羧基化纤维素溶致液晶行为的研究及其复合材料的制备

发布时间：2018-03-21 01:20

本文选题：TEMPO氧化体系　切入点：胆甾型液晶　出处：《青岛科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：基于可再生资源的纳米材料因其广阔的应用前景而引起了人们越来越多的兴趣,天然纳米材料所具有的生态优势、加工性能和光子晶体特性,对于多功能纳米材料的发展意义重大。纤维素是一类来源十分广泛的可持续发展材料,通过改性处理得到的纳米纤维素可以用于各种新型材料的制备。2,2,6,6-四甲基哌啶-1-氧自由基(2,2,6,6-tetramethylpiperidine-1-oxyl radical,TEMPO)-NaBr-NaClO催化氧化体系是一种对纤维素进行氧化改性制备纤维素纳米晶体(cellulose nanocrystals,CNCs)的有效方法,在温和的反应条件下,可以有效地选择性氧化CNCs表面C6位伯羟基为羧基,实现对其表面的功能化。本论文中,采用盐酸水解和TEMPO体系氧化的方法处理棉花纤维素,制备了TEMPO体系氧化后的棉花纤维素纳米晶体(TEMPO-oxidized cotton cellulose nanocrystals,c-TOCNs)及其溶致胆甾型液晶(chiral nematic liquid crystals,N*-LCs)。通过调节c-TOCNs悬浮液的浓度,利用偏光显微镜技术(polarizing optical microscopy,POM)系统地研究了其形成液晶(liquid crystals,LCs)的临界浓度。研究结果表明,c-TOCNs悬浮液形成LCs的临界浓度是4.1 wt%,并首次成功地在9.0 wt%的浓度下观察到了N*-LCs的特征结构指纹织构。与此同时,将TEMPO氧化体系得到的溶致N*-LCs的液晶行为与硫酸水解体系进行了对比,并讨论了纳米晶体尺寸和表面电荷密度这两个因素对LCs形成的临界浓度和螺距(helical pitch,P)大小的影响。通过向c-TOCNs悬浮液中添加不同浓度NaCl溶液以改变其离子强度的方法,探究了离子强度对羧基化纤维素溶致N*-LCs液晶行为的影响。研究结果表明随着悬浮液中NaCl浓度的增大,各项异性相中有序畴的范围变少,且P减小。这是由于NaCl的加入对c-TOCNs的表面电荷产生了屏蔽作用,导致双电层厚度减小,带电纳米棒的有效直径和表观体积下降,使得c-TOCNs间的静电排斥作用减弱,从而减小了P。聚苯胺(polyaniline,PANI)具有优异的导电性能,将其与纤维素复合可以制备新型导电纳米复合材料。本论文中,从海鞘中提取出纤维素,并通过TEMPO体系氧化法制备了海鞘纤维素纳米晶体(TEMPO-oxidized tunicate cellulose nanocrystals,t-TOCNs)。然后以t-TOCNs为模板,利用原位聚合法,成功地制备了PANI/t-TOCNs复合材料。羧酸根的引入很好地提高了t-TOCNs的分散性,并且提供了较多的氢键位点,这些氢键位点吸引苯胺单体生长,从而形成导电涂覆。PANI和t-TOCNs之间主要是通过氢键作用结合在一起,PANI的加工性能得到了较好改善。制备的PANI/t-TOCNs复合材料具有良好的导电性,电导率可以达到0.26 S·cm-1,表现出半导体的性质,随着An/OH的比例增大,导电性增强,将在超级电容器、传感器等领域有广阔应用。
[Abstract]:Nanomaterials based on renewable resources have attracted more and more interest due to their wide application prospects. Natural nanomaterials have ecological advantages, processing properties and photonic crystal properties. For the development of multifunctional nanomaterials. Cellulose is a class of sustainable development materials from a wide range of sources. The modified nano-cellulose can be used in the preparation of various new materials. The catalytic oxidation system of 6-tetramethylpiperidine-1-oxyl radical TEMPO- NaBr-NaClO is an effective method for the preparation of cellulose nanocrystalline CNCsby oxidation modification. Under mild reaction conditions, the surface of CNCs can be effectively selectively oxidized by C _ 6 hydroxyl group as carboxyl group. In this paper, hydrochloric acid hydrolysis and TEMPO system oxidation were used to treat cotton cellulose. The cotton cellulose nanocrystalline (TEMPO-oxidized cotton cellulose nanocrystalsc TOCNs) and its lyotropic cholesteric liquid crystal, chiral nematic liquid crystalsn, were prepared by adjusting the concentration of c-TOCNs suspension. The critical concentration of liquid crystal crystals formed by polarizing optical microscopy (POM) has been systematically studied. The results show that the critical concentration of c TOCNs to form LCs is 4. 1 wtlong, and N- LCs have been successfully observed for the first time at a concentration of 9. 0 wt%. At the same time, The liquid crystal behavior of lysogenic Na-LCs obtained by TEMPO oxidation system was compared with that of sulfuric acid hydrolysis system. The effects of nanocrystalline size and surface charge density on the critical concentration of LCs formation and the size of helical pitch-P were discussed. The method of changing the ionic strength of c-TOCNs suspension by adding different concentrations of NaCl solution was discussed. The effect of ionic strength on the liquid crystalline behavior of Na-LCs induced by carboxylated cellulose was investigated. The results showed that the range of ordered domains in different heterosexual phases decreased with the increase of NaCl concentration in the suspension. The decrease of P is due to the shielding effect of NaCl on the surface charge of c-TOCNs, which results in the decrease of the thickness of double layer, the decrease of effective diameter and apparent volume of charged nanorods, and the weakening of electrostatic repulsion between c-TOCNs. Therefore, P.Polyaniline polyaniline (PANI) has excellent electrical conductivity. A new type of conductive nanocomposites can be prepared by combining it with cellulose. In this paper, cellulose was extracted from sea sheath. TEMPO system oxidation method was used to prepare tunicate cellulose nanocrystalst-TOCNs, and then PANI/t-TOCNs composites were prepared by in situ polymerization with t-TOCNs as template. The dispersity of t-TOCNs was improved by the introduction of carboxylic acid. And it provides a lot of hydrogen bonding sites that attract aniline monomers to grow. As a result, the processing properties of the conductive coating. Pani and t-TOCNs are mainly combined by hydrogen bonding. The prepared PANI/t-TOCNs composites have good electrical conductivity and the electrical conductivity can reach 0.26 S 路cm-1, which shows the properties of semiconductors. As the proportion of An/OH increases and conductivity increases, it will be widely used in supercapacitors, sensors and other fields.
【学位授予单位】：青岛科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O636.11;TB332

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