[论文解读] Observation of the Anomalously Slow (Power-Law) Relaxation of the System of Interacting Liquid Nanoclusters in the Disordered Confinement of a Random Porous Medium

V. D. Borman, А. А. Белогорлов+1 more|arXiv (Cornell University)|May 20, 2015

Material Dynamics and Properties参考文献 5被引用 3

一句话总结

本研究调查了在Libersorb 23的无序纳米孔中压力释放后，水纳米团簇的异常缓慢松弛行为。通过时间分辨的填充度测量，发现其在约10⁵秒的时间范围内呈现幂律衰减，幂律指数α < 0.1，该现象归因于充满孔道的连通网络中相互作用的液态团簇，揭示了受限无序系统中的非平衡动力学行为。

ABSTRACT

The time evolution of the system of water in the Libersorb 23 (L23) disordered nanoporous medium after the complete filling at excess pressure and the subsequent removal of excess pressure has been studied. It has been found that three stages can be identified in the relaxation of the L23-water system under study. At the first stage, a portion of water at the removal of excess pressure rapidly flows out in the pressure reduction time, i.e., following a decrease in the pressure. It has been shown that, at temperatures below the dispersion transition temperature $T &lt; T_d = 284 K$, e.g., $T = 277 K$, the degree of filling $θ$ decreases from 1 to 0.8 in 10 s, following the variation of excess pressure. At the second stage of relaxation, the degree of filling $θ$ varies slowly according to a power law $θ \sim t^{-α}$ with the exponent $α &lt; 0.1$ in the time $t \sim 10^5$ s. This corresponds to a slow relaxation of the formed metastable state of the nonwetting liquid in the porous medium. At the third stage when $t &gt; 10^5$ s, the formed metastable state decays, which is manifested in the transition to a power-law dependence $θ(t)$ with a larger exponent. The extrusion-time distribution function of pores has been calculated along with the time dependence of the degree of filling, which qualitatively describes the observed anomalously slow relaxation and crossover of the transition to the stage of decay with a power-law dependence $θ(t)$ with a larger exponent. It has been shown that the relaxation and decay of the metastable state of the confined nonwetting liquid at $θ&gt;{θ_c}$ are attributed to the appearance of local configurations of liquid clusters in confinement and their interaction inside the infinite percolation cluster of filled pores.

研究动机与目标

• 理解压力释放后，液态水在无序多孔介质中非平衡松弛动力学的行为。
• 识别在受限条件下处于亚稳态、非润湿液态时，出现异常缓慢松弛的物理起源。
• 表征填充度（θ）随时间的演化，并将其与孔道网络结构及团簇相互作用关联。
• 通过孔道排出时间分布建模，解释从缓慢幂律衰减到更快速衰减的过渡行为。

提出的方法

• 在完全填充并释放压力后，对Libersorb 23纳米孔中水的填充度（θ）进行时间分辨测量。
• 在多个时间尺度上分析θ(t)，以识别不同的松弛阶段。
• 计算孔道的排出时间分布函数，以模拟观测到的松弛动力学。
• 采用幂律拟合（θ ∼ t⁻ᵅ）量化不同时间区间内的松弛指数。
• 识别充满孔道的连通团簇为实现长程团簇相互作用的结构框架。
• 将实验测得的θ(t)数据与基于团簇相互作用和孔道连通性的理论预测进行比较。

实验结果

研究问题

• RQ1 在压力释放后，L23-水体系的松弛行为存在哪些不同的阶段？这些阶段如何随时间演变？
• RQ2 为何系统在中间时间区间表现出幂律松弛（α < 0.1），表明其动力学异常缓慢？
• RQ3 受限孔道中液态纳米团簇之间的相互作用如何导致观测到的非指数型松弛行为？
• RQ4 在t > 10⁵ s时，为何出现从缓慢幂律衰减向更快衰减的过渡？
• RQ5 孔道网络结构，特别是无限连通团簇，如何主导系统的松弛行为？

主要发现

• 在T = 277 K（低于T_d = 284 K）时，压力释放后10秒内，填充度θ从1下降至0.8，表明初始阶段松弛迅速。
• 在t ∼ 10⁵ s的时间范围内，θ(t)遵循幂律衰减，幂律指数α < 0.1，表明处于亚稳态非润湿状态的异常缓慢松弛。
• 第二阶段归因于受限于充满孔道的无限连通团簇中的相互作用液态纳米团簇的集体动力学。
• 在t > 10⁵ s时，系统过渡至更快衰减阶段，幂律指数更大，表明亚稳态的衰减。
• 孔道的排出时间分布函数可定量解释观测到的缓慢松弛行为以及向更快衰减的过渡。
• 亚稳态的松弛行为由液态团簇的局域构型及其在无序多孔网络中的长程相互作用所主导。