Rotational and translational diffusion near the colloidal glass transition

在这个由化学部实验物理化学项目资助的奖项中，Weeks教授和他来自埃默里大学的学生将研究胶体玻璃转变附近的扩散。在常规液体中，粒子和分子经历布朗运动，使它们既平移又旋转。对于给定的粒子（或分子）大小和形状，这些运动的速率具有恒定的比率。例如，液体的粘度增加一倍会减慢这两种运动的速度。然而，在接近玻璃化转变的过冷分子液体中，情况并非如此。间接测量表明，在这些样品中，分子的平移速度比旋转速度快。这表明过冷液体不仅仅是具有大粘度的简单液体，而且扩散是通过根本改变的机制发生的。Weeks教授将使用激光扫描共聚焦显微镜同时直接观察棒状粒子在胶体“过冷流体”中的旋转和平动。胶体悬浮液是由微米大小的固体颗粒在液体中组成的，当颗粒浓度超过临界值时，就会出现玻璃化转变。因为它们可以被直接观察，所以它们是研究这种转变机制的理想系统。共聚焦显微镜将用于观察棒状颗粒和周围胶体颗粒的运动。因此，平移运动和旋转运动可以同时直接测量，从而了解它们之间的关系。科学结果可能有助于设计新型玻璃材料，这可能会影响光纤等技术。威克斯教授每年至少会带领小学生到他的实验室进行一次实地考察。这些学生将研究“黏糊糊的”材料的性质，例如本项目中使用的胶体糊状物。

In this award, funded by the Experimental Physical Chemistry Program of the Chemistry Division, Professor Weeks and his students from Emory University will study diffusion near the colloidal glass transition. In regular liquids, particles and molecules undergo Brownian motion, causing them to both translate and rotate. For a given particle (or molecule) size and shape, the rates of these motions have a constant ratio. For example, doubling the viscosity of the liquid will slow both types of motion by the same factor. However, in supercooled molecular liquids close to the glass transition, this is not the case. Indirect measurements suggest that molecules translate faster than they rotate in these samples. This then suggests that supercooled liquids are not merely simple liquids with large viscosities, but that diffusion takes place by fundamentally changed mechanisms.Professor Weeks will use a laser-scanning confocal microscope to simultaneously and directly observe the rotational and translational dynamics of rod-like particles in a colloidal "supercooled fluid". Colloidal suspensions are composed of micron-sized solid particles in a liquid, and manifest a glass transition as the particle concentration is increased beyond a critical value. Because they can be viewed directly, these are ideal systems for studying the mechanisms of this transition. Confocal microscopy will be used to observe the motion of both the rod-like particles and the surrounding colloidal particles. Thus, both translational and rotational motion can be measured simultaneously and directly, leading to an understanding of how they are related.The scientific results may help in the design new types of glassy materials, which could impact technologies such as fiber optics. Professor Weeks will conduct at least one field trip each year to his laboratory for groups of primary school students. These students will investigate the properties of "squishy" materials such as the colloidal pastes used in this project.