state using short-ranged
off-centred square-well (SW) sites which decorate an isotropic reference fluid. Recent interest
in the utilisation of SAFT as a force field parametrisation tool [Mu¨ller & Jackson, Annu. Rev.
Chem. Biomol. Eng., 5:405, (2014)] has highlighted a limitation of SW association sites, as
these models cannot readily be implemented in continuous molecular dynamics (MD) simulations, where both transport and thermodynamic properties can be obtained. Herein lies the
crux of the work presented in this thesis, which aims to address three salient research questions regarding SAFT associating coarse-grained (CG) force fields: 1) Can SAFT associating
force fields be adapted for molecular dynamics? 2) What are the limitations of the SAFT
parametrised associating force fields? and 3) Can associating SAFT force fields be used to
accurately predict the transport properties of real fluids?
A methodology is presented to map SW association sites onto analogous continuous forms by
equating the free energy contribution of both potentials, the SW contribution evaluated through
the correlations for the association kernels TPT1 and the continuous potentials using a Monte
Carlo (MC) numerical integration technique. The validity of this approach is established by
a three-way comparison of the thermodynamic properties of the new models (obtained using
MD) with those from the original SW models (obtained using MC) and the corresponding
SAFT theory. Current limitations of the theory are also identified, a new association kernel is
presented to address this, and the physical significance of model parameters are probed.
CG models with explicit association are presented for prototypical associating molecules, including hydrogen sulphide, ammonia, methylamine, methanol, ethanol, butanol, tertiary-butanol,
octanol, and water. MD simulations of these models reveal a trade-off between an accurate description of the thermodynamic equilibrium properties, particularly for the vapour phase, and
the reliable prediction of transport properties such as self-diffusion coefficients and viscosities.
off-centred square-well (SW) sites which decorate an isotropic reference fluid. Recent interest
in the utilisation of SAFT as a force field parametrisation tool [Mu¨ller & Jackson, Annu. Rev.
Chem. Biomol. Eng., 5:405, (2014)] has highlighted a limitation of SW association sites, as
these models cannot readily be implemented in continuous molecular dynamics (MD) simulations, where both transport and thermodynamic properties can be obtained. Herein lies the
crux of the work presented in this thesis, which aims to address three salient research questions regarding SAFT associating coarse-grained (CG) force fields: 1) Can SAFT associating
force fields be adapted for molecular dynamics? 2) What are the limitations of the SAFT
parametrised associating force fields? and 3) Can associating SAFT force fields be used to
accurately predict the transport properties of real fluids?
A methodology is presented to map SW association sites onto analogous continuous forms by
equating the free energy contribution of both potentials, the SW contribution evaluated through
the correlations for the association kernels TPT1 and the continuous potentials using a Monte
Carlo (MC) numerical integration technique. The validity of this approach is established by
a three-way comparison of the thermodynamic properties of the new models (obtained using
MD) with those from the original SW models (obtained using MC) and the corresponding
SAFT theory. Current limitations of the theory are also identified, a new association kernel is
presented to address this, and the physical significance of model parameters are probed.
CG models with explicit association are presented for prototypical associating molecules, including hydrogen sulphide, ammonia, methylamine, methanol, ethanol, butanol, tertiary-butanol,
octanol, and water. MD simulations of these models reveal a trade-off between an accurate description of the thermodynamic equilibrium properties, particularly for the vapour phase, and
the reliable prediction of transport properties such as self-diffusion coefficients and viscosities.
Version
Open Access
Date Issued
2020-03
Date Awarded
2020-07
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Muller, Erich
Jackson, George
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)