Departamento de Química Inorgánica Analítica y Química-Física e INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina.
J Chem Phys. 2011 Sep 14;135(10):104503. doi: 10.1063/1.3632050.
Molecular dynamics simulations have been carried out to investigate structural and dynamical characteristics of NaCl aqueous solutions confined within silica nanopores in contact with a "bulk-like" reservoir. Two types of pores, with diameters intermediate between 20 Å and 37.5 Å, were investigated: The first one corresponded to hydrophobic cavities, in which the prevailing wall-solution interactions were of the Lennard-Jones type. In addition, we also examined the behavior of solutions trapped within hydrophilic cavities, in which a set of unsaturated O-sites at the wall were transformed in polar silanol Si-OH groups. In all cases, the overall concentrations of the trapped electrolytes exhibited important reductions that, in the case of the narrowest pores, attained 50% of the bulk value. Local concentrations within the pores also showed important fluctuations. In hydrophobic cavities, the close vicinity of the pore wall was coated exclusively by the solvent, whereas in hydrophilic pores, selective adsorption of Na(+) ions was also observed. Mass and charge transport were also investigated. Individual diffusion coefficients did not present large modifications from what is perceived in the bulk; contrasting, the electrical conductivity exhibited important reductions. The qualitative differences are rationalized in terms of simple geometrical considerations.
采用分子动力学模拟方法研究了与“块状”储层接触的二氧化硅纳米孔中 NaCl 水溶液的结构和动力学特性。研究了两种直径在 20 Å 和 37.5 Å 之间的孔：第一种是疏水性空腔，其中壁-溶液相互作用主要是 Lennard-Jones 类型。此外，我们还研究了被困在亲水性空腔内溶液的行为，其中壁上的一组不饱和 O 位被转化为极性硅醇 Si-OH 基团。在所有情况下，被困电解质的总浓度都表现出重要的降低，在最窄的孔中，达到了体相值的 50%。腔内的局部浓度也表现出重要的波动。在疏水性空腔中，孔壁的近邻完全被溶剂覆盖，而在亲水性空腔中，也观察到 Na(+) 离子的选择性吸附。还研究了质量和电荷输运。与在体相中观察到的情况相比，单个扩散系数没有发生大的变化；相反，电导率表现出显著的降低。定性差异可以根据简单的几何考虑来解释。
