有机-无机复合气凝胶研究进展

气凝胶具有低密度、低热导率、高比表面积及高孔隙率等优异性能,在隔热、传感、催化、吸附、储能等领域显示出良好的应用前景。但气凝胶的多孔网络结构也造成了其强度低和韧性差等问题,严重制约了气凝胶的实际应用,有机-无机复合是一种增强气凝胶力学性能的有效方法。而且,采用有机-无机复合方法制备气凝胶还可以赋予气凝胶阻燃等其他新颖的性能。本文综述了有机-无机复合气凝胶的新研究进展,分析其原理、合成方法及相关性能,指出了有机无机复合气凝胶的优势和存在问题并展望了未来的发展方向。     

常压干燥制备二氧化硅气凝胶*

二氧化硅气凝胶是典型的纳米多孔轻质材料,由于具有独特的性能并在许多领域存在潜在的应用价值而受到广泛关注。二氧化硅气凝胶的制备传统上采用超临界干燥工艺,但此工艺成本高、工艺复杂而且具有一定的危险性。为了实现二氧化硅气凝胶的大批量生产和商品化应用,研究低成本常压干燥制备技术非常必要。目前常压干燥制备工艺已取得了较大进展,本文主要介绍了二氧化硅气凝胶的常压干燥制备方法及其特点,并概述了二氧化硅气凝胶复合材料制备的最新研究进展。以纤维和聚和物为增强体的二氧化硅气凝胶复合材料改善了气凝胶的力学性能,进一步扩宽了其应用范围。     

超低密度气凝胶的制备及应用

超低密度气凝胶是一类具有超轻质特性的多孔固体材料,较常规气凝胶具有更高的孔隙率与更为多样化的表面特性,其独特的物理与化学性质使其作为新型纳米多孔材料在诸多新兴领域得到了重要应用。在制备过程中保留超低密度气凝胶高度发达的三维孔隙结构,以及在实际应用中发挥超低密度气凝胶独特的功能特性是气凝胶领域近年来的研究重点之一。本文按照超低密度气凝胶的主要类型综述了该材料制备技术的最新研究进展,探讨了其在空间探测、阻燃隔热、储能、吸附、催化以及传感领域的应用方式;通过分析目前研究中存在的主要问题,对未来的发展方向,如突破常压干燥制备技术、开展各类复合气凝胶或结构有序可控的超低密度气凝胶的制备、系统性地研究超轻质特性对气凝胶特定功能的影响规律等进行了展望。     

常压干燥条件下乙醇对SiO_2气凝胶密度的影响

SiO_2气凝胶是一种经典的三维网状多孔纳米材料,具有低密度、高孔隙率、高比表面积、低热导率、低光学折射率和低声速等特点,在许多领域都具有巨大的应用潜力。以四乙氧基硅烷(TEOS)为硅源,采用常压干燥的方法,通过改变乙醇、氨水的物质的量之比实现对二氧化硅气凝胶的密度的研究。当TEOS、乙醇、水(0.01 mol/L草酸催化剂∶0.5 mol/L氨水催化剂)的物质的量之比分别在1∶4～10∶(1.0～3.5∶0.2～2.2)范围之间时,通过酸碱两步催化法制备得到的气凝胶密度为70～120 kg/m~3。当乙醇与氨水催化剂物质的量之比为10∶1.8时,气凝胶密度能达到76 kg/m~3,且其导热系数也能低至0.015 0 W/(m·K),降低气凝胶成本的同时所得低密度、低导热系数气凝胶也能够实现当前绿色建筑对五步节能的要求。     

