Structural analysis of "Semisoft" colloidal crystals by confocal laser scanning microscopy
Structural analysis of "Semisoft" colloidal crystals by confocal laser scanning microscopy
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DOI：
10.1021/ma7028665
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发表时间：
2008-05-27
期刊：
影响因子：
5.5
通讯作者：
Fukuda, Takeshi
中科院分区：
文献类型：
--
作者：
Morinaga, Takashi;Ohno, Kohji;Fukuda, Takeshi
在接枝密度近似固定在一个高值的情况下，研究了由球形颗粒上的聚合刷（CPBs）之间的空间或非体积相互作用形成的半软胶体晶体的晶体结构与接枝链长度的关系。基于Stober方法，采用溶胶-凝胶化学方法合成了罗丹明标记的低多分散二氧化硅颗粒（平均直径590 nm），然后通过表面引发原子转移自由基聚合将其接枝到定义明确的聚甲基丙烯酸甲酯高密度刷壳上。用共聚焦激光扫描显微镜在荧光模式下直接（原位）观察了这些杂化颗粒在液体悬浮液中形成的胶体晶体的内部结构。在所有情况下，晶体结构均为密排型，晶体中最近邻颗粒间距离随接枝链长度的增加而增加。晶体由二维六边形密排平面组成，并以六边形密排（hcp）和面心立方（fcc）晶格排列的统计顺序堆叠。在相对较短的接枝链区域，发现fcc叠加的概率a约为0.59，在相对较长的接枝链区域，发现fcc叠加的概率a基本等于1.0（完美fcc），中间过渡区相当窄，α随链长增加而急剧增加。这种晶体结构从几乎随机堆叠到fcc排列的转变归因于接枝链构象的质变，因此伴随着先前提到的聚合物层有效接枝密度的cpb到sdpb（半稀释聚合物刷）交叉的粒子间电位曲线（Ohno等）。高分子学报，2007,33(4):344 - 344。这些结果首次在实验上表明，随着相互作用的范围变长，fcc叠加的流行程度越来越高。因此，通过简单地改变接枝链长度，cpb提供的杂化颗粒的半软胶体晶体可以覆盖典型硬和软胶体晶体之间的大范围结晶浓度和颗粒间电位。
Semisoft colloidal crystals, which are formed by the work of steric or excluded-volume interactions among the concentrated polymer brushes (CPBs) afforded on spherical particles, were studied with respect to their crystalline structure as a function of graft chain length, while the graft density was approximately fixed at a high value. Rhodamine-labeled, low-polydispersity silica particles (average diameter 590 nm) were synthesized using the sol-gel chemistry based on the Stober method and then grafted with a shell of well-defined poly(methyl methacrylate) high-density brush by surface-initiated atom transfer radical polymerization. The internal structure of colloidal crystals formed in a liquid suspension of those hybrid particles was directly (in situ) observed by confocal laser scanning microscopy in fluorescence mode. The crystalline structure Was of close-packed type in all cases, and the nearest-neighbor interparticle distance in the crystal increased with increasing graft chain length. The crystals consisted of two-dimensional hexagonal close-packed planes which are stacked in a statistical sequence of hexagonal close-packed (hcp) and face-centered cubic (fcc) lattice arrangements. The probability a of finding a fcc stacking was about 0.59 in a region of relatively short graft chains and substantially equal to 1.0 (perfect fcc) in a region of relatively long graft chains, exhibiting a rather narrow intermediate transition region, where alpha steeply increased with increasing chain length. This transition of crystalline structure from a nearly random stacking to the fcc arrangement was ascribed to a qualitative change in graft chain conformation and hence interparticle potential curve accompanying the previously noted CPB-to-SDPB (semidilute polymer brush) crossover in the effective graft density of the polymer layer (Ohno et al. Macromolecules 2007, 40, 9143). These results are the first to experimentally show a greater prevalence of fcc stacking as the interaction becomes of longer range. Semisoft colloidal crystals of CPB-afforded hybrid particles can thus cover, by simply changing the graft chain length, a wide range of crystallization concentrations and interparticle potentials between those of typical hard and soft colloidal crystals.