INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
Polar Mixtures under nanoconfinement
RODRIGUEZ, J.; ELOLA, M. D.; LARIA, D.
JOURNAL OF PHYSICAL CHEMISTRY B
American Chemical Society
Lugar: Washington DC; Año: 2009 vol. 113 p. 12744 - 12744
We present results from molecular dynamics simulations describing structuraland dynamical characteristics of equimolar mixtures of water and acetonitrile,confined between two silica walls separated at inter-platedistances $d= 0.6, 1$ and 1.5 nm. Two different environmentswere investigated: a first one, where wall-solvent dispersion forcesprevail (hydrophobic confinement) and a second one, in which the terminal O-atoms atthe silica surface are transformed into silanol groups (hydrophilic confinement).For the former case, we found that, at the shortest interplate distance examined,the confined region is devoid of water molecules. Atinterplate distance of the order of 1 nm, water moves into the confined region, althoughin all cases, there is a clear enhancement of the local concentration of acetonitrilein detriment of that of water. Within hydrophilic environments, we found clear distinctionsbetween a layer of bound water lying in close contact with the silica substrates,and a minority of confined water that occupies the innerliquid slab. The bound aqueous layer is fully coordinated to the silanol groups andexhibits minimal hydrogen bonding with the second solvation layer, which exclusivelyincludes acetonitrile molecules. Dynamical characteristics of the solvent mixture areanalyzed in terms of diffusive and rotational motions in both environments.Compared to bulk mixtures, we found significant retardations in all dynamicalmodes, being the most dramatic, those ascribed to water molecules boundto the hydrophilic plates.