Darkins, R; (2017) Computational insight into the molecular mechanisms that control the growth of inorganic crystals. Doctoral thesis , UCL (University College London).

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Abstract

After billions of years of evolution, nature has developed mechanisms for controlling the growth and assembly of materials right down to the nanoscale, an achievement that materials scientists hope to mimic. However, the underlying processes are extremely complex and depend on subtle behaviour at the molecular scale. In contrast to experimental methods, computer simulations can achieve the molecular resolution needed to investigate these mechanisms, and can therefore offer unique insight. Indeed, this dissertation employs a variety of state-of-the-art computational methodologies to investigate the molecular processes by which calcite, the most abundant biomineral on earth, grows, in addition to the role played by surfactants in soft templating technologically important inorganic materials. Microsecond-long simulations are performed to reveal the behaviour of individual ions in the vicinity of calcite steps, providing new insight into the mechanisms responsible for kink nucleation. Rare event methodologies are then used to study the dissolution process of kink sites in calcite crystals. It is discovered that this particular mineralisation process is too complex to be tamed by computational methods, which has far-reaching consequences for the development of highly predictive models of mineralisation. A coarse-grained model for calcite precipitation is presented that displays the ability to connect molecular processes with both the kinetic and morphological characters of a crystal. However, the simulation is found to conflict with experimental observations regarding the dependence of step velocity on step length. The implication being that present models are unable to correctly describe step pinning, which is a major limitation. Lastly, the role of surfactants in templating crystal growth via two very different mechanisms is investigated. In the one case, polymorph and orientation selection by self-assembled monolayers; and in the other, oriented heterogeneous nucleation of mesoporous organosilicas.

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