CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China , Hefei, Anhui 230027, China.
Department of Chemistry, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.
ACS Nano. 2015 Dec 22;9(12):12197-204. doi: 10.1021/acsnano.5b06572. Epub 2015 Nov 20.
Evaluation of the tensile/compression limit of a solid under conditions of tension or compression is often performed to provide mechanical properties that are critical for structure design and assessment. Algara-Siller et al. recently demonstrated that when water is constrained between two sheets of graphene, it becomes a two-dimensional (2D) liquid and then is turned into an intriguing monolayer solid with a square pattern under high lateral pressure [ Nature , 2015 , 519 , 443 - 445 ]. From a mechanics point of view, this liquid-to-solid transformation characterizes the compression limit (or metastability limit) of the 2D monolayer water. Here, we perform a simulation study of the compression limit of 2D monolayer, bilayer, and trilayer water constrained in graphene nanocapillaries. At 300 K, a myriad of 2D ice polymorphs (both crystalline-like and amorphous) are formed from the liquid water at different widths of the nanocapillaries, ranging from 6.0 to11.6 Å. For monolayer water, the compression limit is typically a few hundred MPa, while for the bilayer and trilayer water, the compression limit is 1.5 GPa or higher, reflecting the ultrahigh van der Waals pressure within the graphene nanocapillaries. The compression-limit (phase) diagram is obtained at the nanocapillary width versus pressure (h-P) plane, based on the comprehensive molecular dynamics simulations at numerous thermodynamic states as well as on the Clapeyron equation. Interestingly, the compression-limit curves exhibit multiple local minima.
在拉伸或压缩条件下评估固体的拉伸/压缩极限，通常是为了提供对结构设计和评估至关重要的机械性能。Algara-Siller 等人最近表明，当水被限制在两片石墨烯之间时，它会变成二维（2D）液体，然后在高侧向压力下变成具有正方形图案的有趣单层固体[自然，2015 年，519，443-445]。从力学角度来看，这种液-固转变表征了 2D 单层水的压缩极限（或亚稳极限）。在这里，我们对二维单层、双层和三层水在石墨烯纳米管中的压缩极限进行了模拟研究。在 300 K 下，在纳米管不同宽度范围内（6.0 至 11.6 Å），从液态水形成了无数的 2D 冰多晶型体（包括结晶状和无定形）。对于单层水，压缩极限通常为几百兆帕，而对于双层和三层水，压缩极限为 1.5 GPa 或更高，反映了石墨烯纳米管内的超高范德华压力。根据在众多热力学状态下进行的综合分子动力学模拟以及克拉珀龙方程，在纳米管宽度与压力（h-P）平面上获得了压缩极限（相）图。有趣的是，压缩极限曲线表现出多个局部最小值。
