Jamming in Model Supercooled Liquids and Athermal Systems

本基金支持对无序系统性质的理论和计算研究。特别是对干扰的概念进行了研究。许多没有淬火失序的系统会发生卡塞，即在失序状态下产生屈服应力或不可测量的长应力松弛时间。这些系统包括过冷液体、胶体悬浮液、颗粒材料、乳液和泡沫。最近有人提出，干扰的发生可能会导致某种程度的普遍性。这就是干扰的概念。具体地说，有人建议不同的系统在被干扰时应该表现出相似的行为，并且每个系统都有一个干扰相位图。干扰的概念将在两个非常不同的系统上进行数值模拟，这两个系统都表现出向约束动力学的过渡。第一种是静态热系统，即二元Lennard-Jones混合物。当温度降低到玻璃化转变时，这个模型已被证明会堵塞。第二个要研究的系统是一个驱动的非热系统，当剪切应力降低到屈服应力或当颗粒密度高于紧密堆积时，该系统被证明会堵塞。提出的研究的一个目标是利用干扰的想法，通过应用颗粒材料（即力链）到过冷液体的最新想法来获得对玻璃化转变的新见解。我们还将通过计算二元Lennard-Jones混合物的完全干扰相图来测试干扰的想法。最后，我们将测试剪切引起的波动是否可以通过增强的有效温度来描述二元Lennard-Jones混合物。有效温度的概念已经被广泛用于描述未堵塞的颗粒材料，需要仔细研究。至少，我们将更多地了解两个有趣的系统（过冷液体和剪切非热填料）的行为，即使我们发现它们之间的联系只是表面的。然而，如果干扰的概念是正确的，它将是非常强大的，因为从一个系统衍生出来的想法将适用于另一个系统。认识到可以在更广泛的框架内看待不同的系统，这在过去给许多领域带来了革命性的变化。探索干扰的途径是重要的，因为它可能导致对长期未解决的问题，如玻璃化转变的新的和更深的理解。该基金支持对无序系统性质的理论和计算研究。特别是对干扰的概念进行了研究。堵塞通常以交通堵塞的形式发生在我们大多数人身上。当太多的车辆试图通过一条受限制的道路时，顺畅的交通就会停止或堵塞。许多由许多粒子组成的物理系统也会发生堵塞，即在无序状态下产生屈服应力或不可测量的长应力松弛时间。这些系统包括过冷液体、胶体悬浮液、颗粒材料、乳液和泡沫。最近有人提出，干扰的开始可能导致这些不同系统之间某种程度的普遍性。这就是干扰的概念。具体地说，有人建议不同的系统在被干扰时应该表现出相似的行为，并且每个系统都有一个干扰相位图。在这项研究中，干扰的概念将通过两个非常不同的系统的数值模拟来探讨，这两个系统都表现出向约束动力学的过渡。＊＊＊

0087349LiuThis grant supports theoretical and computational research on the properties of disordered systems. In particular, research will be done on the concept of jamming. Many systems with no quenched disorder can jam, i.e., develop a yield stress or an immeasurably long stress relaxation time in a disordered state. These systems include supercooled liquids, colloidal suspensions, granular materials, emulsions and foams. It has recently been suggested that the onset of jamming might lead to some degree of universality. This is the concept of jamming. Specifically, it has been suggested that different systems should show similar behavior as they jam, and that each system has a jamming phase diagram.The concept of jamming will be explored using numerical simulations on two very different systems that both exhibit transitions to constrained dynamics. The first is a quiescent thermal system, namely a binary Lennard-Jones mixture. This model has been shown to jam as the temperature is lowered to the glass transition. The second system to be studied is a driven, athermal system that has been shown to jam as the shear stress is lowered to the yield stress or as the density of particles is raised above close-packing.One objective of the proposed research is to exploit the idea of jamming to gain new insight into the glass transition by applying recent ideas from granular materials (namely force chains) to supercooled liquids. We will also test the idea of jamming by calculating the complete jamming phase diagram for a binary Lennard-Jones mixture. Finally, we will test whether shear-induced fluctuations can be described by an enhanced effective temperature in binary Lennard-Jones mixtures. The idea of an effective temperature is already widely used to describe unjammed granular materials and needs to be examined carefully.At a minimum, we will learn much more about the behavior of two intriguing systems (supercooled liquids and sheared athermal packings), even if we discover that their connection is only superficial. If the concept of jamming is correct, however, it will be extremely powerful because ideas derived from one system will be applicable to another. The recognition that different systems can be viewed within a broader framework has revolutionalized a number of fields in the past. It is important to explore the avenue of jamming because it may lead to new and deeper understanding of long unsolved problems such as the glass transition.%%% This grant supports theoretical and computational research on the properties of disordered systems. In particular, research will be done on the concept of jamming. Jamming commonly occurs to most of us in the form of traffic jams. As too many vehicles try to pass through a constrained path, the smooth flow of traffic becomes stopped or jammed. Many physical systems comprised of many particles can also jam, i.e., develop a yield stress or an immeasurably long stress relaxation time in a disordered state. These systems include supercooled liquids, colloidal suspensions, granular materials, emulsions and foams. It has recently been suggested that the onset of jamming might lead to some degree of universality among these diverse systems. This is the concept of jamming. Specifically, it has been suggested that different systems should show similar behavior as they jam, and that each system has a jamming phase diagram. In this research the concept of jamming will be explored using numerical simulations on two very different systems that both exhibit transitions to constrained dynamics. ***