An Overview on Silica Aerogels Synthesized by Siloxane Co-precursors

doi:10.15541/jim20150223

Abstract

Abstract:

Due to their unique features, such as high specific surface area, high porosity, low density, low thermal conductivity, and high transmittance, aerogels can be widely applied in the fields of thermal insulation, sound insulation and optics. However, aerogels usually tend to be destructive collapse, due to their porous structures constituted by slightly brittle skeletons, which is a negative factor to restrict their applications. According to the number and variety of non-hydrolytic groups in siloxane precursors, an overview of the literatures is presented on silica aerogels synthesized by three kinds of siloxane co-precursors, i.e. integral hydrolytic co-precursors, integral/partial and partial hydrolytic co-precursors. The characteristics of porous structures and properties in mechanics, thermal insulation, optics, and hydrophobicity are analyzed. It is an effective method by choosing appropriate precursors to realize the designs and improve mechanical behaviors of aerogels in respect of structures and properties.

Key words: silica aerogels, siloxane co-precursors, mechanical properties, Sol-Gel method, review

CLC Number:

TB303

HE Fei, YU Wan-Jun, FANG Min-Han, HE Xiao-Dong, LI Ming-Wei. An Overview on Silica Aerogels Synthesized by Siloxane Co-precursors[J]. Journal of Inorganic Materials, 2015, 30(12): 1243-1253.

Figures/Tables 9

Table 1 Organic siloxane precursors containing different non-hydrolytic groups[5]

Fig. 1 Preparation and application of superhydrophobic materials[31]

Fig. 2 Flow chart illustrating the preparation of different silica aerogels[49]

Fig. 3 Digital camera image of the flexible xerogel derived from MTMS and DMDMS co-precursor system[6]

Fig. 4 (a) Photograph and (b) stress-strain curves of a 3-point bending test on the MTMS-DMDMS gel[54]

Fig. 5 Facile synthesis of marshmallow-like gels derived from di- and tri-functional alkoxysilanes as co-precursors[54]

Fig. 6 Synthetic approach of superamphiphobic aerogels[55] (a) The synthesis for the VTMS+VMDMS marshmallow-like gel (MG1); (b) Synthetic approach for the superamphiphobic aerogels (MG2)

Fig. 7 (a) Synthesis of the precursor and (b) procedures of vacuum-drying to obtain aerogels[57]

Table 2 Comparison of performance parameters of silica aerogels prepared by different precursors

Precursors	Strength/ MPa	Elastic modulus/ MPa	Density/ (g·cm^-3)	Contact angle/(°)	Thermal conductivity/ (W·m^-1·K^-1)	Thermostability /℃
TMOS	0.031,compressed, crushed^[2]	-	0.12^[2]	Hydrophilic^[2]	0.01~0.03^[2]	600^[2]
MTMS	>9 MPa, compressed 80%, recovered^[50]	0.034~0.062 ^[1]	0.04~0.1^[1]	158~164^[1]	-	257^[1]
TMOS+PTES ^a	-	-	0.15^[5]	132^[5]	-	520^[5]
TMOS+PTES^b	-	-	0.11^[5]	121^[5]	-	520^[5]
TEOS+MTMS^a	-	-	0.107^[46]	120^[5]	-	435^[46]
TEOS+PTES^a	-	-	0.33^[5]	129^[5]	-	520^[5]
TEOS +PTES^b	-	-	0.14^[5]	115^[5]	-	520^[5]
TEOS+HMDZ ^b	-	-	0.09^[7]	146^[7]	0.08^[13]	330^[7]
MTMS+ DMDMS	~0.1, compression, recovered	-	-	hydrophobicity	-	320^[6,54]
VTMS+ VMDMS	~0.07, compressed 80%, recovered	-	0.122	150, superamphiphobic	-	170^[55]
MTMS+ GPTMS	~0.17, compressed 35%, recovered	0.46	0.104	-	0.0388	-^[56]
MPTMS+ VTMS	compression, recovered	0.117	0.085	-	0.047	-^[57]

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