Suspensions of silica particles grafted with concentrated polymer brush: Effects of graft chain length on brush layer thickness and colloidal crystallization
Suspensions of silica particles grafted with concentrated polymer brush: Effects of graft chain length on brush layer thickness and colloidal crystallization
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DOI：
10.1021/ma071770z
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发表时间：
2007-12-11
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：
Ohno, Kohji;Morinaga, Takashi;Fukuda, Takeshi
我们先前报道了由聚（甲基丙烯酸甲酯）（PMMA）的高密度刷提供并悬浮在PMMA的良溶剂中的单分散二氧化硅颗粒（SiP）在一定浓度范围内形成胶体晶体（Macromolecules 2006，39，1245）。在这里，我们研究了类似的混合颗粒的接枝链长度L-C对它们的流体动力学直径D-h在稀悬浮液和胶体结晶在更浓的悬浮液的影响。SiP的平均半径r（0）为65 rim，SiP表面PMMA接枝物的表面密度σ（0）约为0.7链/nm（2）（约36000链/颗粒）。用改进的Daoud-Cotton型标度模型定性地解释了溶胀刷层的流体动力学厚度h（=D-h/2 - r（0））。也就是说，对于短接枝链，h服从普适关系h[1 +（h/2 r（0））] - L-c σ（1/2）（0），适用于平面和球面上的浓缩聚合物刷，而对于长于临界长度的链，h显示出与该线性关系的正偏差，表明刷层进入半稀释聚合物刷状态。混合颗粒的悬浮液显示出从（无序）流体到完全结晶系统的相变，该系统具有窄的流体/晶体共存制度。随着接枝链长度的增加，结晶临界浓度（熔点）降低，当接枝分子量达到50万时，晶体中最近邻粒子间距D_（dis）接近微米级。在D-h和D-dis之间观察到良好的相关性，使得D-dis =（1.15 +/- 0.05）D-h。共聚焦激光扫描显微镜观察表明，胶体晶体通常包括六方密排（hcp）和面心立方（fcc）晶格排列，随着链长的增加，fcc排列可能会增加。
We previously reported that monodisperse silica particles (SiPs) afforded with a high-density brush of poly(methyl methacrylate) (PMMA) and suspended in a good solvent for PMMA formed a colloidal crystal in a certain concentration range (Macromolecules 2006, 39, 1245). Here we investigated similar hybrid particles with respect to the influence of graft chain length L-c on their hydrodynamic diameter D-h in dilute suspension and on colloidal crystallization in more concentrated suspension. The average radius r(0) of SiPs was 65 rim, and the surface density sigma(0) of PMMA grafts at the SiP surface was about 0.7 chains/nm(2) (about 36 000 chains per particle). The hydrodynamic thickness of the swollen brush layer h (=D-h/2 - r(0)) was qualitatively interpretable by a modified Daoud-Cotton-type scaling model. Namely, for short graft chains, h obeyed the universal relation, h[1 + (h/2r(0))] - L-c sigma(1/2)(0), applicable to concentrated polymer brushes on flat as well as spherical surfaces, and for chains longer than a critical length, h showed positive deviations from this linear relation, indicating the brush layer getting into the semidilute polymer brush regime. Suspensions of the hybrid particles showed a phase transition from a (disordered) fluid to a fully crystallized system with a narrow fluid/crystal coexisting regime. The critical concentration of crystallization (melting point) decreased with increasing graft chain length, and the nearest-neighbor interparticle distance D-dis in the crystal approached to a micrometer scale as the graft molecular weight reached 500 000. Good correlation was observed between D-h and D-dis such that D-dis = (1.15 +/- 0.05)D-h. Confocal laser scanning microscopic observation suggested that the colloidal crystal generally include both hexagonal close-packed (hcp) and face-centered cubic (fcc) lattice arrangements with the fcc arrangement likely to increase with increasing chain length.