Tombari E, Salvetti G, Ferrari C, Johari G P
Istituto per i Processi Chimico-Fisici del CNR, via G. Moruzzi 1, 56124 Pisa, Italy.
Phys Chem Chem Phys. 2005 Oct 7;7(19):3407-11. doi: 10.1039/b510481e. Epub 2005 Aug 26.
Real time decrease in the energy (or enthalpy) measured during confinement of controlled amounts of water in 2 nm radius pores of Vycor shows that exothermic transfer of bulk water to nanopores via the vapour-phase occurred in two stages. In the first stage, at saturation pressure, H2O molecules from the vapour rapidly accumulated in the nanopore channels near the Vycor surface. In the second, at vapour pressure below saturation, the accumulation rate abruptly decreased and water (slowly) diffused and redistributed in the nanopore channels until the vapour pressure equilibrium was attained. The energy decrease per H2O molecule was highest, 14.5 kJ mol(-1), at low amounts when the pore-wall was incompletely covered by H2O. This value approached zero at higher amounts when pores were gradually filled. The results show that the vibrational and configurational contributions to the energy of H2O molecules depend upon their position in the nanopore and these contributions approach their bulk water values at high water concentration, but do not attain those values for completely filled pores.
在将受控量的水限制在半径为2纳米的Vycor孔隙中时，所测量到的能量（或焓）的实时下降表明，大量水通过气相向纳米孔的放热转移分两个阶段发生。在第一阶段，在饱和压力下，来自气相的H₂O分子迅速在Vycor表面附近的纳米孔通道中积累。在第二阶段，在低于饱和的蒸气压下，积累速率突然下降，水（缓慢地）在纳米孔通道中扩散和重新分布，直到达到蒸气压平衡。当孔壁未被H₂O完全覆盖且水量较低时，每个H₂O分子的能量下降最高，为14.5 kJ mol⁻¹。当孔隙逐渐被填满且水量较高时，该值接近零。结果表明，H₂O分子能量的振动和构型贡献取决于它们在纳米孔中的位置，并且在高水浓度下这些贡献接近其在大量水中的值，但对于完全填满的孔隙，并未达到这些值。
