Leoni Fabio, Franzese Giancarlo
Secció de Fisica Estadística i Interdisciplinària-Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, Barcelona 08028, Spain.
Institut de Nanociència i Nanotecnología, Universitat de Barcelona, Av. Joan XXIII S/N, Barcelona 08028, Spain.
Phys Rev E. 2016 Dec;94(6-1):062604. doi: 10.1103/PhysRevE.94.062604. Epub 2016 Dec 13.
We study via molecular-dynamics simulations the thermodynamics of an anomalous fluid confined in a slit pore with one wall structured and attractive and another unstructured and repulsive. We find that the phase diagram of the homogeneous part of the confined fluid is shifted to higher temperatures, densities, and pressures with respect to the bulk, but it can be rescaled on the bulk case. We calculate a moderate increase of mobility of the homogeneous confined fluid that we interpret as a consequence of the layering due to confinement and the collective modes due to long-range correlations. We show that, as in bulk, the confined fluid has structural, diffusion, and density anomalies that order in the waterlike hierarchy, and a liquid-liquid critical point (LLCP). The overall anomalous region moves to higher temperatures, densities, and pressure, and the LLCP displaces to higher temperature compared to bulk. Motivated by experiments, we calculate also the phase diagram not just for the homogeneous part of the confined fluid but for the entire fluid in the pore, and we show that it is shifted toward higher pressures but preserves the thermodynamics, including the LLCP. Because our model has waterlike properties, we argue that in experiments with supercooled water confined in slit pores with a width of >3 nm if hydrophilic and of >1.5 nm if hydrophobic, the existence of the LLCP could be easier to test than in bulk, where it is not directly accessible.
我们通过分子动力学模拟研究了一种异常流体在狭缝孔隙中的热力学性质，该孔隙的一侧壁具有结构化且有吸引力，另一侧壁无结构且具有排斥性。我们发现，受限流体均匀部分的相图相对于本体相，在温度、密度和压力方面都向更高值移动，但可以按本体情况进行重新标度。我们计算出均匀受限流体的迁移率有适度增加，我们将其解释为由于受限导致的分层以及长程相关性引起的集体模式的结果。我们表明，与本体情况一样，受限流体具有结构、扩散和密度异常，这些异常在类似水的层次结构中有序排列，并且存在液 - 液临界点（LLCP）。整体异常区域向更高的温度、密度和压力移动，并且与本体相比，LLCP 向更高温度位移。受实验启发，我们不仅计算了受限流体均匀部分的相图，还计算了孔隙中整个流体的相图，并且我们表明它向更高压力移动，但保留了包括 LLCP 在内的热力学性质。由于我们的模型具有类似水的性质，我们认为在实验中，对于宽度大于 3 nm（如果是亲水性）或大于 1.5 nm（如果是疏水性）的狭缝孔隙中过冷的水，LLCP 的存在可能比在本体中更容易测试，因为在本体中它无法直接探测到。
