Disorder in Crystals and Mesophases

本项目的目标是探索线性大分子和小分子模型化合物通过构象、大幅度运动在晶态和中间相态中引入的无序。更好地理解这一主题将使我们能够更好地管理诸如通过退火改善材料性能、拉深和轧制时的大变形以及设计具有特定性能的新型聚合物材料等重要的工艺过程。该项目中使用的核心技术是用于评估无序度(熵)的热分析。多年来开发的一种特殊的高级热分析系统(ATAS)允许将全有序固体的热性质建立为仅限振动的参考态，以及完全无序的固体(玻璃态)和液体参考态。偏离这些参考态的情况可以用移动无序(中间相)或刚性无序(中间相玻璃或刚性无定形分数)来解释。在微观水平上，用固体核磁共振、X射线衍射、中子散射、光学显微镜和原子力显微镜对无序和运动进行了详细分析。实验结果与在超级计算机上进行的分子动力学模拟进行了比较。要分析的典型材料有：尼龙和蛋白质、硬链聚合物、部分和完全氟化的短链和长链分子、四烷基铵盐和中间相聚合物。

The objective of this project is to explore disorder introduced in crystalline and mesophase states of linear macromolecules and small molecule model compounds by conformational, large-amplitude motion. Better understanding of this topic will enable us to better manage such important technological processes as the improvement of materials performance by annealing, large-scale deformation on drawing and rolling, and the design of new polymeric materials with specific properties. The central technique used in this project is the thermal analysis for evaluation of the degree of disorder (entropy). A special Advanced THermal Analysis System (ATHAS), developed over the years, permits the establishment of the thermal properties of fully ordered solids as a vibration-only reference state, as well as fully disordered solid (glassy) and liquid reference states. The deviations from these references states are interpreted in terms of mobile disorder (mesophases) or rigid disorder (mesophase glasses or rigid amorphous fraction). On a microscopic level the disorder and motion are then analyzed in detail by solid state NMR, X-ray diffraction, neutron scattering, optical and atomic force microscopy. The experimental results are compared to molecular dynamics simulations carried out on supercomputers. Typical materials to be analyzed are: nylons and proteins, stiff-chain polymers, partially and fully fluorinated short-chain and long-chain molecules, tetraalkylammonium salts, and mesophase polymers.