TiO2-SiO2复合气凝胶：常压干燥制备及性能表征

以廉价的四氯化钛和工业水玻璃为原料,通过溶胶-凝胶法制得TiO2-SiO2复合湿凝胶,用三甲基氯硅烷(TMCS)/乙醇(EtOH)/正己烷(Hexane)混合溶液对湿凝胶进行改性,常压干燥制备了TiO2-SiO2复合气凝胶.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、红外光谱(FTIR)、X射线衍射(XRD)及N2吸附/脱附法对复合气凝胶的形貌和性质进行了分析.结果表明,TiO2-SiO2复合气凝胶具有连续多孔结构,150℃干燥后复合气凝胶的比表面积为1 076 m2·g-1,孔体积为4.96 cm3·g-1;经550 ℃热处理后,复合气凝胶仍然具有高的孔隙率,比表面积为856 m2·g-1,孔体积为3.46 cm3·g-1.吸附和光催化降解罗丹明B的结果表明,复合气凝胶同时具有较好的吸附和光催化性能,其吸附/光催化协同作用活性优于纯SiO2气凝胶和锐钛矿TiO2粉末;且重复利用四次降解率仍然可达到89%.     

高性能聚酰亚胺气凝胶的制备进展

气凝胶是轻质开孔的介孔材料,由于其特殊的性质,如低密度(0.003~0.5g/cm3)、高孔隙率(70%~99.8%)、低介电常数(~1.1)、低热导率(最低为0.012W/(m·K))和高比表面积(100~1600m2/g),因此可应用于隔热材料、隔音材料、催化剂载体、药物缓释材料、低介电材料、吸附剂等。聚酰亚胺是一类重要的高性能聚合物,近些年,聚酰亚胺气凝胶备受重视。本文综述了现有多种聚酰亚胺气凝胶的制备方法及其优缺点,并对今后的研究工作进行了展望。     

气凝胶材料的研究进展及其在航空航天领域的应用

气凝胶材料是由聚合物分子链或纳米粒子组成的一种三维纳米骨架结构的多孔材料,它具有低密度、高孔体积、高孔隙率和大比表面积等结构特点,表现出优异的光、热、声、电和力学等特性.气凝胶这种轻质材料能够很好地代替金属材料,在隔热保温、电磁屏蔽、能量储存和基体骨架等航空航天领域具有广泛的应用前景.本文介绍了气凝胶最新研究进展及其在...     

常压干燥制备酚醛树脂基炭气凝胶研究进展

以间苯二酚-甲醛为代表的酚醛树脂基炭气凝胶是一种轻质、多孔、非晶态的纳米炭材料,在催化、吸附、电化学和隔热等领域中有广阔的应用前景。但是复杂且高成本的超临界干燥工艺极大地限制了炭气凝胶的工业化制备及其应用,因此常压干燥工艺成为目前研究最为广泛的炭气凝胶制备技术之一。本文综述了酚醛树脂基炭气凝胶常压干燥制备过程的四种结构调控方法:调控溶胶-凝胶反应参数、添加模板法、纤维增强法和添加剂法,并对不同结构调控方法所制材料的结构特性及其制备过程优缺点进行了总结。最后对其发展前景进行了展望。     

新型力学性能增强二氧化硅气凝胶块体隔热材料

作为一种轻质和超高孔隙率的三维纳米多孔材料,二氧化硅气凝胶具有极低的常温导热系数,成为理想的纳米多孔超级隔热材料。然而,二氧化硅气凝胶的力学性能很差,且常压干燥制备的气凝胶整体性较差,这些都极大地限制了二氧化硅气凝胶的实际应用。近年来,通过复合或交联的方法制备得到的新型二氧化硅气凝胶,在一定程度上提高了其整体性、强度和柔韧性,使得二氧化硅气凝胶作为单独的块体材料应用成为可能。本文简要介绍二氧化硅气凝胶的多孔结构、基本性质和隔热原理,并对纤维增强、聚合物交联和其他复合二氧化硅气凝胶作为块体隔热材料的研究现状进行重点综述。最后,总结了该领域存在的关键问题,并提出未来的研究方向。     

