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Title: Computer simulation of mesocrystals
Author: Růžička, Štěpán
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2014
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The mesoscale is a thousand times larger than the atomistic scale with colloidal particles, rather than atoms or molecules, forming the constituent building blocks for organized structures. Nanotechnology has recently started interpreting colloidal units as colloidal molecules, and a lot of interest emerged in their assembly into self-organized structures called colloidal crystals. A mesocrystal is a special type of colloidal crystal, where constituent colloidal units are crystallographically registered nanocrystals. Computer simulation of colloidal self-assembly requires coarse-graining, where short-range attraction is usually the dominant force on the colloidal scale. In this thesis, moderately deep quenches of short-range attractive spherical colloids at low packing fractions are performed, because strong clustering into liquid drops preceding crystallization is known to follow quenching and is reminiscent of mesocrystallization. Moreover, variation of simulation parameters in those models allows an easy investigation of the competition between the fundamental processes of multiscale assembly such as coarsening, crystallization, gelation, and phase separation interfering with the dynamical slowing down. Since colloidal building blocks are usually characterized by complex anisotropic interactions we use Monte Carlo rather than dynamical simulations. The thesis is focused on the development of the Virtual Move Monte Carlo which is a Monte Carlo cluster algorithm selecting the moving clusters according to the local energy gradients. The algorithm allows one to control the rates of local crystal evolution and a larger scale cluster aggregation. The thesis investigates the conditions at which the crystallization precedes the aggregation and vice versa. It is confirmed by the Monte Carlo simulations that the properties of kinetically slowed down structures are independent of the microscopic dynamics, and that three different linear growth regimes, correlated to the local order, are present in systems where structure evolves mainly via single particle exchange. It is also shown that long-range repulsions are necessary to stabilize the phase separated aggregates, and that a renormalization of the repulsion leads to a significant decrease of polydispersity of the liquid or recrystallized drops. The efficiency of rotational cluster moves simulating the alignment into crystallographic register is enhanced by several orders of magnitude in this thesis. The results are discussed in the language of recent colloidal physics and related to a wider range of coarsening and self-assembly phenomena observed during the nonclassical crystallization or mesocrystallization processes.
Supervisor: Not available Sponsor: University of Warwick ; Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics