INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
congresos y reuniones científicas
POLAR MIXTURES UNDER NANOCONFINEMENT
LARIA, DANIEL HECTOR
Conferencia; 8th Liblice Conference on the Statistical Mechanics of Liquids; 2010
Czech Academy of Science
POLAR MIXTURES UNDER NANOCONFINEMENTWe present results from Molecular Dynamics experiments describing structural and dynamical characteristics of water (W)-acetonitrile (ACN) mixtures confined in three different environments of nanometric dimensions. The first one corresponds to two silica walls separated at distances d= 0.6, 1 and 1.5 nm with different hydrophobic characteristics. For fully hydrophobic environments, we found that, at the shortest interplate distance examined, the confined region is devoid of water molecules. At interplate distance of the order of 1 nm, water moves into the confined region, although in all cases, there is a clear enhancement of the local concentration of ACN in detriment of that of W. Dynamical characteristics of the solvent mixture are analyzed in terms of diffusive and rotational motions in both environments. In the second case, the confinement is provided by a membrane of (16,16) carbon nanotubes connecting two reservoirs, initially filled with W and ACN. Within the hydrophobic nanotube cavities, the equilibrium concentrations contrast sharply to those observed at the reservoirs, with a clear enhancement of ACN, in detriment of W. From the dynamical side, the relaxation involves three well differentiated stages: the first one corresponds to the equilibration of individual concentrations within the nanotubes. An intermediate interval with Fickian characteristics follows, during which the overall transport can be casted in terms of coaxial opposite fluxes, with a central water domain segregated from an external ACN shell, in close contact with the tube walls. We also found evidence of a third, much slower, mechanism to reach equilibration, which involves structural modifications of tightly bound solvation shells, in close contact with the nanotube rims. The third environment correspond to cylindrical silica nanopores with diameter close to 3 nm. In these cases our analysis will focus on how the structural and dynamical characteristics of the confined liquids are modified by the functionalization operated at the pore walls.