A Novel Route for Preparation of Transparent and Superhydrophobic Silica Aerogels
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A Novel Route for Preparation of Transparent and Superhydrophobic Silica Aerogels Guo-you Wu 1, Xuan Cheng 1, 2, Yu-xi Yu 1, 2, and Ying Zhang 1, 2 1 Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005, China 2 Fujian Key Laboratory of Advanced Materials, Xiamen University, Xiamen 361005, China
ABSTRACT Silica aerogels were synthesized via sol-gel processing followed by a two-step surface modification and ambient pressure drying, using methyltrimethoxysilane (MTMS) and trimethylchlorosilane (TMCS)/ethanol/n-hexane as surface modification agents. The transparent silica aerogels possessed the porosities, densities and specific surface areas in the range of 87.7–92.3%, 0.27–0.17 g·cm-3 and 852–1005 m2·g-1, respectively. The SEM and HRTEM analysis revealed the three-dimensional nanoporous structure of the silica aerogels. The presence of –CH3 functional groups on the surface of silica particles as indicated by the FTIR spectra was further confirmed by two visible exothermic peaks at 310 and 450–500 °C from the DTA curve. In addition, the silica aerogels were superhydrophobic with the contact angle as high as 160°. INTRODUCTION Silica aerogels exhibit such extraordinary properties as high specific surface area and porosity, low bulk density, thermal conductivity and dielectric constant [1], and have potential applications in thermal insulators [2], catalytic supports [3], adsorbents [4], and host materials for drug delivery systems [5]. The crucial issue in the production of silica aerogels concerns the removal of entrapped pore solvents from the wet gels while maintaining the unique texture and excellent properties of the gels. In general, the complicated process and the risks involved in the supercritical drying of the wet gels prohibit the large-scale production of silica aerogels [6]. In order to overcome these disadvantages, the surface modification procedures were used to synthesize silica aerogels by drying the gels at ambient pressure. Until recently, solvent exchange and surface modification using mixed organic solvents were simultaneously carried out by chemical reactions and a phase separation procedure to prepare hydrophobic silica aerogel pieces [7], which greatly promoted the development of ambient pressure drying technique [8-11]. However, these techniques also suffered from the prolix processing, multiple steps of solvent exchange and surface modification, which required a longer preparation time and consumed a larger amount of chemicals, affected not only the structures, but also the properties of silica aerogels. In this work, a simple and effective process was investigated to obtain transparent and superhydrophobic silica aerogels via ambient pressure drying.
EXPERIMENTAL PROCEDURES The silica aerogels were prepared using tetraethylorthosilicate (TEOS) as silica precursor. The TEOS were mixed with the co-precursor methyltrimethoxysilane (MTMS) and ethanol (EtOH) in the plastic beaker for 10 min. The deionized water and HCl catalyst we
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