【作者】 刘秧生；

【导师】 官建国；

【作者基本信息】 武汉理工大学 ， 材料学， 2010， 博士

【摘要】 电流变液是一种由微、纳米介电颗粒分散在绝缘液体中组成的智能流体,其流变性能在外电场作用下能快速、可逆地出现几个数量级的变化。这种奇异的特性使得电流变液在诸如减振器、离合器、控制阀等机电转换装置方面具有广阔的应用前景。然而,根据介电极化理论设计和制备的传统型电流变液存在剪切应力较低,难以满足工业实际应用要求的缺点。2003年,温维佳等人首次发现用尿素包覆的草酸氧钛钡(BTO)纳米粒子能够产生巨电流变效应,解决了长期以来电流变液剪切应力较低的历史难题。他们认为巨电流变效应的产生是由包覆在纳米粒子表面的尿素薄层界面效应引起的。虽然极性的尿素小分子容易分解的缺点限制了这类巨电流变液的实际应用,但是通过改善粒子界面性质增强材料电流变性能的方法为制备高性能的电流变液提供了一种新颖的设计思路。为此,本文通过表面修饰、形貌控制和核壳结构设计等方法改善BTO粒子的界面特性,同时避免极性分子分解给材料电流变性能带来的负面影响,以期达到提高材料电流变性能的目的。在本文研究中,分别制备了微量聚苯胺(PAn)修饰BTO复合粒子、纳米层状结构的铬掺杂草酸氧钛钡(BCTO)粒子、二氧化硅/草酸氧钛钡(SiO2/BTO)核壳复合粒子等系列电流变材料,通过X射线衍射、红外光谱、扫描电镜、热重分析等方法对这些粒子的结构进行了表征。并将上述材料与甲基硅油组成电流变液,研究它们电流变性能和介电性能的变化规律。本论文的主要研究工作包括以下几个方面：1、采用原位氧化苯胺的方法制备出微量PAn修饰的BTO复合粒子,红外光谱和热重分析表明苯胺被氧化成PAn并很好地修饰在BTO粒子表面,同时减小了材料对水分子的吸附。随着PAn修饰量的增加,复合粒子与硅油之间的接触角减小,浸润性增强；同时复合粒子的电流变性能出现先增大,后降低的变化规律。在PAn修饰量为1.7%(An/BTO=1.7mol%)时,复合粒子表现出最佳的电流变性能,其剪切应力达到54.5 kPa (E=3.5kV/mm),为纯BTO粒子电流变液的3.3倍。1.7% PAn/BTO复合粒子的动态剪切应力和电流变效率均比纯BTO粒子有所提高。介电测试结果表明PAn修饰从提高材料的界面极化能力和改善粒子与硅油之间的浸润性两个方面同时增强1.7% PAn/BTO复合粒子的电流变性能。纯BTO粒子电流变性能随电场重复作用次数的增加而降低,而1.7%PAn/BTO复合粒子的电流变性能不受电场重复作用的影响。通过测试电场重复作用前后粒子的红外光谱,结果表明,在电场重复作用下,纯BTO粒子间会形成氢键作用,改变了粒子在硅油中的分散状态,因此其电流变性能稳定性较差；而1.7% PAn/BTO复合粒子在电场重复作用下不发生变化,因此能够保持稳定的电流变性能。2、在传统草酸盐共沉淀法基础上,通过在反应体系中引入丙烯酰胺“盖帽剂”制备出形貌不同的BCTO粒子。随着反应体系中丙烯酰胺浓度的增加,BCTO粒子由不规则形貌转变为纳米层状结构和由块体结构粒子组成的聚集体。在丙烯酰胺浓度为5.16g/L时,纳米层状结构BCTO由厚度为70nm的薄片状粒子通过层-层聚集而成。红外光谱和X射线衍射结果表明丙烯酰胺分子对BCTO晶体的选择性吸附是形成纳米层状结构粒子的主要原因。电流变测试结果表明,纳米层状结构BCTO粒子表现出最佳的电流变性能,其剪切应力达到65.3 kPa(E=5 kV/mm),是块状结构BCTO粒子的十多倍。介电分析表明BCTO粒子的电流变性能主要受其形貌和比表面积的影响,极性的丙烯酰胺分子对其电流变性能的增强作用不明显。3、首先通过静电作用将带正电的Ba2+离子吸附带负电的Si02纳米粒子表面,然后制备出纯度较高的TiO(C2O4)22-阴离子,通过Ba2+离子和TiO(C2O4)22-阴离子在SiO2粒子表面的反应,合成出具有核壳结构的SiO2/BTO纳米复合粒子。红外光谱、X射线衍射和扫描电镜测试表明BTO包覆在SiO2粒子表面,形成壳层平均厚度小于10nm的核壳粒子。核壳粒子电流变液的剪切应力在电场强度为4kV/mm时达到21.5kPa,为相同浓度的纯BTO粒子电流变液的4.2倍。介电测试结果表明,核壳结构是材料电流变性能和界面极化能力增强的主要原因。更多还原

