Bano, Anthony M. (2012) Polymorphism in biomineral nanoparticles. PhD thesis, University of Warwick.

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Abstract

Biomineralisation is the process by which living things produce hard mineral tissues with unique physical properties. The study of this process can help us produce biomimetic materials, reproducing such properties, with the study of nucleation and crystallisation of the materials being particularly important. I have used molecular simulation techniques to help gain a greater understanding of these processes, focussing particularly on identifying the conformations and solid phases available to nanoparticles of two biomineral compounds. The bones and teeth of mammals are made largely of calcium phosphates. I have used metadynamics to study nanoparticles of tricalcium phosphate (TCP) and have identified high and lower order configurations. To facilitate this work I reviewed the extant empirical potentials for calcium phosphate systems, selecting the most appropriate for TCP. Calcium carbonate, found in examples throughout the animal kingdom, has three crystalline polymorphs relevant to biomineralisation: calcite, aragonite and vaterite. While nanoparticles of calcite have been extensively studied the other polymorphs have been neglected to date. In this work I present a technique for predicting crystalline morphologies for all three polymorphs across a range of sizes, and compare the energetic ordering. In water the energetic ordering of the nanoparticles is heavily dependent on nanoparticle size. Furthermore, I present work calculating the surface enthalpies of a variety of calcium carbonate surfaces, many of which are negative. It appears that entropic penalty of ordered water is key to understanding the stability of nanocrystals. Also presented is an application of the nudged elastic band method to study transitions between nanoparticle crystal conformations. Between all three crystal polymorphs the nanoparticles passed through an amorphous region of phase space. These results have also been used to evaluate order parameters for use in metadynamics simulations.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QH Natural history
Library of Congress Subject Headings (LCSH):	Biomineralization, Biomimetic materials -- Mathematical models, Calcium carbonate -- Mathematical models, Nanoparticles -- Mathematical models
Date:	July 2012
Institution:	University of Warwick
Theses Department:	Molecular Organisation and Assembly in Cells
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Rodger, Mark ; Quigley, David, Ph.D.
Description:	Supplementary material can be found on CD housed with hard copy - please see Official URL for details of how to access this.
Extent:	xi, 207 leaves : ill., charts
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/49891

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