硅气凝胶增强增韧的研究进展

硅气凝胶作为纳米多孔材料具有热导率低、密度小、孔隙率高等诸多优点,但强韧性差的缺点依然限制了其广泛应用。近年来,国内外学者研究制备的硅气凝胶的整体性和强韧性大为改善。从增强增韧硅气凝胶本体强度方面出发,简要介绍了其原料配比及制备工艺增强增韧的研究进展;再从材料复合硅气凝胶方面出发,综合论述了聚合物、纤维、石墨烯增强增韧的研究进展。     

新型纳米颗粒/SiO2复合气凝胶制备及吸附催化应用进展

SiO₂气凝胶作为一种新型多孔网络结构材料,具有高比表面积、低热导率及低折射率等优异性能,在多领域具有广泛的应用前景,但是纯SiO₂气凝胶存在力学强度低、质脆易裂等缺陷,严重制约了其规模化应用。因此,如何提升气凝胶的力学性能成为突破其产业化瓶颈的重点。目前,通过引入功能性增强相是改善SiO₂气凝胶多孔骨架强度和柔韧性的最有效途径之一。本综述首先介绍了SiO₂气凝胶制备及复合改性方法;然后对功能纳米颗粒/SiO₂复合气凝胶合成进行探讨,分析了不同维度纳米材料如0D金属氧化物颗粒、1D纳米管/纳米纤维、2D氧化石墨烯纳米片（GO）以及3D金属有机骨架材料（MOFs）对气凝胶孔道结构和表面物化特性的影响,最后,论述了SiO₂复合气凝胶在环境吸附催化领域中的应用潜力。     

纳米纤维素纤维凝胶特性及其应用

纳米纤维素纤维在水溶液中可以通过物理缠绕以及氢键结合的方式形成具有稳定三维网络结构的水凝胶。纳米纤维素水凝胶具有无毒性及良好的生物相容性,在生命科学领域应用前景广阔。而纳米纤维素气凝胶保持凝胶的三维网络结构,其高比表面积、低密度及优异的隔热性能等在建筑、能源电子器件、油水分离等领域也同样有着巨大的应用潜力。本文从纳米纤维素基本特性、纳米纤维素水凝胶、纳米纤维气凝胶研究及应用情况进行了介绍,并分别对纳米纤维素水凝胶与气凝胶的优异性能及应用进展进行了总结。     

新型纳米级聚酯纤维

通过采用众多纺丝技术,对纤维的结构控制已从微米级发展到纳米级。对纳米级纤维结构控制的重要性可以用两个方法来说明。一是给出模型或概念用以改善如结晶尺寸和分子取向这样的物理性质。这种方法是将宏观性能与纳米级结构联系起来,对聚合物设计和纤维结构来说是非常重要的。另一个方法是关于纳米纤维本身。此次研究将展现纳米纤维拥有哪些新的或者说优越的性能。     

高氯酸铵/石墨烯纳米复合材料的制备及热分解行为

通过溶胶-凝胶法制备了高氯酸铵/石墨烯气凝胶(AP/GA)纳米复合材料,用SEM、元素分析和XRD对其结构进行了表征,用TG-DSC-IR联用技术对其热分解行为进行了研究.结果表明,AP/GA纳米复合材料中,AP以纳米尺寸存在于石墨烯气凝胶中,AP质量分数高达94.4％,平均粒径约为69.41 nm.石墨烯对AP的热分解过程具有明显的催化作用,与AP相比,AP/GA纳米复合材料的低温分解峰消失,高温分解峰温降低了83.7℃.总分解热达2110J/g.     

常压干燥工艺制备SiO_2纳米纤维-SiO_2复合气凝胶及其表征

以正硅酸乙酯(TEOS)为硅源,原位合成的SiO_2纳米纤维为增强相,采用溶胶-凝胶法、三甲基氯硅烷(TMCS)表面改性和常压干燥工艺制备SiO_2纳米纤维-SiO_2复合气凝胶,利用SEM、XRD、FT-IR、BET和TG等手段对复合气凝胶的相关结构和性质进行表征,研究了SiO_2纳米纤维的复合对气凝胶的影响。结果表明,SiO_2纳米纤维的加入可以形成有效的骨架结构,改善气凝胶的微观形貌和空间结构,并且有着良好的兼容性、分散性和热稳定性,保持了较高的孔隙率等优良性能,所得复合气凝胶孔径为10~20 nm,孔隙率达97%。     

