Transparent, Highly Insulating Polyethyl- and Polyvinylsilsesquioxane Aerogels: Mechanical Improvements by Vulcanization for Ambient Pressure Drying
Transparent, Highly Insulating Polyethyl- and Polyvinylsilsesquioxane Aerogels: Mechanical Improvements by Vulcanization for Ambient Pressure Drying
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DOI：
10.1021/acs.chemmater.6b01936
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发表时间：
2016-10-11
影响因子：
8.6
通讯作者：
Nakanishi, Kazuki
中科院分区：
文献类型：
--
作者：
Shimizu, Taiyo;Kanamori, Kazuyoshi;Nakanishi, Kazuki
二氧化硅气凝胶是一种独特的多孔材料，具有高的可见光透明度和低的热导率。但由于二氧化硅本身的脆性限制了其在实际应用中的广泛性，目前的研究主要集中在通过有机无机杂化等方法来改善材料的力学性能。本文首次报道了聚乙烯倍半硅氧烷（PESQ CH3CH2SiO1.5）和聚乙烯倍半硅氧烷（PVSQ CH 2 =CHSiO1.5）气凝胶的合成。通过在基于表面活性剂的溶液中的两步酸-碱溶胶-凝胶反应获得的所得PESQ和PVSQ气凝胶表现出可见光透射率和抗压缩的柔性而不塌陷。正电子湮没寿命谱（帕尔斯），这些气凝胶的微观结构的变化进行了系统的研究，以澄清来自取代基的性质的差异。此外，使用自由基引发剂在PVSQ湿凝胶上的后固化诱导固体网络中的乙烯基的聚合，从而产生具有更高压缩模量和回弹性的机械增强的气凝胶。这种化学改性类似于硅橡胶材料中的硫化，有助于通过环境压力干燥生产具有与气凝胶相当的性能的干凝胶。由于从PVSQ的硫化获得的所得干凝胶显示出15.3 m（-1）K-1的足够低的热导率，这些新型聚倍半硅氧烷材料有希望用于透明气凝胶/干凝胶超级绝缘体。
Silica aerogels are unique porous materials possessing high visible-light transparency and low thermal conductivity. However, the practical applications are limited due to the native fragility of silica, and a lot of research focuses on the improvement of mechanical properties by organic inorganic hybridization, and so forth. Here, the first synthesis of polyethylsilsesquioxane (PESQ CH3CH2SiO1.5) and polyvinylsilsesquioxane (PVSQ CH2=CHSiO1.5) aerogels is reported. The resultant PESQand PVSQ aerogels obtained through a two-step acid-base sol-gel reaction in a surfactant-based solution exhibit visible-light transmittance and flexibility against compression without collapsing. The microstructural variations of these aerogels are systematically investigated by positron annihilation lifetime spectroscopy (PALS) in order to clarify the differences in properties derived from substituent groups. Furthermore, a post cure on the PVSQ wet gel using a radical initiator induces polymerization of vinyl groups in the solid network, resulting in mechanically reinforced aerogels with higher compressive modulus and resilience. This chemical modification, similar to vulcanization in silicone rubber materials, helps to produce xerogels with comparable properties to those of aerogels via ambient pressure drying. Since the resultant xerogel obtained from the vulcanization of PVSQ shows sufficiently low thermal conductivity of 15.3 m(-1) K-1, these novel polysilsesquioxane materials are promising for transparent aerogels/xerogels superinsulators.