D. B. Mahadik

Effect of concentration of trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents on surface free energy of silica aerogels

The surface free energy of a solid determines its surface and interfacial behavior in processes like wetting and adhesion which is crucial for silica aerogels in case of organic liquid absorption and transportation of chemicals at nano-scale for biotechnological applications. Here, we have demonstrated that the surface free energy of aerogels can be tuned in wide range from 5.5892 to 0.3073 mJ/m(2) by modifying their surface using TMCS and HMDZ silylating reagents. The alcogels were prepared by two step acid-base catalyzed process where the molar ratio of precursors Tetraethoxysilane (TEOS):Methanol (MeOH):Oxalic acid:NH(4)OH:NH(4)F was kept at optimal value of 1:2.7:0.18×10(-4):0.02:0.22×10(-3), respectively. To modify gel surfaces, TMCS and HMDZ concentration have been varied from 3% to 12% and such alcogels were dried at ambient pressure. It is observed from FTIR for aerogels that increase in concentration of silylating reagent resulted increase in hydrophobicity. This leads to increase in contact angle for water from 123° to 155° but leads to decrease in surface free energy from 5.5892 to 0.3073 mJ/m(2). As there is not direct method, we have used Neumanns equation of state to estimate surface energy of aerogels.

Effect of surface composition and roughness on the apparent surface free energy of silica aerogel materials

Surface chemical composition and morphology play an important role in determining the superhydrophobic behavior of solids. To provide insights on the influence of surface chemical composition and roughness on superhydrophobic behaviour of tetramethoxysilane based silica aerogel materials over a wide range, we have carried out a quantitative study of the effect of hydrophobic agent on contact angle and surface free energy of silica aerogels. The apparent surface free energy values were calculated using Zisman method and validated by Fowkes-Girifalco-Good theory.

Synthesis of transparent and hydrophobic TMOS based silica aerogels

In this paper, the preparation of tetramethoxysilane (TMOS) based silica aerogels, by sol-gel process with varying the molar ratio of silylating agent are reported. The optimal molar ratio of precursors TMOS: MeOH: NH4OH was kept constant at 5:14.2:0.93 × 10-4, respectively, and concentration of silylating agent, hexamethyldisiloxane (HMDSO) were varied from 2% to 12% of the solvent. The retrieved aerogels have been characterized by apparent density, % porosity, Thermal conductivity, Fourier Transform Infrared Spectroscopy (FTIR), Thermo-gravimetric and Differential Scanning Calorimetry (TGA-DSC) and contact angle measurements. The effect of humidity on silica aerogels has been studied. The thermal analysis indicates thermal stability of hydrophobicity retains up to 329 °C.

Methyltrimethoxysilane based flexible silica aerogels for oil absorption applications

The experimental results on the synthesis of flexible and superhydrophobic silica aerogels using methyltrimethoxysilane (MTMS) precursor by a two-step (acid-base) sol-gel process followed by the supercritical drying are reported. The effects of various sol-gel parameters on the flexibility of the aerogels have been investigated. The aerogels of different densities were obtained by varying the molar ratio of MeOH/MTMS(S) from 14 to 35, with lower densities for larger S values. It has been observed that the Youngs modulus (Y) decreased from 14.11 × 104 to 3.43×104 N/m2 with the decrease in the density of the aerogels from 100 to 40 kg/m3. Simultaneously, the aerogels are superhydrophobic with a contact angle as high as 169°. The superhydrophobic aerogels are thermally stable up to a temperature of 463 K, above which they become hydrophilic. The aerogels have been characterized by bulk density, percentage volume shrinkage, and porosity measurements. The microstructures of the aerogels have been studied usin...

Surfactant doped silica aerogels dried at supercritical pressure

By combining the molecular silica precursor methyltrimethoxysilane (MTMS) with methanol, water and Tween-80 solution, we get surfactant-doped silica alcogels. The wet alcogels can be exchanged with methanol and then supercritically extracted with nitrogen to produce surfactant-doped silica aerogels (SDSAs). SDSAs represent a new class of aerogels that are composed of aggregated submicron porous particles that have tunable interparticle nanoporosity. As we increased the percentage of surfactant, the physical properties of silica aerogels changes. In this study we characterized the SDSAs by SEM for morphological study, FTIR for the material composition, contact angle for hydrophobicity determination and thermal conductivity measurements are carried out for thermal insulation application.