Departamento de Física, Comisión Nacional de Energía Atómica, Avenida Libertador 8250, 1429 Buenos Aires, Argentina.
J Chem Phys. 2010 Oct 21;133(15):154707. doi: 10.1063/1.3503886.
Molecular dynamics simulations have been carried out to investigate the structure and dynamics of liquid methanol confined in 3.3 nm diameter cylindrical silica pores. Three cavities differing in the characteristics of the functional groups at their walls have been examined: (i) smooth hydrophobic pores in which dispersive forces prevail, (ii) hydrophilic cavities with surfaces covered by polar silanol groups, and (iii) a much more rugged pore in which 60% of the previous interfacial hydroxyl groups were replaced by the bulkier trimethylsilyl ones. Confinement promotes a considerable structure at the vicinity of the pore walls which is enhanced in the case of hydroxylated surfaces. Moreover, in the presence of the trimethylsilyl groups, the propagation of this interface-induced spatial ordering extends down to the central region of the pore. Concerning the dynamical modes, we observed an overall slowdown in both the translational and rotational motions. An analysis of these mobilities from a local perspective shows that the largest retardations operate at the vicinity of the interfaces. The gross features of the rotational dynamics were analyzed in terms of contributions arising from bulk and surface states. Compared to the bulk dynamical behavior, the characteristic timescales associated with the rotational motions show the most dramatic increments. A dynamical analysis of hydrogen bond formation and breaking processes is also included.
采用分子动力学模拟方法研究了直径为 3.3nm 的圆柱形二氧化硅孔中甲醇液体的结构和动力学性质。考察了三种不同官能团特性的孔壁空腔：（i）具有分散力优势的光滑疏水孔；（ii）由极性硅醇基团覆盖的亲水空腔；（iii）由 60%的界面羟基基团被较大的三甲基硅基取代的更为粗糙的孔。受限作用促进了孔壁附近结构的显著变化，而在羟基化表面的情况下则进一步增强。此外，在三甲基硅基存在的情况下，这种界面诱导的空间有序性的扩展延伸到了孔的中心区域。关于动力学模式，我们观察到平移和旋转运动的整体减速。从局部角度对这些迁移率进行分析表明，最大的延迟作用发生在界面附近。采用体相和表面相的贡献对旋转动力学的总体特征进行了分析。与体相动力学行为相比，与旋转运动相关的特征时间尺度显示出最显著的增加。还包括对氢键形成和断裂过程的动力学分析。