【Abstract】 Electrorheological (ER) fluid is a kind of smart liquids which are composed of dielectric micro- or nano-size particles dispersed in an insulating liquid. The rheological properties of an ER suspension can rapidly and reversibly change by several orders of magnitude under an external electric field. These fantastic properties make ER fluid widely use as an electro-mechanical interface in various industrial areas. For example, shock absorbers, clutch, control valve, etc. However, the main shortcoming of conventional ER fluids which have been designed and prepared based on the dielectric polarization mechanism is low shear stress, which can not meet the requirements of industrial actual application. In 2003, Wen weijia et al first found that the ER fluid based on the urea coating barium titanyl oxalate (BTO) nano-particles could produce the giant ER effect, which overcame the historical problem of low shear stress for conventional ER fluids. They have considered that the giant ER effect was induced by the urea thin layer with coating on the surface of the BTO nanoparticles. Although the practical application of this giant ER fluid is restricted by the decomposition of urea molecules under electric field, it gives a new design thought for preparation high performance ER fluids whose ER activities have been enhanced through improving the structure of particles. Based on this research thought, the interfacial properties of BTO particles have been improved through surface modification, morphology control and core/shell structure design. At the same time, these methods are also used to avoid the negative action of the ER effects which have been induced by the decomposition of polar molecules.In this thesis, a series of ER materials, such as the BTO composites which have been modified by trace polyaniline (PAn), the chromium doped barium titanyl oxalate (BCTO) particles with nano-sandwich morphology, the silica/barium titanyl oxalate (SiO2/BTO) core/shell particles, have been prepared. The structure of these materials is characterized by X-ray diffraction (XRD), fourier transform infrared (FTIR), scanning electron micrscopy(SEM) etc, respectively. The ER and dielectric properties of the ER fluids based on these particles dispersed in methylsilicone oil have been investigated by a modified ARES 2000 rheometer and an impedance analyzer. The major experimental results are given as follows:1. PAn/BTO composites have been prepared by situ oxidation trace aniline. The measurement results of FTIR and TG-DSC show that aniline has been oxidized into polyaniline, which modifies well on the surface of BTO particles and decreases the water adsorbed on the surface of BTO particles. With the increasing of the dosage of PAn, the contact angle between the PAn/BTO composites and methylsilicone oil decreases while their wettability increases. At the same time, the ER activities for the PAn/BTO composites ER fluids first increase with increasing the dosage of PAn and then decrease. When the dosage of PAn increases up 1.7%(An/BTO=1.7 mol%), the PAn/BTO composites ER fluid shows the best ER properties and its maximal shear stress reaches 54.5 kPa (E=3.5 kV/mm), which is 3.3 times higher than that of pure BTO particles ER fluid. Compared with the pure BTO particles ER fluid, the dynamic shear stress and ER efficiency of the 1.7% PAn/BTO composites ER fluid have also been enhanced. The results of dielectric tests show that the enhancement of ER properties of 1.7% PAn/BTO composites ER fluid originates from the improving interfacial polarization of ER fluid and wettability between the particles and silicone oil, which have been attributed to the PAn modification. When the times of repeated treating on the ER fluids by the electric field increases, the ER effect of the ER fluid based on pure BTO particles decreases gradually while that of the 1.7% PAn/BTO composites keeps stable. The FTIR spectra of the particles before and after repeatedly treated by electric field are investigated, the results show that the hydrogen bond between the pure BTO particles is formed under the repeated treatment by electric field, which changes the dispersion state of BTO particles in methylsilicone oil and decreases its ER properties, so the stability of the ER properties for BTO particles is not well. There is no distinct change for the 1.7% PAn/BTO composites ER fluid before and after repeatedly treated by electric field, so it can keep stable ER properties.2. On the based of the conventional oxalate co-precipitation method, chromium doped barium titanyl oxalate (BCTO) particles with different morphologies have been prepared through adding acrylamide as a capping agent in the reaction system. With the increasing of the concentration of acrylamide, the morphology of the synthesized BCTO changes from an irregular shape via sandwich-like structure to congeries of blocks. When the concentration of acrylamide increase up 5.16 g/L, the nano-sandwich BCTO particles, which are composed of regularly aggregated nano-flakes of about 70 nm in thickness through layers by layers, have been synthesized. The structure of particles is characterized by FTIR and XRD. The results imply that the basical reason for formation of nano-sandwich particles is the selective adsorption of acrylamide on the different facets of BCTO primal particles. Compared with BCTO particles with other morphologies, the nano-sandwich BCTO particles show the best ER properties and its shear stress is up to 65.3 kPa (E= 5kV/mm), which is more 10 times higher than that of block-shaped particles. Through measuring the dielectric properties of BCTO particles ER fluids, we find that the ER properties of BCTO particles are mainly controlled by the morphologies and specific surface area of BCTO particles, and acrylamide molecules adsorbing on the surface of particles play a minor role for enhancement of the BCTO particles ER effect.3. In order to obtain SiO2/BTO core-shell composites, first Ba2+ ions are adsorbed on the surface silica nano-particles through electrostatic interaction, then TiO(C2O4)22" anions with high purity are also prepared, at last the SiO2/BTO core-shell composites are synthesized through the reaction between Ba2+ and TiO(C2O4)22- ions on the surface silica particles. The structure of particles is characterized by XRD, FTIR and SEM. The results show that the BTO coats on the surface of silica particles and form core/shell composites, whose shell is less than 10 nm in thickness. The shear stress of the SiO2/BTO composites ER fluid reach 21.5 kPa (E=4 kV/mm), which is 4.2 times higher than that of pure BTO particles ER fluid at the same condition. Dielectric analysis indicates that the structure of core/shell is the main reason to improve the ER properties and interfacial polarization of ER fluid.更多还原