Mean square displacements of hydrogen atoms in glass-forming materials and proteins, as reported by incoherent elastic neutron scattering, show kinks in their temperature dependence. This crossover, known as the dynamical transition, connects two approximately linear regimes. It is often assigned to the dynamical freezing of subsets of molecular modes at the point of equality between their corresponding relaxation times and the instrumental observation window. The origin of the dynamical transition in glass-forming glycerol is studied here by extensive molecular dynamics simulations. We find the dynamical transition to occur for both the center of mass translations and the molecular rotations at the same temperature, insensitive to changes of the observation window. Both the translational and rotational dynamics of glycerol show a dynamic crossover from the structural to a secondary relaxation at the temperature of the dynamical transition. A significant and discontinuous increase in the orientational Kirkwood factor and in the dielectric constant is observed in the same range of temperatures. We, however, do not find any indications of a true thermodynamic transition to an ordered low-temperature phase. We therefore suggest that all observed crossovers are dynamic in character. The increase in the dielectric constant is related to the dynamic freezing of dipolar domains on the time-scale of simulations.
The boson peak in structural and orientational glasses of simple alcohols: Specific heat at low temperatures
在这项工作中，我们审查比热实验，我们已经进行了不同的氢键玻璃在过去几年中。具体来说，我们已经测量了一组玻璃醇的低温比热Cp：正常和全氘代乙醇，1-和2-丙醇，和甘油。乙醇表现出非常有趣的多态性，在低温下呈现三种不同的固相：完全有序（单斜）晶体，取向无序（立方）晶体或“取向玻璃”，以及普通结构玻璃。通过测量和比较三个相在玻色子峰2-10 K以及低于1 K的隧穿态范围内的低温比热，我们能够定量地证实“玻璃化行为”不是非晶态固体独有的性质。另一方面，丙醇是最简单的一元醇，具有两种不同的立体异构体（1-丙醇和2-丙醇），这使我们能够直接研究原子的空间重排对玻璃普遍性质的影响。我们已经测量了这两种异构体的比热，发现它们之间有一个值得注意的数量差异。最后，还获得了玻璃态甘油的低温比热数据。在这里，我们提出了一个简单的方法的基础上的软势模型来分析低温比热测量，我们用这种方法的定量比较所有这些数据的玻璃醇和作为一个严格的测试的几个普遍的相关性和标度律在文献中提出的。特别地，我们发现玻色子峰的双折射模型[A. V. Granato，Phys. Rev. Lett. 68（1992）974]很好地解释了Cp/T^3出现最大值时的温度。
Influence of confinement on the orientational phase transitions in the lamellar phase of a block copolymer melt under shear flow
在这项工作中，我们将一些真实系统的影响纳入剪切流下的取向相变理论（M。E. Cates和S. T. Milner，Phys. Rev. Lett. v.62，p.1856（1989）和G. H. Fredrickson，J. Rheol. 38，p.1045（1994））。特别是，我们研究的剪切细胞边界上的层状相的取向的影响。我们预测，在低剪切速率的平行取向似乎是稳定的。我们表明，有一个临界值的剪切速率在平行取向失去其稳定性和垂直的一个出现紧低于亚稳。我们将这种过渡与从波动到平均场行为的交叉相关联。在较低的温度下，平行取向的稳定性恢复。我们发现，随着剪切速率的增加，垂直取向的稳定区域迅速减小。这种行为可能被误解为最近在文献中讨论的额外的垂直到平行的转变。
Structural crossovers of quasi-one-dimensional patchy hard superellipses
Institute for Applied Physics, University of Tübingen（蒂宾根大学应用物理研究所）；Physics Department, Centre for Natural Sciences, University of Pannonia（佩奇大学自然科学中心物理系）
