合成与盘状磷酸盐锆剥落获取胶体液晶
Summary
A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.
Abstract
Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2·H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.
Introduction
盘状胶体粘土，沥青质，红细胞，和珍珠层的形式自然丰富。一系列在许多工程系统的应用，包括聚合物纳米复合材料1，仿生材料，功能性膜2，盘状液晶研究3和皮克林乳化稳定剂4是基于盘状胶体纳米盘开发。与均匀性和低的多分散性纳米盘是研究阶段和液晶的转换重要。磷酸锆（的ZrP）是一种合成的纳米盘具有良好有序的层状结构和可控纵横比（厚度比直径）。因此，不同的合成的ZrP的探索有助于建立盘状液晶体系的基本认识。
的ZrP的结构通过Clearfield的和Stynes 于1964年5阐明。对于的ZrP，热液的层状结晶的合成和回流方法通常采用6,7-。水热法给出了大小为400到25％6内1500纳米和多分散性良好的控制，而回流法给出相同的持续时间的时间较小的晶体。微波加热已被证明是纳米材料8的合成有前途的方法。但是，也有根据微波辅助路线描述的ZrP的合成没有说明书。在大小，纵横比，并通过水热法晶体生长机制的有效控制系统是我们小组6的研究。
的ZrP可以容易地剥离成在水性悬浮液的单层，并且剥离的ZrP已经确立作为液晶材料在程的组3,9-13。到目前为止，剥离的ZrP纳米盘具有各种直径，说不同的长宽比，已研究得出结论，较大的ZrP有我（各向同性）-N（向列）过渡在较低CON中心定位比较小的ZrP 3。上向列型液晶相的形成的多分散性3，盐9和温度10,11-效果也已被考虑。此外，其他的阶段，如思迈特液晶相，已研究以及13,14。
在本文中，我们将演示实验实现这样的胶体的ZrP纳米盘悬挂。层状的ZrP的结晶通过不同的方法合成，然后在含水介质中被剥离，以获得单层纳米盘。最后，我们显示由该系统表现出液晶相转变。这些磁盘的一个值得注意的方面是它们的高度各向异性性质的厚径比为0.0007的范围内，以0.05取决于磁盘3的尺寸。高度各向异性的单层纳米盘建立一个模型系统来研究纳米盘的悬浮液的相变。
Protocol
Representative Results
Discussion
回流方法是使α-的ZrP较小大小均匀的直径和厚度一个很好的选择。类似于水热法，回流法是通过准备时间的限制。在一般情况下，它需要的晶体生长更长的时间。
用于回流法需要较长的反应时间可能导致具有较大尺寸纳米盘。剥离纳米盘的平均尺寸通过动态光散射（DLS）测得的。在这项研究中，已剥离的ZrP纳米盘的尺寸为1021.5 nm的19.6％的多分散性，用7.0％多分散289.8纳米，?…
Divulgations
The authors have nothing to disclose.
Acknowledgements
This work is partially supported by NSF (DMR-1006870) and NASA (NASA-NNX13AQ60G). X. Z. Wang acknowledges support from the Mary Kay O’Connor Process Safety Center (MKOPSC) at Texas A&M University. We also thank Min Shuai for her guidance.
Materials
| Material | |||
| Zirconyl Chloride Octahydrate | Fischer Scientific (Acros Organics) | AC20837-5000 | 98% + |
| o-Phosphoric Acid | Fischer Scientific | A242-1 | >= 85 % |
| Tetra Butyl Ammonium Hydroxide | Acros Organics (Acros Organics) | AC176610025 | 40% wt. (1.5M) |
| Name | Company | Catalog Number | Comments |
| Equipment | |||
| Reaction Oven | Fischer Scientific | CL2 centrifuge | Isotemperature Oven (Temperature Upto 350 C) |
| Centrifuge | Thermo Scientific | Not Available | Rotation Speed : 100 – 4000 rpm |
| Microwave Reactor | CEM Corporation | Discover and Explorer SP | Temp. Upto 300oC, Power upto 300W, Pressure upto 30bar |
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