硅/石墨烯基自支撑薄膜的制备及电化学性能

采用简单的超声、抽滤和水合肼化学还原相结合的方法制备硅/石墨烯基自支撑薄膜,系统研究了硅含量对硅/石墨烯复合材料电化学性能的影响。结果表明：通过在石墨烯水凝胶的片层之间插入纳米硅颗粒,可以有效地控制硅体积变化,增加该复合膜的机械强度并提高其导电性。提高硅/石墨烯复合材料中硅含量的比例可以提升其可逆比容量和首次库仑效率,当硅质量分数为53%时,复合膜在0.1C倍率下的可逆比容量及首次库仑效率分别达到945.6mA·h/g和64.8%（纯硅的229倍和9倍）;继续提高硅含量的比例,可以提升其循环寿命（循环50次容量保持率60.9%、质量分数为67%的Si）,但材料比容量有所下降,说明石墨烯在稳定硅基复合材料电化学性能方面发挥着非常重要作用。     

二氧化硅气凝胶及其在保温隔热领域应用进展

二氧化硅气凝胶是目前已知最轻的固体材料，具有热导率低、孔隙率高和比表面积大等优点，被誉为新型超级保温隔热材料。然而，二氧化硅气凝胶自身存在力学性能差和制备成本高的问题，大大限制了其在保温隔热领域大规模推广应用。本文简述了二氧化硅气凝胶合成技术和力学性能增强方法，从制备过程控制、老化条件优化、热处理、纤维复合和高分子聚合物复合等方面分析了其对气凝胶性能和工艺的影响，重点介绍了近年来二氧化硅气凝胶保温隔热材料应用在航空航天、军工领域、工业管道、建筑保温以及新能源汽车等领域的研究进展，总结了其在各领域应用的技术挑战。指出未来需进一步拓展二氧化硅气凝胶的使用温区，利用共前体和化学交联等方法增强高温下的隔热性能，同时解决气凝胶纤维复材“掉粉”和微米级粉体分散不均匀等难题，尤其是新能源汽车等新兴应用领域发展迅猛，未来仍需针对新的应用需求对其合成技术进行设计和优化。     

PIPD/Cu2 纳米纤维气凝胶的制备及性能

以聚(2,5-二羟基-1,4-苯撑吡啶并二咪唑)(PIPD)为基体、三氟乙酸(TFA)和甲烷磺酸(MSA)为混酸,通过混酸剥离-去质子化诱导凝胶-冷冻干燥-惰性气氛高温处理制备出PIPD纳米纤维气凝胶.对PIPD纳米纤维气凝胶的形貌和结构进行表征,结果表明,混酸法制备PIPD纳米纤维气凝胶过程中,强质子酸破环了PIPD纤维的晶区和取向,PIPD主体的化学结构未发生明显变化.制得的PIPD纳米纤维气凝胶具有蜂窝孔结构、低密度(6.90～15.2 mg/cm3)和高孔隙率(99.1％～99.6％).当PIPD含量(以MSA和TFA总质量为基准,下同)不高于1％时,PIPD纳米纤维气凝胶无明显收缩.惰性氛围高温处理使PIPD纳米纤维气凝胶具有弹性.水平垂直燃烧、极限氧指数(LOI)、导热系数测试表明,PIPD含量为0.5％的纳米纤维气凝胶达到不可燃水平(UL-94,V-0级),LOI高达49.2％,100℃下低热传导性〔导热系数为0.052 W/(m·K)〕.此外,引入Cu2+配位交联网络提高PIPD纳米纤维气凝胶的压缩应力,增强后气凝胶的压缩应力是初始PIPD纳米纤维气凝胶的约16倍.     

氧化纤维对纳米纤维素气凝胶微球的影响

采用TEMPO/NaBr/NaClO体系氧化全漂硫酸盐针叶浆制备纳米纤维素,并以纳米纤维素为基体制备纳米纤维素气凝胶微球。研究了纤维尺寸及纤维羧基含量大小对纳米纤维素气凝胶微球的影响。结果表明:羧基含量相同时,随着超声波处理氧化纤维的时间增加,纤维尺寸越小,制备得到的纳米纤维素气凝胶微球粒径越小;羧基含量不同时,羧基含量越高,纤维越容易被解离,且在相同的超声波处理时间条件下,得到的纤维尺寸较小,气凝胶微球颗粒越小。     

硅烷偶联剂改性玻璃纤维增强硅气凝胶的研究

为了达到增强硅气凝胶力学性能的目的,采用硅烷偶联剂KH550与KH560二步改性接枝玻璃纤维,进而制备纤维增强硅气凝胶。利用扫描电子显微镜、红外光谱仪、比表面及孔径分布仪、热重-差热分析仪、导热系数仪、电子动静态疲劳试验机等对其表征。实验结果表明：硅烷偶联剂改性玻璃纤维与硅气凝胶复合后网络结构更加均匀、骨架强度更加稳定、孔径多在30 nm以下、具有良好的热稳定性;同时,改性玻璃纤维的最佳添加量为20%（质量分数）,此时其密度为0.167 g/cm³,导热系数为0.018 5 W/（m·K）,接触角为127°,抗弯强度为1.042 MPa,抗压强度为0.669 MPa,达到预期实验目的。     

