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SS3.03 - Simulations of Calcite Crystaliization on Self-Assembled Monolayers 
April 23, 2014   9:30am - 9:45am

Ordered organic substrates, such as substrates functionalized with self-assembled monolayers (SAMs), are often used as model systems to study oriented crystal growth and attachment and to gain an understanding of biomineralization processes. Experimental [1] and modelling [2,3] results indicate that the substrate properties influence the crystal orientation but the detailed mechanisms involved in orientation control remain a topic of some debate.We have employed atomistic simulation methods to investigate calcium carbonate crystallization on SAMs, as such methods provide length and time scale resolution beyond the experimentally accessible regimes. Here we present results from a comprehensive study of the crystallization of calcium carbonate (CaCO3) on a range of carboxylate terminated alkyl thiols. The calculations use potential-based metadynamics with a simple Gaussian addition scheme to overcome the large energy barriers associated with crystal nucleation and growth. We investigate the effect of the alkyl chain length on the structure and energy of the resulting interfaces and find that the magnitude of the interfacial binding energy increases with the length of the alkyl chain. We also investigate the effect of substrate flexibility on orientation selection and find that rigid substrates induce crystallization of surfaces with a close epitaxial match (i.e the (001) orientation) whereas flexible substrates induce (012) oriented crystallization, which has a poorer match to the substrate. Calculations identified the (001) interface as the lower energy interface therefore we conclude that kinetic factors dominate calcite orientation selection on carboxylate SAMs and we propose a mechanism for the enhanced growth in the (012) orientation [4]. [1] J. Aizenberg, A. J. Black, G. M. Whitesides, J. Am. Chem. Soc. (1999), 121, 4500-4509.[2] D. M. Duffy and J. H. Harding, Langmuir (2004), 20, 7630-7636.[3] D. Quigley, P. M. Rodger, C. L. Freeman et al J. Chem. Phys. (2009), 131, 094703.[4] R.D. Darkins, A.S. Côté, C. L. Freeman and D. M. Duffy J. Cryst. Growth , 367 (2013) 110-114

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