Naslov
Molecular dynamics study of methanol/water and methanol/acetone mixtures

Autori
Sokolić, Franjo ; Polok, Kamil ; Zoranić, Larisa ; Mazighi, Redha ; Perera, Aurélien

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
EMLG-JMLG Meeting 2009-Book of Abstracts / Musso, Maurizio ; Heissl Claudia - Salzburg : Universitat Salzburg, 2009

Skup
Intermolecular Interactions and Liquid Structure, EMLG/JMLG Annual Meeting 2009

Mjesto i datum
Salzburg, Austrija, 06.09.2009. - 10.09.2009

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
water mixtures; MD simulations

Sažetak
Molecular Dynamics study of the structural properties of the two mixtures, namely methanol/water and methanol/ acetone, is presented, with the focus on the difference in their micro-structure. The differences in micro-structure of the three neat liquids have been previously analyzed. Neat acetone micro-structure is very disordered, ruled essentially by the excluded volume effect [1]. Liquid methanol has been shown [2] to form chain-like structures with various topologies: the amphyphilicity of this molecule leads to typical clusters, where oxygen atoms through hydrogen bonding form open chains, while methyl groups are homogeneously distributed around these chains. The status of neat water is more complex, with highly non-trivial dual structural organizations [3]. These very different structural features are then translated in the differences in the structural organization of the corresponding mixtures. Results show higher structural complexity in the methanol/water mixtures. The structural functions of water show large variation of the long-range correlations. This is attributed to the fact that water is highly associated in an extended network and variation of the tail represents sampling over different realizations of these associations. Liquid water seems to have a peculiar dynamical "supra" structure, which has a half-life of the order of the hundred picoseconds, which is also the typical sampling time over which the averaging is done. This implies much longer runs (nanosecond scale), in order to recover correct asymptotic values. Methanol-acetone mixture shows no such variations in the long range part of the structural features, which means that there are no dynamical processes at the time scale of sampling. An interesting difference between the two mixtures concerns the asymptotic limit of the site-site radial distribution functions (RDFs). It is well known that, in N constant ensembles, the RDFs do not tend to one, but to values in relation to the compressibility of the system [4]. We observe that aqueous mixture have RDFs that go nearly to one, while the other mixtures are very distinctly shifted. This is an indirect indication that the aqueous solutions are more rigid (less compressible) than non-aqueous mixtures. [1] Perera A. and Sokolic F., “Modeling nonionic aqueous solutions: The acetone-water mixture“, Journal of Chemical Physics , 12 (22), 11272-11282 (2005) [2]. Zoranic L., Sokolic F. and Perera A., “Microstructure of neat alcohols: A molecular dynamics study“, Journal of Chemical Physics, 127, 024502-10 (2007) [3] Perera A., Rispe A., Zoranic L., Mazighi R. and Sokolic F., “Water-like structure with repulsive double-core interactions“, Molecular Physics, in press [4] Lebowitz, J. L. and. Percus J. K., “Long-Range Correlation in a Closed System with Applications to Nonuniform Fluids”, Physical Review, 122 (6), 1675-1691 (1961)

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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