Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
ACS Nano. 2018 Jan 23;12(1):448-454. doi: 10.1021/acsnano.7b06805. Epub 2018 Jan 3.
Flexible nanoscale confinement is critical to understanding the role that bending fluctuations play on biological processes where soft interfaces are ubiquitous or to exploit confinement effects in engineered systems where inherently flexible 2D materials are pervasively employed. Here, using molecular dynamics simulations, we compare the phase behavior of water confined between flexible and rigid graphene sheets as a function of the in-plane density, ρ. We find that both cases show commensurate mono-, bi-, and trilayered states; however, the water phase in those states and the transitions between them are qualitatively different for the rigid and flexible cases. The rigid systems exhibit discontinuous transitions between an (n)-layer and an (n+1)-layer state at particular values of ρ, whereas under flexible confinement, the graphene sheets bend to accommodate an (n)-layer and an (n+1)-layer state coexisting in equilibrium at the same density. We show that the flexible walls introduce a very different sequence of ice phases and their phase coexistence with vapor and liquid phases than that observed with rigid walls. We discuss the applicability of these results to real experimental systems to shed light on the role of flexible confinement and its interplay with commensurability effects.
灵活的纳米级限制对于理解弯曲波动在普遍存在软界面的生物过程中所起的作用至关重要，或者对于利用在工程系统中普遍使用的固有柔性 2D 材料的限制效应也至关重要。在这里，我们使用分子动力学模拟，比较了柔性和刚性石墨烯片之间受限水的相行为作为面内密度 ρ 的函数。我们发现这两种情况都显示了共格的单、双和三层状态；然而，对于刚性和柔性情况，这些状态中的水相和它们之间的转变在性质上是不同的。刚性系统在特定的 ρ 值下表现出从（n）层到（n+1）层状态的不连续转变，而在柔性限制下，石墨烯片弯曲以适应在相同密度下共存的（n）层和（n+1）层状态。我们表明，柔性壁引入了与刚性壁观察到的非常不同的冰相序列及其与蒸气和液相的相共存。我们讨论了这些结果在实际实验系统中的适用性，以阐明灵活限制及其与共格效应相互作用的作用。
