Royall C Patrick, Leunissen Mirjam E, Hynninen Antti-Pekka, Dijkstra Marjolein, van Blaaderen Alfons
Institute of Industrial Science, University of Tokyo, Komaba 4-6-1, Meguro-ku, Tokyo 153-8505, Japan.
J Chem Phys. 2006 Jun 28;124(24):244706. doi: 10.1063/1.2189850.
We studied the phase behavior of charged and sterically stabilized colloids using confocal microscopy in a low polarity solvent (dielectric constant 5.4). Upon increasing the colloid volume fraction we found a transition from a fluid to a body centered cubic crystal at 0.0415+/-0.0005, followed by reentrant melting at 0.1165+/-0.0015. A second crystal of different symmetry, random hexagonal close packed, was formed at a volume fraction around 0.5, similar to that of hard spheres. We attribute the intriguing phase behavior to the particle interactions that depend strongly on volume fraction, mainly due to the changes in the colloid charge. In this low polarity system the colloids acquire charge through ion adsorption. The low ionic strength leads to fewer ions per colloid at elevated volume fractions and consequently a density-dependent colloid charge.
我们使用共聚焦显微镜在低极性溶剂（介电常数5.4）中研究了带电和空间稳定胶体的相行为。随着胶体体积分数的增加，我们发现在0.0415±0.0005时从流体转变为体心立方晶体，随后在0.1165±0.0015时发生再入熔化。在体积分数约为0.5时形成了具有不同对称性的第二种晶体，即随机六方密堆积，这与硬球的情况类似。我们将这种有趣的相行为归因于强烈依赖于体积分数的粒子相互作用，这主要是由于胶体电荷的变化。在这个低极性系统中，胶体通过离子吸附获得电荷。低离子强度导致在较高体积分数下每个胶体的离子较少，因此胶体电荷与密度有关。
