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Microstructural and physical properties of the ambient pressure dried hydrophobic silica aerogels with various solvent mixtures

机译:具有各种溶剂混合物的常压干燥疏水性二氧化硅气凝胶的微结构和物理性质

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摘要

The experimental results on the microstructural and physical properties of the ambient pressure dried hydrophobic silica aerogels with various solvent mixtures have been reported. The aerogels were prepared with sodium silicate precursor, ammonium hydroxide catalyst, trimethylchlorosilane (TMCS) silylating agent, solvent mixture of methanol-isopropanol (MeOH/IPA) and various aprotic solvent mixtures namely, hexane and benzene (HB), hexane and toluene (HT), hexane and xylene (HX), heptane and benzene (HpB), heptane and toluene (HpT), heptane and xylene (HpX). The physical properties of the aerogels such as % of volume shrinkage, density, % of optical transmission, surface area, % of porosity, pore volume, thermal conductivity and heat capacities of the aerogels were studied. The hydrophobicity of the aerogels was studied by contact angle measurements. The HX and HpX aerogels have been found to be more hydrophobic (contact angle, theta 155 degrees) than the other aerogels. It has been observed that the % of weight increase is highest (1%) for the HT aerogels and lowest (0.25%) for HpX aerogels by keeping them at 70% humidity for 350 h. Further, the aerogels have been characterized by pore size distribution (PSD), Fourier transform infra red spectroscopy (FTIR) and thermogravimetric and differential thermal (TG-DGA) analysis and transmission electron microscopy (TEM) techniques. The results have been discussed by taking into account the surface tension, vapor pressure, molecular weight and chain length of the solvents, Low density (0.051 g/cc), hydrophobic (165 degrees), transparent (85%), low thermal conductive (0.059 W/m K), low heat capacity (180 kJ/m(3) K) and highly porous (97.38%) silica aerogels were obtained with HpX solvent mixture. (c) 2007 Elsevier B.V. All rights reserved.
机译:已经报道了具有各种溶剂混合物的常压干燥的疏水性二氧化硅气凝胶的微观结构和物理性能的实验结果。气凝胶由硅酸钠前体,氢氧化铵催化剂,三甲基氯硅烷(TMCS)甲硅烷基化剂,甲醇-异丙醇(MeOH / IPA)的溶剂混合物和各种非质子溶剂混合物即己烷和苯(HB),己烷和甲苯(HT)制备),己烷和二甲苯(HX),庚烷和苯(HpB),庚烷和甲苯(HpT),庚烷和二甲苯(HpX)。研究了气凝胶的物理性质,例如体积收缩率,密度,光透射率,表面积,孔隙率,孔体积,导热率和热容量百分比。通过接触角测量研究了气凝胶的疏水性。已发现HX和HpX气凝胶比其他气凝胶更疏水(接触角,θ 155度)。已经观察到,HT气凝胶的重量增加百分比最高(1%),HpX气凝胶的重量增加最低(0.25%),方法是将其在70%的湿度下保持350小时。此外,气凝胶的特征在于孔径分布(PSD),傅立叶变换红外光谱(FTIR)以及热重和差热(TG-DGA)分析以及透射电子显微镜(TEM)技术。通过考虑表面张力,蒸气压,溶剂的分子量和链长,低密度(0.051 g / cc),疏水性(165度),透明(85%),低导热性(使用HpX溶剂混合物获得0.059 W / m K),低热容(180 kJ / m(3)K)和高度多孔(97.38%)的二氧化硅气凝胶。 (c)2007 Elsevier B.V.保留所有权利。

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