气凝胶维度结构设计与功能化应用的研究进展

气凝胶是一类兼具重要科学研究意义和巨大工程化应用价值的纳米多孔材料, 其制备过程涉及溶胶-凝胶化学转变、结构调控、界面张力消除等基础科学问题, 在理化性能方面同时具有超低密度和超低热导率特性, 是一类理想的轻量化超级隔热保温材料, 在航空航天、交通运输等对重量要求严苛的应用领域极具吸引力. 此外, 得益于气凝胶的高比表面积、高孔隙率、连续开孔等结构特征, 其在吸附、催化、药物载体、能源和环境修复等领域也具有重要应用潜力. 因此, 近年来气凝胶及其应用获得国内外学术和产业界的极大研究兴趣. 本综述调研了自气凝胶首次报道以来相关文献与知识产权的概况, 而后以制备方法、气凝胶种类、维度结构设计、新型应用为轴, 系统概括了气凝胶的制备方法, 新型气凝胶的种类, 以维度为特色的气凝胶材料, 以及气凝胶的独特应用. 如近五年来涌现的新型超分子气凝胶、智能响应气凝胶、气凝胶纤维、气凝胶的增材制造等, 都在一定程度上颠覆了传统材料、突破了传统制备方法的局限. 最后对气凝胶近年来的发展做了简要总结和展望.     

Ambient pressure drying: a successful approach for the preparation of silica and silica based mixed oxide aerogels

Silica aerogels have received much attention in recent years as it has got a wide range of properties like high surface area, low density, high porosity, low dielectric constant, low thermal conductivity. Recently to make aerogels for commercial application ambient pressure drying has been preferred and also a cheap precursor like sodium silicate has been employed as the starting material instead of the alkoxides. In this review, attention will be given to the synthesis adopted for the preparation of silica and silica based mixed oxide/composite aerogels through ambient pressure drying. The properties of the prepared aerogels are also discussed in detail.     

Aerogels—Recent Progress in Production Techniques and Novel Applications

Aerogels are sol-gel derived nanostructured materials with extraordinary properties according to their high porosity. Though first prepared more than 60 years ago, silica aerogels became widely known only in the late 1980s when they were used in Cerenkov detectors and their potential was recognized as high performance thermal insulants. Nowadays, aerogel research has attracted many scientists from different fields, resulting in some 100 publications per year and the fifth aerogel symposium (ISA 5) in Montpellier/France in September 1997. This review will focus on recent developments in fast supercritical and ambient pressure drying processes. The state of the art with respect to structural characterization and measuring the material properties is reported including nondestructive techniques and alterations induced by invasive methods. A brief survey is given on modeling the aerogel structure and simulating properties. Special attention will be given to carbon aerogels and their organic precursors. Due to the high electrical conductivity of their graphitic backbone and the large specific inner surface areas, carbon aerogels can be considered ideal electrodes in supercapacitors and fuel cells.     

Polyurea based aerogel for a high performance thermal insulation material

Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO₂) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications and as a thermal insulation component of spacesuits.     

Polydicyclopentadiene based aerogel: a new insulation material

Lightweight polydicyclopentadiene (pDCPD) based aerogels were developed via a simple sol-gel processing and supercritical drying method. The uniform pDCPD wet gels were first prepared at room temperature and atmospheric pressure through ring opening metathesis polymerization (ROMP) incorporating homogeneous ruthenium catalyst complexes (Grubbs catalyst). Gelation kinetics were significantly affected by both catalyst content and target density (i.e., solid content), while gel solvents also played important role in determining the appearance and uniformity of wet gel and aerogel products. A supercritical carbon dioxide (CO₂) drying method was used to extract solvent from wet pDCPD gels to afford nanoporous aerogel solid. A variety of pDCPD based aerogels were synthesized by varying target density, catalyst content, and solvent and were compared with their xerogel analogs (obtained by ambient pressure solvent removal) for linear shrinkage and thermal conductivity value (1 atm air, 38 °C mean temperature). Target density played a key role in determining porosity and thermal conductivity of the resultant pDCPD aerogel. Differential scanning calorimetery (DSC) demonstrated that the materials as produced were not fully-crosslinked. The pDCPD based aerogel monoliths demonstrated high porosities, low thermal conductivity values, and inherent hydrophobicity. These aerogel materials are very promising candidates for many thermal and acoustic insulation applications including cryogenic insulation.

