Superhydrophobic aerogels

Table 4.3. Molar compositions of MTMS, MeOH, water, and ammonia used in the preparation of superhydrophobic aerogels...

Table 4.4. Contact angle (0) and velocity (v) of a water droplet on a superhydrophobic aerogel coated...

To conclude, superhydrophobic aerogels are excellent sponges for organic solvents as proven by measurements of the uptake capacity but even more, they can be almost quantitatively retrieved by a suitable thermal treatment. From a practical point of view, the solvent should be retrieved at the lowest possible temperature in order to prevent decomposition of the solvent and degradation of the aerogel itself. 

A key factor for the practical usefulness of aerogel-based hydrocarbon sorption systems is the reusability. Because aerogels are extremely expensive to produce (Chap. 26), some of the added cost must be compensated by exactly those types of practical aspects. As part of our preliminary studies on the reversibility of the sorption and desorption of superhydrophobic aerogels with various organics, the following trends were observed ... 

Pure solvents, particularly of low molecular weight (hydrocarbons, alcohols, aromatics) are absorbed and desorbed with quite good reversibility. The superhydrophobic aerogel can undergo up to 20 absorption/desorption cycles without much... 

Superhydrophobic aerogel Aerogel on which the contact angle of a water droplet with the porous external surface is >150°... 

Rao AV, Kulkami MM, Amalnerkar DP, Seth T (2003) Superhydrophobic silica aerogels based on methyltrimethoxysilane precursor. J Non-Crystal Solids 330 187 195 Reardon EJ, Poscente PJ (1984) A study of gas compositions in sawmill waste deposits an evaluation of the use of wood waste in close-out of pyrite tailings. Reclam Revegetation Res... 

D.Y. Nadargi, S.S. Latthe, H. Hirashima, and A.V. Rao, Studies on Rheological Properties of Methyltriethoxysilane (MTES) Based Flexible Superhydrophobic Silica Aerogels, Microporous Mesoporous Mater., 117, 617-626 (2009). 

Venkastewara Rao A, Hegde ND, Hrrashima H (2007) Absorptitm and desorption of organic liquids in elastic superhydrophobic silica aerogels. J Colloid Interface Sci 305 124—132... 

Roig, A, Molins, E, Rodriguez, E, Martinez, S, Moreno-Manas, M, Vallribera, A (2004) Superhydrophobic silica aerogels by fluorination at the gel stage. Chem Commun 2004(20) 2316-2317. 

Li, X M, Reinhoudt, D, Crego-Calama, M (2009) What do we need for a superhydrophobic surface A review on the recent progress in the preparation of superhydrophobic surfaces. Chem Soc Rev 36 1350 1368. Rao, A V, Kulkami, M M, Bhagat, S D (2(X)5) Transport of liquids using hydrophobic aerogels. J Colloid Interface Sci 285 413-418. 

In an altogether different approach to improve the mechanics and introduce superhydrophobic properties, in this chapter, we are presenting work on the synthesis of flexible and superhydrophobic silica aerogels derived from methyltrimethoxysilane (MTMS) and methyltriethoxysilane (MTES) precursors and their usability as efficient sorbents for oil and hydrocarbons [18, 19]. The main objective of this chapter is to provide an overview of synthesis, characterization, and most promising areas of applications. 

Figure 4.3. TEM image of a AfTMS-derived superhydrophobic silica aerogel. The scale bar length is 200 nm.

Figure 4.4. Photograph showing a water droplet placed on the surface of a superhydrophobic silica aerogel.

Measurement of runoff velocity. The runoff velocity of liquid droplets on an inclined surface coated by the superhydrophobic silica aerogel powder was quantified by recording... 

The Y value of the as-prepared aerogels was found to be 9.6 x 10 and 2.6 x 10 times smaller than those of Iron and Indium, respectively. The Y values of these aerogels are closer to those of rubber when compared with the metals mentioned above. It is only 2.6 X 10 times smaller than the Y value of rubber which is quite rarely observed in case of silica aerogels. This improvement in elastic modulus of superhydrophobic flexible aerogels with those of native silica aerogels is roughly two orders of magnitude. 

Figure 4.14. Comparison of Y value of superhydrophobic flexible aerogels with various materials.

---