Entropically driven microphase transitions in mixtures of colloidal rods and spheres
Entropically driven microphase transitions in mixtures of colloidal rods and spheres
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DOI：
10.1038/30700
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发表时间：
1998-05-28
期刊：
影响因子：
64.8
通讯作者：
Fraden, S
中科院分区：
文献类型：
--
作者：
Adams, M;Dogic, Z;Fraden, S
尽管单靠熵就足以产生有序状态的想法在胶体科学中是一个古老的想法(1)，但这个概念仍然是违反直觉的，而且它(通常假设吸引人的相互作用是产生长程有序的相所必需的)，棒和球的相行为已经被实验(1-7)、理论(8，9)和计算机模拟(10)研究。在这里，我们描述了胶体棒状和球状粒子(分别是病毒和聚苯乙烯胶乳或聚氧化乙烯聚合物)混合物在它们像硬粒子(2，3)的条件下的相行为。我们发现了大量的行为：大量分离成富棒相和贫棒相，以及微相分离成各种形态。一个微相由棒层和球层(11)交替组成；在另一个出乎意料的复杂的微相中，球体可逆地组装成柱状物，这些柱状物又填充成晶体阵列。我们的实验，以及之前的理论和计算机模拟(11)表明，这种相态行为是由粒子之间的空间斥力熵驱动的。这种现象可能是非常普遍的，例如也适用于低分子质量的液晶(12)。这种微相分离也可能与两亲性(13)和嵌段共聚物(14)体系有关，与原核生物的生物分离方法和DNA分配(15)有关，与蛋白质结晶(16，17)和复合材料的制造有关。
Although the idea that entropy alone is sufficient to produce an ordered state is an old one in colloid science(1), the notion remains counter-intuitive and it is (often assumed that attractive interactions are necessary to generate phases with long-range order, The phase behaviour for both rods and spheres has been studied experimentally(1-7), theoretically(8,9) and by computer simulations(10). Here we describe the phase behaviour of mixtures of colloidal rodlike and sphere-like particles (respectively viruses and polystyrene latex or polyethylene oxide polymer) under conditions in which they act like hard' particles(2,3). We find a wealth of behaviour: bulk demixing into rod-rich and rod-poor phases and microphase separation into a variety of morphologies. One microphase consists of layers of rods alternating with layers of spheres(11); in another microphase of unanticipated complexity, the spheres reversibly assemble into columns, which in turn pack into a crystalline array. Our experiments, and previous theory and computer simulations(11), suggest that this phase behaviour is entropically driven by steric repulsion between particles. The phenomena are likely to be quite general, applying also for example to low-molecular-mass liquid crystals(12). This kind of microphase separation might also be relevant to systems of amphiphiles(13) and block copolymers(14), to bioseparation methods and DNA partitioning in prokaryotes(15), and to protein crystallization(16,17) and the manufacture of composite materials.