Effective preparation of crack-free silica aerogels via ambient drying

Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution (4–10 wt% SiO₂). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm³, and ∼675 m²/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%.     

超临界干燥法制备Fe2O3-SiO2气凝胶

以正硅酸乙酯（TEOS）和硝酸铁为原料,采用溶胶-凝胶法和超临界干燥工艺制备了Fe2O3-SiO2气凝胶,研究了Fe2O3-SiO2醇凝胶的形成条件的影响,并对所得气凝胶样品结构特性进行了初步表征．所得气凝胶样品是由直径约8nm的胶体粒子构成的低密度、高孔隙率的块状非晶固态材料．     

An Easy Way To Prepare Monolithic Inorganic Oxide Aerogels

Inorganic oxide aerogels have unique thermal, optical, electrical, magnetic, and chemical properties, which result in them potentially having a broad range of applications. However, their preparation is commonly based on a supercritical drying method, which greatly limits real applications of aerogels and their commercialization. Here we demonstrate a general method for drying wet gels to form aerogels that is based on the sublimation of organic solvent. The organic solvent must have a low surface tension, undergo sublimation easily, and have a high freezing point to allow the rapid synthesis of monolithic inorganic oxide aerogels under vacuum conditions. This cost‐effective process will facilitate application of aerogel materials. This approach may also be used for the preparation of other porous materials, whose theoretical and practical applications should be investigated.     

Elastic organic–inorganic hybrid aerogels and xerogels

Novel aerogels and xerogels with methylsilsesquioxane (MSQ, CH₃SiO_1.5) networks have been prepared by a modified sol–gel process using surfactant and urea as a phase-separation inhibitor and as an accelerator for the condensation reaction, respectively. Optimized aerogels dried under a supercritical condition not only showed the similar properties as conventional pure silica aerogels such as high transparency and porosity etc, but also demonstrated outstanding mechanical strength against compression; the aerogel drastically shrank upon loading and then recovered when unloaded, which is called a “spring-back” behavior. On ambient pressure drying, the wet gel also exhibited the similar response against compression stress originated from the capillary pressure, and thus xerogels with the comparative structure and properties to those of corresponding aerogels have also been obtained. This unusual mechanical behavior is attributed to the trifunctional flexible networks of MSQ, low silanol concentration which prevents the irreversible shrinkage, and high concentration of a hydrophobic methyl group directly attached to every silicon atom which helps re-expansion after the temporal shrinkage.     

原位法常压干燥制备疏水SiO2气凝胶及其热稳定性

在正硅酸乙酯(TEOS)酸碱两步催化的溶胶-凝胶过程中, 加入干燥控制化学添加剂(DCCA)N,N-二甲基甲酰胺(DMF)和三甲基氯硅烷(TMCS)的混合溶液, 进行原位疏水改性处理, 并结合常压干燥工艺制备了高比表面积的疏水SiO2气凝胶. 利用N2物理吸附, 全自动X射线衍射仪(XRD), 傅立叶变换红外光谱仪(FTIR), 扫描电子显微镜(SEM)等对样品的形貌结构进行了表征. 实验结果表明, 原位疏水改性比非原位疏水改性制备的SiO2气凝胶具有更大的比表面积, 可达979 m2·g-1, 气凝胶表面存在憎水性基团—CH3, 有良好的疏水性. 500 ℃热处理后, 气凝胶因失去大量的—CH3基团, 由憎水性转为亲水性; 800 ℃高温热处理后, 疏水SiO2气凝胶仍处于非晶态, 具有良好的热稳定性能.