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arXiv 1306.5132cond-mat.soft
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压力作用下纳米承压水的动力学研究

Dynamics of Nano-Confined Water under Pressure

S. O. Diallo, M. Jazdzewska, J. C. Palmer, E. Mamontov, K. E. Gubbins, M. Sliwinska-Bartkowiak

摘要:

研究了压力对平均孔径为16埃的单壁碳纳米管中水分子扩散系数的影响。测量使用高分辨率中子散射,在220 < T < 260 K的温度范围内,并在两种压力条件下进行:环境压力和升高的压力。高压数据是在冷却时以恒定体积收集的,P从温度T = 260 K时的1.92 kbar变化到温度T = 220 K时的1.85 kbar。所观察到的动态结构因子S(Q,E)的分析揭示了存在两个弛豫过程,一个更快的扩散组件(FC)与运动的“笼”或限制分子,和一个较慢的组件所产生的自由水分子扩散内的单壁碳纳米管矩阵。虽然缓慢弛豫时间的温度依赖性表现出Vogel-Fulcher-Tammann定律,并且在性质上是非Arkenius的,但更快的分量在两种压力条件下都遵循Arkenius指数定律。压力的应用显着减慢了整体分子动力学,与以前的观察结果一致,但最显着的影响慢松弛。在实验条件下,更快的弛豫随压力变化不大或没有变化。

英文摘要:

We report a study of the effects of pressure on the diffusivity of water molecules confined in single- wall carbon nanotubes (SWNT) with average mean pore diameter of 16 Angstroms. The measurements were carried out using high-resolution neutron scattering, over the temperature range 220 < T < 260 K, and at two pressure conditions: ambient and elevated pressure. The high pressure data were collected at constant volume on cooling, with P varying from 1.92 kbar at temperature T = 260 K to 1.85 kbar at T = 220 K. Analysis of the observed dynamic structure factor S(Q, E) reveals the presence of two relaxation processes, a faster diffusion component (FC) associated with the motion of "caged" or restricted molecules, and a slower component arising from the free water molecules diffusing within the SWNT matrix. While the temperature dependence of the slow relaxation time exhibits a Vogel-Fulcher-Tammann law and is non-Arrhenius in nature, the faster component follows an Arrhenius exponential law at both pressure conditions. The application of pressure remarkably slows down the overall molecular dynamics, in agreement with previous observations, but most notably affects the slow relaxation. The faster relaxation shows marginal or no change with pressure within the experimental conditions.

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