Nanofibers reinforced silica aerogel composites having flexibility and ultra-low thermal conductivity

For the sake of enhancing the performance of flexible silica aerogel in practical applications, flexible SiO₂/SnO₂ nanofibers (SSNF) reinforced flexible silica aerogel composites (abbreviated as SiO₂-SSNF) were successfully prepared. Firstly, the SiO₂/SnO₂ nanofibers with fine diameter (~320 nm) and excellent flexibility were prepared by electrospinning technology. Then the aerogel composites were synthesized by adding the flexible SSNF to the silica solution and through the sol-gel method and ethanol supercritical drying technology. The effects of different content of the nanofibers on thermal conductivity and Yong's modulus of SiO₂-SSNF aerogel composites were investigated. The SiO₂/SnO₂ nanofibers were randomly dispersed in the flexible silica aerogel and the great integrity of the material result in smaller linear shrinkage, better thermal protection, and mechanical properties compared with those pure SiO₂ aerogels. The final SiO₂-SSNF aerogel composites possess excellent thermal conductivity (0.025-0.029 W/(m∙K)) and higher Yong's modulus (70 kPa), which was twice than that of the pure silica aerogel. This prepared SiO₂-SSNF aerogel composites can be better used in thermal insulation due to its excellent flexible and thermal insulation property.     

溶胶凝胶法制备SiO2气凝胶/石英纤维增强石英复合材料及其性能表征

以正硅酸乙酯、无水乙醇、去离子水为原料制备胶液后,真空浸渍石英纤维复合材料,经固化、超临界干燥成型、表面改性等工艺使其内部填充纳米级的SiO2.利用阿基米德法测试了材料的吸水率和显气孔率,利用BET法和短路波导法对气凝胶的比表面积和孔径以及材料的介电性能进行了表征,并分析了憎水机理.结果表明,填充前后复合材料的吸湿率由最初的17.36%降至1.21%,降幅高达93%,辅以防潮涂层后吸湿率更可低至为0.052%;介电常数基本没有变化,损耗角正切有所降低,降幅最高达51.2%.     

Thermal,mechanical, and acoustic properties of silica‐aerogel/UPVC composites

The properties of silica‐aerogel/UPVC composites have been investigated with emphasis on sound and heat insulation. UPVC is a material of construction for window profiles and drainage pipes. Hydrophobic silica aerogels were synthesized using silicate sodium as a precursor through a two‐step sol–gel process. The physical and textural properties of the synthesized silica aerogels such as density, surface area, and particle size were analyzed using SEM and BET analysis. Then, the synthesized aerogels were mixed with Unplastisized Polyvinyl Chloride (UPVC) compound at five different weight ratios in an internal mixer to find out the effects of silica aerogels on the thermal, mechanical, and acoustical characteristics. The prepared UPVC/aerogel composites were characterized for tensile properties, impact strength, hardness, Vicat softening temperature, thermal conductivity, sound absorption, and sound transmission loss. The results revealed that adding silica aerogel in to the matrix of UPVC increases its hardness and softening temperature while decreases impact strength. The thermal conductivity of UPVC was decreased by up to 50% using silica aerogel. The sound absorption property of UPVC was increased up to three times by using silica aerogels due to its high porosity. Silica aerogel increased the maximum sound transmission loss of UPVC in the low frequency range. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44685.     

纳米SiO2对先驱体浸渍裂解法制备SiCf/SiC复合材料力学性能的影响

以纳米SiO2为填料,采用先驱体浸渍裂解法制备2.5D-SiCf/SiC（D为维数,SiCf为SiC纤维）复合材料,研究了前驱液中纳米SiO2含量对复合材料力学性能的影响。结果表明,纳米SiO2的添加能有效抑制先驱体裂解过程中的体积收缩,提高致密度,但过量引入易导致浸渍液黏度过高,浸渍效率降低。纳米SiO2含量对材料力学性能有较大影响,添加纳米SiO2后材料的抗弯强度和断裂韧性均高于没有添加的样品,材料抗弯强度随纳米SiO2含量的增加先增大后降低。当浸渍液中纳米SiO2含量为6%时,复合材料具有优异的力学性能,抗弯强度达到211.1MPa。     

Fire retardant cellulose aerogel with improved strength and hydrophobic surface by one-pot method

Bio-based materials with multifunctional performance are getting immense attention nowadays for their environment friendly and renewable character. Inspired by toughening effect of graphene nanosheets and borate chemistry, a simple in-situ borate crosslinking in water and freeze-drying method was employed to fabricate a fire retarded bio-based aerogel. The structure of the material was evaluated and analysis by SEM, XRD, FTIR, Raman and XPS. Importantly, the bio-based aerogel has improved strength and adsorption properties due to unique structure. The compressive strength of rGO(reduced graphene oxide) + CMC (carboxymethyl cellulose) aerogel could reach 128 ± 2.1 kPa which is five times that of neat CMC aerogel. The bio-based aerogel can load more than 2500 times of self-weight. The adsorption capacity for organic solvents and oil of rGO+CMC aerogel is also greatly improved by a little rGO (1%) introducing due to its unique porous structure and hydrophobic nature of rGO. Additionally, rGO+CMC aerogel is also found fire resistant with relatively low thermal conductivity due to the borate and GO introduction.     

