Department of Physics, Harvard University, Cambridge, MA 02138, USA.
Science. 2010 Jan 29;327(5965):560-3. doi: 10.1126/science.1181263.
The study of clusters has provided a tangible link between local geometry and bulk condensed matter, but experiments have not yet systematically explored the thermodynamics of the smallest clusters. Here we present experimental measurements of the structures and free energies of colloidal clusters in which the particles act as hard spheres with short-range attractions. We found that highly symmetric clusters are strongly suppressed by rotational entropy, whereas the most stable clusters have anharmonic vibrational modes or extra bonds. Many of these clusters are subsets of close-packed lattices. As the number of particles increases from 6 to 10, we observe the emergence of a complex free-energy landscape with a small number of ground states and many local minima.
团簇的研究为局部几何形状和凝聚态物质之间提供了一个切实的联系，但实验尚未系统地探索最小团簇的热力学。在这里，我们展示了胶体团簇的结构和自由能的实验测量结果，其中粒子表现为具有短程吸引力的硬球体。我们发现，高度对称的团簇受到旋转熵的强烈抑制，而最稳定的团簇具有非谐振动模式或额外的键。这些团簇中有许多是密堆积晶格的子集。随着粒子数从 6 增加到 10，我们观察到具有少量基态和许多局部最小值的复杂自由能景观的出现。
