Bauman Moscow State Technical University, 2nd Baumanskaya Street 5, Moscow, Russia, 105005.
Sci Rep. 2023 Feb 16;13(1):2815. doi: 10.1038/s41598-022-26390-w.
Self-diffusion in fluids has been thoroughly studied numerically, but even for simple liquids just a few scaling relationships are known. Relations between diffusion, excitation spectra, and character of the interparticle interactions remain poorly understood. Here, we show that diffusion mobility of particles in simple fluids increases linearly on the liquid branch of the liquid-gas binodal, from the triple point almost up to the critical point. With molecular dynamics simulations, we considered bulk systems of particles interacting via a generalised Lennard-Jones potential, as well as ethane. Using a two-oscillator model for the analysis of excitations, we observed that the mobility (inverse diffusion) coefficient on the liquid-gas binodal increases linearly above the triple point until the dispersion of high-frequency spectra has a solid-like (oscillating) shape. In terms of a separate mode analysis (of longitudinal and transverse modes), this corresponds to crossed modes in the intermediate range of wavenumbers q, between the hydrodynamic regime (small q) and the regime of individual particle motion (large q). The results should be interesting for a broad community in physics and chemistry of fluids, since self-diffusion is among the most fundamental transport phenomena, important for prospective chemical technologies, micro-, nanofluidics, and biotechnologies.
流体中的自扩散已经得到了深入的数值研究，但即使对于简单的液体，也只知道几种标度关系。扩散、激发谱与粒子间相互作用特性之间的关系仍未得到很好的理解。在这里，我们表明，简单流体中粒子的扩散迁移率在线性增加液体-气体分界限的液体分支上，从三相点几乎增加到临界点。我们通过分子动力学模拟，考虑了通过广义 Lennard-Jones 势相互作用的颗粒的体相系统，以及乙烷。通过使用双振荡器模型分析激发，我们观察到，在三相点以上，在高频谱的弥散具有固体状（振荡）形状之前，迁移率（扩散的倒数）系数在线性增加。根据单独的模态分析（纵模和横模），这对应于中间波数 q 范围内的交叉模态，介于流体力学区（小 q）和单个粒子运动区（大 q）之间。由于自扩散是最基本的输运现象之一，对于有前途的化学技术、微纳流体和生物技术都很重要，因此这些结果对于物理学和化学流体领域的广泛社区都应该是有趣的。
