Departamento de Física Teórica de la Materia Condensada, Instituto de Física de la Materia Condensada (IFIMAC), Instituto de Ciencias de Materiales "Nicolás Cabrera", Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, E-28049 Madrid, Spain.
Department of Chemistry, Department of Physics, Institute for the Science and Technology of Materials, Program for Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544, USA.
Soft Matter. 2018 Oct 17;14(40):8205-8218. doi: 10.1039/c8sm01519h.
We generate and study dense positionally and/or orientationally disordered, including jammed, monodisperse packings of hard convex lens-shaped particles (lenses). Relatively dense isotropic fluid configurations of lenses of various aspect ratios are slowly compressed via a Monte Carlo method based procedure. Under this compression protocol, while 'flat' lenses form a nematic fluid phase (where particles are positionally disordered but orientationally ordered) and 'globular' lenses form a plastic solid phase (where particles are positionally ordered but orientationally disordered), 'intermediate', neither 'flat' nor 'globular', lenses do not form either mesophase. In general, a crystal solid phase (where particles are both positionally and orientationally ordered) does not spontaneously form during lengthy numerical simulation runs. In correspondence to those volume fractions at which a transition to the crystal solid phase would occur in equilibrium, a 'downturn' is observed in the inverse compressibility factor versus volume fraction curve beyond which this curve behaves essentially linearly. This allows us to estimate the volume fraction at jamming of the dense non-crystalline packings so generated. These packings are nematic for 'flat' lenses and plastic for 'globular' lenses, while they are robustly isotropic for 'intermediate' lenses, as confirmed by the calculation of the τ order metric, among other quantities. The structure factors S(k) of the corresponding jammed states tend to zero as the wavenumber k goes to zero, indicating they are effectively hyperuniform (i.e., their infinite-wavelength density fluctuations are anomalously suppressed). Among all possible lens shapes, 'intermediate' lenses with aspect ratio around 2/3 are special because they are those that reach the highest volume fractions at jamming while being positionally and orientationally disordered and these volume fractions are as high as those reached by nematic jammed states of 'flat' lenses and plastic jammed states of 'globular' lenses. All of their attributes, taken together, make such 'intermediate' lens packings particularly good glass-forming materials.
我们生成并研究了密集的位置和/或方向无序的，包括堵塞的、单分散的硬凸面透镜状颗粒（透镜）的堆积。通过基于蒙特卡罗方法的程序，我们缓慢压缩具有各种纵横比的透镜的相对密集各向同性流体构型。在这种压缩方案下，“扁平”透镜形成向列流体相（其中颗粒在位置上无序但在方向上有序），“球形”透镜形成塑性固体相（其中颗粒在位置上有序但在方向上无序），而“中间”的、既不是“扁平”也不是“球形”的透镜既不形成中间相也不形成各向同性相。一般来说，在长时间的数值模拟运行中，晶体固体相（其中颗粒在位置和方向上都有序）不会自发形成。在与平衡时会发生晶体固体相转变的那些体积分数相对应的位置，我们观察到反压缩因子与体积分数曲线出现“下降”，在此之后，该曲线基本上呈线性。这使我们能够估计如此生成的密集非晶堆积的堵塞体积分数。对于“扁平”透镜，这些堆积是向列的，对于“球形”透镜，它们是塑性的，而对于“中间”透镜，它们是各向同性的，这一点通过τ阶度量等其他量的计算得到了证实。相应的堵塞状态的结构因子 S(k) 随着波数 k 趋于零而趋于零，这表明它们实际上是超均匀的（即，它们的无穷波长密度涨落异常抑制）。在所有可能的透镜形状中，纵横比约为 2/3 的“中间”透镜是特殊的，因为它们在位置和方向无序的情况下达到堵塞时的最高体积分数，并且这些体积分数与向列堵塞的“扁平”透镜和塑性堵塞的“球形”透镜达到的体积分数一样高。它们所有的属性，综合在一起，使这种“中间”透镜堆积成为特别好的玻璃形成材料。
