Formation of nematic liquid crystals of sterically stabilized layered double hydroxide platelets
Formation of nematic liquid crystals of sterically stabilized layered double hydroxide platelets
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DOI：
10.1021/jp803114v
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发表时间：
2008-08-21
影响因子：
3.3
通讯作者：
Lekkerkerker, Henk N. W.
中科院分区：
文献类型：
--
作者：
Mourad, Maurice C. D.;Devid, Edwin J.;Lekkerkerker, Henk N. W.
以硝酸镁和硝酸铝为原料，在pH 11~12范围内，按两种不同的镁铝比，用共沉淀法制备了层状双氢氧化物水滑石胶体小片。在水热处理过程中，通过改变温度和离子强度，将血小板定制为不同的大小和长宽比。将氨基修饰的聚异丁烯分子通过一种方便的冷冻干燥新方法嫁接到血小板上。制备了尺寸最大、长径比最大的甲苯有机分散体。用这种方法制备的胶体分散体在几天内就出现了超过极限浓度的各向同性-向列型相变。确定了相变处的数密度和两相区的宽度，并与理论进行了比较。用偏光显微镜分析了向列型液滴(类蛋卷)和各向同性-向列型界面上的血小板取向。观察到，在各向同性-向列相分离的极限浓度以下的样品中，沉积诱导了向列层。未接枝粒子的初始水悬浮液中没有观察到向列相。
Colloidal platelets of hydrotalcite, a layered double hydroxide, have been prepared by coprecipitation at pH 11 - 12 of magnesium nitrate and aluminurn nitrate at two different magnesium to aluminum ratios. Changing the temperature and ionic strength during hydrothermal treatment, the platelets were tailored to different sizes and aspect ratios. Amino-modified polyisobutylene molecules were grafted onto the platelets following a convenient new route involving freeze-drying. Organic dispersions in toluene were prepared of the particles with the largest size and highest aspect ratio. The colloidal dispersions prepared in this way showed isotropic-nematic phase transitions above a limiting concentration in a matter of days. The number density at the transition and the width of the biphasic region were determined and compared to theory. The orientation of the platelets in nematic droplets (tactoids) and at the isotropic-nematic interface were analyzed by polarization microscopy. It was observed that sedimentation induces a nematic layer in samples that are below the limiting concentration for isotropic-nematic phase separation. No nematic phase was observed in the initial aqueous suspensions of the ungrafted particles.