INVESTIGADORES
ELOLA Maria Dolores
artículos
Título:
Confined Polar Mixtures within Cylindrical Nanocavities
Autor/es:
RODRIGUEZ JAVIER; ELOLA, MARÍA DOLORES; LARIA D
Revista:
JOURNAL OF PHYSICAL CHEMISTRY B - (Print)
Editorial:
AMER CHEMICAL SOC
Referencias:
Lugar: WASHINGTON, DC ; Año: 2010 vol. 114 p. 7900 - 7908
ISSN:
1520-6106
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 R-cnt = 0.55 nm, and (16,16) ones, with R-cnt = 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
similar to 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 similar to 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.