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Theory of sorption and electronic transport in amorphous polymers and single molecules

Research output: ThesisDoctoral Thesis

Publication date2020
Number of pages186
Awarding Institution
  • Lancaster University
<mark>Original language</mark>English


This thesis describes a series of studies of the energetics, structure, sorption and electronic transport of polymers and single molecules at the nanoscale.

The first of these relates to hypercrosslinked porous polymers, which are
of technological and commercial interest for their ability to efficiently absorb
molecules in a wide range of contexts from pharmaceuticals to gas storage.
I model a family of polymers synthesised by collaborators at the University
of Strathclyde, which show very high uptake of polyaromatic hydrocarbon
(PAH) molecules from solution and could potentially be used as a filtration material to remove these molecules from vehicle lubrication oils, where
they are responsible for the build up of soot and the long term degradation of both oil and engine. Density functional theory calculations identified
the structural units of the polymers contributing most to sorption, and the
relative binding strengths of several PAHs which correspond to the experimental trends. Molecular dynamics simulations of the polymer pores with
PAH molecules in a heptane solution highlighted the significance of polymer
flexibility and pore size in the sorption process.

In the second I analyse the conductance of the first organically synthesized
hybridized porous carbon, OSPC-1. This new carbon shows electron
conductivity, high porosity, the highest uptake of lithium ions of any carbon
material to-date, and the ability to inhibit dangerous lithium dendrite formation. It therefore has potential as an anode material for lithium-ion batteries
with high capacity, excellent rate capability, long cycle life, and potential
for improved safety performance. Detailed simulation of the variation of the
conductivity of this amorphous material versus length using a tight binding
methodology showed that the measured conductance is consistent with an
inelastic scattering length of the size of an OPSC-1 fragment.

The third project is in the field of molecular electronics, where a crucial
area of research aims to identify molecular anchor groups to bind molecules
to electrodes. This study presents a series of oligo(phenylene-ethynylene)
wires with one tetrapodal anchor and a phenyl or pyridyl head group. The
new anchors are designed to bind strongly to gold surfaces without disrupting
the conductance pathway of the wires. Density functional theory was used
to simulate the structures of the molecules and the nature of their binding
to the Au surface. Quantum transport calculations provided insight into the
conductance pathway through the molecules and confirmed the decoupling
between surface binding and electronic coupling. This feature may enable
the inclusion in junctions of a wider range of functional groups, in particular
those with strong electronic coupling, but only weak physical binding.