水-叔丁醇混合物中波动的微观非均匀性和具有相变样多重异常的平均团簇尺寸的Wenda型发散
Fluctuating micro-heterogeneity in water - tert-butyl alcohol mixtures and lambda-type divergence of the mean cluster size with phase transition-like multiple anomalies
摘要：
水-叔丁醇（TBA）二元混合物表现出大量的热力学和动力学异常。这些异常现象是在令人惊讶的低TBA摩尔分数下观察到的，使用$x_{\text{TBA}} \approx 0.03 - 0.07$。我们在这里证明，异常的起源在于由于TBA分子的自聚集而发生的局部结构变化。我们观察到TBA分子在$x_{\text{TBA}} \approx 0.05$处的逾渗转变。我们注意到，“岛”的TBA集群形成甚至低于这个摩尔分数，而一个大的跨越集群出现以上的摩尔分数。在这个渗流阈值，我们观察到的最大的TBA集群的大小的波动，让人想起一个临界点的一个EQUIDDA型的分歧。此外，水的结构也受到TBA分子聚集的干扰，尽管很弱。水的四面体序参量呈单调减小的趋势，而偶极矩关联呈现弱的非线性。有趣的是，水分子本身在较高的TBA浓度下表现出反向渗滤转变，$x_{\text{TBA}} \approx 0.45$，其中大的跨越水簇现在分裂成小簇。这是伴随着最大的水集群的大小波动的显着分歧。这第二次转变引起了周围的另一组异常现象。这两种逾渗转变都可以看作是Janus效应在小分子水平上的表现。
英文摘要：
Water - tert-butyl alcohol (TBA) binary mixture exhibits a large number of thermodynamic and dynamic anomalies. These anomalies are observed at surprisingly low TBA mole fraction, with $x_{\text{TBA}} \approx 0.03 - 0.07$. We demonstrate here that the origin of the anomalies lies in the local structural changes that occur due to self-aggregation of TBA molecules. We observe a percolation transition of the TBA molecules at $x_{\text{TBA}} \approx 0.05$. We note that "islands" of TBA clusters form even below this mole fraction, while a large spanning cluster emerges above that mole fraction. At this percolation threshold, we observe a lambda-type divergence in the fluctuation of the size of the largest TBA cluster, reminiscent of a critical point. Alongside, the structure of water is also perturbed, albeit weakly, by the aggregation of TBA molecules. There is a monotonic decrease in the tetrahedral order parameter of water, while the dipole moment correlation shows a weak non-linearity. Interestingly, water molecules themselves exhibit a reverse percolation transition at higher TBA concentration, $x_{\text{TBA}} \approx 0.45$, where large spanning water clusters now break-up into small clusters. This is accompanied by significant divergence of the fluctuations in the size of largest water cluster. This second transition gives rise to another set of anomalies around. Both the percolation transitions can be regarded as manifestations of Janus effect at small molecular level.
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