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arXiv 2209.01271cond-mat.soft
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振动颗粒介质中的几何控制相变

Geometry-controlled phase transition in vibrated granular media

René Zuñiga, Germán Varas, Stéphane Job

摘要:

我们报告的实验振动颗粒的动力学约束在一个二维的垂直容器,动机是以下问题:如何得到最大的外部振动,以最大限度地提高内部的混乱(例如,混合颗粒)和搅拌(例如,吸收振动)?颗粒介质类似于经典的热力学系统,其中能量的注入可以通过摇动它们来实现:通过调整振荡的振幅或频率来产生流化。或者,我们探索当另一个特征,容器几何形状,被修改,同时保持恒定的能量注入时会发生什么。我们的方法包括将容器底部修改成V形,以打破内部颗粒排列的对称性。在任何热搅拌下,晶格包含与松散的无定形流体状相共存的紧凑的六方固体状结晶相。我们发现,固体到流体的体积分数和颗粒温度不仅取决于外部振动,但也对由容器的不对称性触发的拓扑缺陷的数量。前者依赖于能量涨落的统计,后者与KTHNY理论描述的二维熔融转变相一致。

英文摘要:

We report experiments on the dynamics of vibrated particles constrained in a two-dimensional vertical container, motivated by the following question: how to get the most out of a given external vibration to maximize internal disorder (e.g. to blend particles) and agitation (e.g. to absorb vibrations)? Granular media are analogs to classical thermodynamic systems, where the injection of energy can be achieved by shaking them: fluidization arises by tuning either the amplitude or the frequency of the oscillations. Alternatively, we explore what happens when another feature, the container geometry, is modified while keeping constant the energy injection. Our method consists in modifying the container base into a V-shape to break the symmetries of the inner particulate arrangement. The lattice contains a compact hexagonal solid-like crystalline phase coexisting with a loose amorphous fluid-like phase, at any thermal agitation. We show that both the solid-to-fluid volume fraction and the granular temperature depend not only on the external vibration but also on the number of topological defects triggered by the asymmetry of the container. The former relies on the statistics of the energy fluctuations and the latter is consistent with a two-dimensional melting transition described by the KTHNY theory.

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