8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P7.116Thu 811:10-14:00Computer simulation study of dynamic crossoverphenomena in nanoconfined waterGiuseppe B. Suffritti, 1 Pierfranco Demontis, 1 and Marco Masia 11 Dipartimento di Chimica, Università di Sassar, Via Vienna, 2, I-07100, Sassari,ItalyIn order to study the dynamic crossover phenomena in nanoconfined water, we performed a seriesof molecular dynamics (MD) computer simulations of water clusters adsorbed in zeolites, whichare microporous crystalline aluminosilicates, whose channels and cavities are of nanometric dimensions.We used a sophisticated empirical potential for water, including the full flexibility ofthe molecule and of the aluminosilicate framework. [1, 2]. The results of the simulations of waterconfined in a variety of zeolites (worm-like clusters in silicalite [1], spherical nano-clustersin zeolite A [3], cross-linked nanowires in NaX and ice-like nanotubes in AlPO4-5 and SSZ-24[1]) at different temperatures and coverage (loading) are discussed in connection with the experimentaldata. Preliminary results of Car-Parrinello MD simulations of water in vermiculite clayare also shown. In particular, dynamic crossover phenomena are found for the adsorbed waterin all the considered cases, in spite of the different shape and size of the clusters, even when theconfinement hinders the formation of tetrahedral hydrogen bonds for water molecules. They wereevidenced by inspecting the trends of rotational relaxation constants and of spectral contributionsto vibrational spectra vs. temperature. Dynamical crossover temperatures were detected around220 K and 160 K, corresponding to those found experimentally in many hydrated systems, suchas aqueous solutions, oxide surfaces, clays, proteins and cement paste. Based on a detailed analysisof the single-molecule dynamical behaviour, hypotheses about the possible dynamic crossovermechanisms are proposed.[1] P. Demontis et al. J. Phys. Condens. Matter, 22, 284106 (2010).[2] P. Demontis et al. Micropor. and Mesopor. Mater. 125, 160 (2009).[3] P. Demontiset al ACS Nano 2, 1603 (2008)116