A Co-Precursor Approach Coupled with a Supercritical Modification Method for Constructing Highly Transparent and Superhydrophobic Polymethylsilsesquioxane Aerogels.

Chaoshuai Lei,Tao Xia,Chencheng Sun,Yue Zhang,Junning Li,Zijun Hu,Hailong Yang

doi:10.3390/molecules23040797

Abstract

Polymethylsilsesquioxane (PMSQ) aerogels obtained from methyltrimethoxysilane (MTMS) are well-known high-performance porous materials. Highly transparent and hydrophobic PMSQ aerogel would play an important role in transparent vacuum insulation panels. Herein, the co-precursor approach and supercritical modification method were developed to prepare the PMSQ aerogels with high transparency and superhydrophobicity. Firstly, benefiting from the introduction of tetramethoxysilane (TMOS) in the precursor, the pore structure became more uniform and the particle size was decreased. As the TMOS content increased, the light transmittance increased gradually from 54.0% to 81.2%, whereas the contact angle of water droplet decreased from 141° to 99.9°, ascribed to the increase of hydroxyl groups on the skeleton surface. Hence, the supercritical modification method utilizing hexamethyldisilazane was also introduced to enhance the hydrophobic methyl groups on the aerogel’s surface. As a result, the obtained aerogels revealed superhydrophobicity with a contact angle of 155°. Meanwhile, the developed surface modification method did not lead to any significant changes in the pore structure resulting in the superhydrophobic aerogel with a high transparency of 77.2%. The proposed co-precursor approach and supercritical modification method provide a new horizon in the fabrication of highly transparent and superhydrophobic PMSQ aerogels.

Highlights

Silica aerogels have gained extensive attention in the past decades owing to their extraordinary properties, such as their low density, nanoporous structure, high specific surface area, high optical transparency, and extremely low thermal conductivity in some chemical systems [1]
Shrinkage of the aerogels during the high temperature supercritical drying process was resulted from the rearrangement reactions in the gel network, which is ascribed to the further hydrolysis and condensation of unhydrolyzed Si–OCH3 groups
Superhydrophobic, and elastic PMSQ aerogels have been prepared via the co-precursor and supercritical modification method

Summary

Introduction

Silica aerogels have gained extensive attention in the past decades owing to their extraordinary properties, such as their low density, nanoporous structure, high specific surface area, high optical transparency, and extremely low thermal conductivity in some chemical systems [1]. Further hydrolysis and condensation of unhydrolyzed groups during the temperature supercritical drying process will lead to the pore structure coarsening with larger particle and pore size. This will result in the low transparency according to the Rayleigh scattering mode [16,17]. The particles in aerogels remain small and uniform after high temperature supercritical drying process, which is beneficial to the enhancement of the transparency of aerogels

Methods

Results

Conclusion