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arXiv 2202.06786cond-mat.soft
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流体中驱动相关摩擦的分子起源

Molecular origin of driving-dependent friction in fluids

Matthias Post, Steffen Wolf, Gerhard Stock

摘要:

流体的摩擦系数在外部驱动增加时可能成为速度的函数。这种非牛顿行为具有普遍的理论意义以及很大的实际重要性,例如,用于润滑剂的设计。虽然在大规模的散装液体的原子模拟中观察到了这种效应,但其理论公式和微观起源还没有得到很好的理解。在这里,我们使用耗散校正有针对性的分子动力学,拉开两个标记的液体分子在周围的分子的存在下,并通过广义朗之万方程分析这个非平衡过程。该方法是基于二阶累积展开的Jarzynski的身份,这是有效的流体,因此允许一个精确的计算的摩擦配置文件以及底层的内存内核。我们表明,流体中的速度依赖性摩擦的结果从一个复杂的相互作用的近阶结构效应和非马尔可夫行为的摩擦记忆内核。对于复杂的流体,如模型润滑剂\alkane,记忆内核表现出拉伸指数长时间衰减,这反映了系统的时间尺度的众多。

英文摘要:

The friction coefficient of fluids may become a function of the velocity at increased external driving. This non-Newtonian behavior is of general theoretical interest as well as of great practical importance, e.g., for the design of lubricants. While the effect has been observed in large-scale atomistic simulations of bulk liquids, its theoretical formulation and microscopic origin is not well understood. Here we use dissipation-corrected targeted molecular dynamics, which pulls apart two tagged liquid molecules in the presence of surrounding molecules and analyzes this nonequilibrium process via a generalized Langevin equation. The approach is based on a second-order cumulant expansion of Jarzynski's identity, which is shown to be valid for fluids and therefore allows for an exact computation of the friction profile as well of the underlying memory kernel. We show that velocity-dependent friction in fluids results from an intricate interplay of near-order structural effects and the non-Markovian behavior of the friction memory kernel. For complex fluids such as the model lubricant \alkane, the memory kernel exhibits a stretched-exponential long-time decay, which reflects the multitude of timescales of the system.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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