I am a computational chemist with an interest in understanding interfaces.
I use physical chemistry to try and understand fundamental issues related to interfacial phenomena. In particular I use molecular modelling to try and understand issues related to the Earth and the environment.
In my spare time I enjoy playing guitar, riding bikes, kicking footballs, and climbing mountains.
Fine-grained sediments and sedimentary rocks play important roles in a variety of modern energy technologies from petroleum geology to geological carbon sequestration and radioactive waste management. However, despite their utility and ubiquity, many of their properties remain poorly understood. In particular, the ability to predict the permeability and mechanics of these media remains a persistent fundamental challenge in the geosciences. In the present work, we show how large-scale classical molecular dynamics (MD) simulations can help interpret the properties of fine-grained sedimentary material. All-atom simulations containing 30 discrete clay particles are utilized to understand the evolution of a clay nanoparticle suspension during its progressive dehydration. Microstructural (pore size distribution, tortuosity, anisotropy), thermodynamic (enthalpy and free energy of hydration, anion exclusion), mechanical (total suction), and transport properties (diffusion coefficient tensors of water and sodium) are calculated and compared to the experiment. Overall, our results provide new insight into the coupled chemistry, mechanics, and transport properties of disordered nanoparticle assemblages and shed light upon the important role of water films in controlling these properties.
@article{underwood2020large,title={Large-scale molecular dynamics simulation of the dehydration of a suspension of smectite clay nanoparticles},author={Underwood, Thomas R and Bourg, Ian C},doi={10.1021/acs.jpcc.9b11197},journal={The Journal of Physical Chemistry C},volume={124},number={6},pages={3702--3714},year={2020},publisher={American Chemical Society},}
J Phys Chem B
Dielectric Properties of Water in Charged Nanopores
In this study, we examine the spectral dielectric properties of liquid water in charged nanopores over a wide range of frequencies (0.3 GHz to 30 THz) and pore widths (0.3 to 5 nm). This has been achieved using classical molecular dynamics simulations of hydrated Na-smectite, the prototypical swelling clay mineral. We observe a drastic (20-fold) and anisotropic decrease in the static relative permittivity of the system as the pore width decreases. This large decrement in static permittivity reflects a strong attenuation of the main Debye relaxation mode of liquid water. Remarkably, this strong attenuation entails very little change in the time scale of the collective relaxation. Our results indicate that water confined in charged nanopores is a distinct solvent with a much weaker collective nature than bulk liquid water, in agreement with recent observations of water in uncharged nanopores. Finally, we observe remarkable agreement between the dielectric properties of the simulated clay system against a compiled set of soil samples at various volumetric water contents. This implies that saturation may not be the sole property dictating the dielectric properties of soil samples, rather that the pore-size distribution of fully saturated nanopores may also play a critically important role.
@article{underwood2022dielectric,title={Dielectric Properties of Water in Charged Nanopores},author={Underwood, Thomas R and Bourg, Ian C},journal={The Journal of Physical Chemistry B},volume={126},number={14},pages={2688--2698},year={2022},publisher={American Chemical Society},doi={10.1021/acs.jpcb.1c09688},}
