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Title: Modelling surface thermodynamics and intrinsic optical properties of the air-water interface
Author: Longford, Francis G. J.
ISNI:       0000 0004 7224 9673
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2017
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Intrinsic surface sampling techniques are used to analyse MD simulations of the air-water interface in order to investigate reports of anomalous optical behaviour recently uncovered by ellipsometry. In doing so, a new approach to calculating surface thermodynamic properties has been described and an overlooked finite size e↵ect a↵ecting surface tension measurements has been uncovered. A correction has also been developed to reduce a fitting bias in the intrinsic sampling method (ISM), which leads to a non-Gaussian distribution of mean curvature at interfacial molecular coordinates on a parametrised intrinsic surface. Consequently, it is now possible to reduce artefacts that prevent successful mapping back of the intrinsic density to the global density at high resolutions via convolution along the axis normal to the interface. A further method has been developed to estimate the local linear optical properties of interface regions, with application to the prediction of ellipsometry experiments. The e↵ective medium approximation for the dielectric permittivity of a system possessing a non-homogeneous polarisation density distribution is combined with an intrinsic surface technique describing the structure of the interface region as a Fourier series. It is concluded that employing the this description allows for optical properties of the air-water interface to be revealed from classical molecular dynamics simulations that are distinct from other polar solvents (methanol), and lie in agreement with new experimental data. This investigation also provides new pathways to determine a more robust description of the intrinsic surface and explores new simulation tools using extended capillary wave theories.
Supervisor: Frey, Jeremy Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available