INQUIMAE   12526
INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
artículos
Título:
Confined polar mixtures within cylindrical nanocavities
Autor/es:
J. RODRIGUEZ, M. D. ELOLA Y D. LARIA
Revista:
JOURNAL OF PHYSICAL CHEMISTRY B
Editorial:
American Chemical Society
Referencias:
Lugar: Washington DC; Año: 2010 vol. 114 p. 7900 - 7908
ISSN:
1089-5647
Resumen:
Using molecular dynamics experiments, we have extended our previous
analysis of equimolar mixtures of water and acetonitrile confined
between silica walls [ J. Phys. Chem. B 2009, 113,
12744] to examine similar solutions trapped within carbon nanotubes and
cylindrical silica pores. Two different carbon tube sizes were
investigated, (8,8) tubes, with radius Rcnt = 0.55 nm, and (16,16) ones, with Rcnt
= 1.1 nm. In the narrowest tubes, we found that the cylindrical cavity
is filled exclusively by acetonitrile; as the radius of the tube
reaches 1
nm, water begins to get incorporated within the inner cavities. In
(16,16) tubes, the analysis of global and local concentration
fluctuations shows a net increment of the global acetonitrile
concentration; in addition, the aprotic solvent is also the prevailing
species at the vicinity of the tube walls. Mixtures confined within
silica nanopores of radius 1.5
nm were also investigated. Three pores, differing in the effective
wall/solvent interactions, were analyzed, (i) a first class, in which
dispersive forces prevail (hydrophobic cavities), (ii) a second type,
where oxygen sites at the pore walls are transformed into polar silanol
groups (hydrophilic cavities), and (iii) finally, an intermediate
scenario, in which 60% of the OH groups are replaced by mobile
trimethylsilyl groups. Within the different pores, we found clear
distinctions between the solvent layers that lie in close contact with
the silica substrate and those with more central locations. Dynamical
modes of the confined liquid phases were investigated in terms of
diffusive and rotational time correlation functions. Compared to bulk
results, the characteristic time scales describing different solvent
motions exhibit significant increments. In carbon nanotubes, the most
prominent modifications operate in the narrower tubes, where
translations and rotations become severely hindered. In silica
nanopores, the manifestations of the overall retardations are more
dramatic for solvent species lying at the vicinity of trimethylsilyl
groups.