Superhydrophobic silica aerogels based on methyltrimethoxysilane precursor

Abstract The experimental results on the synthesis and physicochemical properties of superhydrophobic silica aerogels, with the highest ever obtained contact angle (∼173°), using methyltrimethoxysilane (MTMS) precursor, methanol (MeOH) solvent and ammonium hydroxide (NH4OH) catalyst, are reported. The molar ratios of NH4OH/MTMS (N), H2O/MTMS (H) and MeOH/MTMS (M) were varied from 4.25 × 10−2 to 3.5 × 10−1, 2 to 10 and 1.75 to 17, respectively. It has been found that the gelation time decreases with increase in N and H values and it increases with increase in M values. The bulk density of the aerogels was found to decrease with increase in N, H and M values. It has been observed that the volume shrinkage increases with decrease in N and H values and increases with M values. In the case of catalyst concentration variation, the contact angle (θ) increases slightly from 159° to 167° with increase in N values. On the other hand, in the case of H2O and MeOH variations, the θ first increases from 162° and 160° up to the values of 173° and 167° and then decreases to 160° and 159° with increase in H and M values, respectively. All the MTMS aerogels are opaque to the visible light. The aerogels retain their hydrophobicity up to a temperature of ∼480 ° C. The thermal conductivity of the aerogels was found to be around 0.095 W/m K except for the aerogels with higher bulk density (>0.3 g/cm3, at a lower H value of 2) whose thermal conductivity was around 0.109 W/m K. The aerogels have been characterized by Fourier transform infrared spectra (FTIR), thermogravimetric and differential thermal analyses (TGA-DTA) and scanning electron microscopy (SEM) techniques. The results have been discussed by taking into account the hydrolysis and condensation reactions and SEM observations.

[1]  Adrian E. Scheidegger,et al.  The physics of flow through porous media , 1957 .

[2]  T. Jesionowski,et al.  Surface properties and dispersion behaviour of precipitated silicas , 2002 .

[3]  H. Yokogawa,et al.  Hydrophobic silica aerogels , 1995 .

[4]  A. Adamson Physical chemistry of surfaces , 1960 .

[5]  D. Haranath,et al.  Effect of methyltrimethoxysilane as a synthesis component on the hydrophobicity and some physical properties of silica aerogels , 1999 .

[6]  P. Gennes Wetting: statics and dynamics , 1985 .

[7]  U. Schubert,et al.  Inorganic-Organic Hybrid Aerogels , 1994 .

[8]  P. Powell Principles of Organometallic Chemistry , 1988 .

[9]  C. J. Brinker,et al.  Hydrolysis and condensation of silicates: Effects on structure , 1988 .

[10]  A. V. Rao,et al.  Effect of methyltrimethoxysilane as a co-precursor on the optical properties of silica aerogels , 2001 .

[11]  J. Fricke,et al.  Aerogels: production, characterization, and applications , 1997 .

[12]  U. Schubert,et al.  Hydrophobic aerogels from Si(OMe)4/MeSi(OMe)3 mixtures , 1992 .

[13]  Y. Attia Sol-gel processing and applications , 1994 .

[14]  P. C. Hiemenz,et al.  Principles of colloid and surface chemistry , 1977 .

[15]  Dong‐Pyo Kim,et al.  Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel , 2000 .

[16]  R. Riedel,et al.  Synthesis of polymeric precursors for the formation of nanocrystalline Ti-C-N/amorphous Si-C-N composites , 2001 .

[17]  W. Nellis,et al.  Silica at ultrahigh temperature and expanded volume , 1984 .

[18]  C. Brinker Sol-gel science , 1990 .

[19]  Shin K. Kang,et al.  Synthesis of low-density silica gel at ambient pressure: Effect of heat treatment , 2000 .

[20]  A. V. Rao,et al.  Hydrophobic properties of TMOS/TMES-based silica aerogels , 2002 .

[21]  A. Pierre,et al.  Encapsulation of lipases in aerogels , 2001 .

[22]  K. Cholewa-Kowalska,et al.  Organic–inorganic hybrid glasses of selective optical transmission , 2001 .