Spectral and Texture Properties of Hydrophobic Aerogel Powders Obtained from Room Temperature Drying.

Dimitar Shandurkov,Stoyan Gutzov,Ivanka Spassova,Petar Ignatov

doi:10.3390/molecules26061796

Abstract

Attenuated Total Reflectance Infrared (ATR-IR) spectroscopy and texture measurements based on nitrogen adsorption-desorption isotherms are combined to characterize silica aerogel granules with different degrees of hydrophobicity. The aerogels were prepared from tetraethoxysilane via a room temperature hydrolysis-gelation process, solvent exchange, hydrophobization, and drying at subcritical conditions. The dependencies between the texture properties, pore architectures, surface fractal dimensions, and degree of hydrophobicity of the samples are extracted from the ATR-IR spectra and the adsorption-desorption isotherms. The IR absorption in the region of the Si-O-Si and Si-OH vibrations is used for a description of the structural and chemical changes in aerogel powders connected with their surface hydrophobization. The Frenkel–Halsey–Hill (FHH) theory is applied to determine the surface fractal dimension of the powder species.

Highlights

IntroductionA special class of sol-gel materials is aerogels, which are known for their extremely low densities (ranging from 0.001 to 0.5 g/cm3 ), low optical refraction index (1.002), low thermal conductivity (0.02 W/m·K), speed of sound through a material (70 m/s), and a relative dielectric constant 1.008 at 3–40 GHz [3]
It is evident that hydrophobization leads to a decrease in the bulk density of the aerogel materials here
A new approach to describe the hydrophobization of sol-gel silica with trimethyl chlorosilane (TMCS), based on the relative intensities of the Attenuated Total Reflectance Infrared (ATR-IR) peaks, is proposed

Summary

Introduction

A special class of sol-gel materials is aerogels, which are known for their extremely low densities (ranging from 0.001 to 0.5 g/cm3 ), low optical refraction index (1.002), low thermal conductivity (0.02 W/m·K), speed of sound through a material (70 m/s), and a relative dielectric constant 1.008 at 3–40 GHz [3]. The possibilities for the incorporation of optically active hybrid molecules in hydrophobic aerogel granules were discussed [7]. A useful approach for the impregnation of hydrophobic aerogel granules with [Tb(phen)2 ](NO3 ) complexes was described using high-porosity aerogel granules and powders, at about 95%. Colloidal techniques for the preparation of impregnated porous silica for optical purposes were discussed in [8]

Methods

Results

Conclusion