Graphene/Polyaniline Aerogel with Superelasticity and High Capacitance as Highly Compression-Tolerant Supercapacitor Electrode

Superelastic graphene aerogel with ultra-high compressibility shows promising potential for compression-tolerant supercapacitor electrode. However, its specific capacitance is too low to meet the practical application. Herein, we deposited polyaniline (PANI) into the superelastic graphene aerogel to improve the capacitance while maintaining the superelasticity. Graphene/PANI aerogel with optimized PANI mass content of 63 wt% shows the improved specific capacitance of 713 F g^?1 in the three-electrode system. And the graphene/PANI aerogel presents a high recoverable compressive strain of 90% due to the strong interaction between PANI and graphene. The all-solid-state supercapacitors were assembled to demonstrate the compression-tolerant ability of graphene/PANI electrodes. The gravimetric capacitance of graphene/PANI electrodes reaches 424 F g^?1 and retains 96% even at 90% compressive strain. And a volumetric capacitance of 65.5 F cm^?3 is achieved, which is much higher than that of other compressible composite electrodes. Furthermore, several compressible supercapacitors can be integrated and connected in series to enhance the overall output voltage, suggesting the potential to meet the practical application.     

Fabrication of strong and ultra-lightweight silica-based aerogel materials with tailored properties

Cross-linked silica aerogels are promising, strong, lightweight materials for photolithographic applications. The work presented here details the preparation of ultra-lightweight aerogel materials with tailored properties through the appropriate combination of silica and methacrylate polymer using laser-induced rapid photogelation fabrication technique. For fabrication, an ethanolic solution of hexanediol diacrylate, tetraorthosilicate, Eosin Y and a tertiary amine was prepared. The amounts of reactants were varied to prepare different compositions of aerogel monoliths. The solution was irradiated with a green beam from a low power laser source. The samples, after drying in supercritical ethanol, were characterized using FTIR, BET, SEM, TGA, and a mechanical testing instrument. FTIR data suggests that neither low nor high silica content has an effect on the reactivity of acrylate functionalities during polymer formation. SEM micrographs reveal that variation in silica or polymer content does not produce any phase-separated structures. Instead, uniformly distributed nano-sized polymer–silica structures were obtained for all compositions. Our results suggest that a variety of combinations of mechanical and other properties (such as densities, surface areas, pore sizes, and pore volumes) can be produced through appropriate combination for diverse applications. All these findings provide convincing evidence that the variation of silica and/or polymer content can be used to fabricate aerogels with a variety of properties, which have the depth needed for use in laser-based 3D printing technology of simple or complex structures with nearly any dimensions.     

Mechanical analysis of carbon nanofiber/epoxy resin composites

The mechanical response of epoxy resins filled without treated carbon nanofibers and carboxylated ones has been evaluated through tensile tests. The elastic properties did not improve compared to the neat epoxy resin regardless of filler content or functionalization treatment, while the tensile strength and the elongation at break were reduced for the highest filler content (1 wt%). Fractographic analysis showed that composites reinforced with carboxylated nanofibers showed better filler dispersion than those without treatment. However, in both cases, the fibers tended to agglomerate and the formation of porosity was favored. The size of bundles of nanofibers rose with the content of nanofiller and for the same addition of carbon nanofibers, the size and distribution was respectively bigger and wider for the untreated carbon nanofibers‐reinforced composites than for the carboxylated carbon nanofiber‐reinforced composites. These defects degraded the mechanical response. The dilute suspension of clusters model was applied to estimate the elastic properties, showing agreement with the experimental results. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

纤维改善SiO2气凝胶的力学和隔热性能研究进展

纤维/SiO2气凝胶复合材料因良好的力学和隔热性能具有广泛的节能应用前景,是当今国内外建筑、能源及材料等领域的研究热点.根据尺寸及形貌特征将纤维分为常规束状纤维、预制件纤维和纳米纤维三种类型,分析概述了不同类型的纤维与SiO2气凝胶复合材料的制备工艺、形貌特征以及力学和隔热性能,讨论了纤维改善SiO2气凝胶性能所存在的问题,并对以后的研究和发展趋势进行了展望.