Superhydrophobic and Flexible Aerogels

Abstract

Aerogels with reduced fragility and increased hydrophobicity have significant potential to expand their use as lightweight structural, insulating or shock absorbing materials especially in aeronautics, microelectronics, and sensing applications. In addition, there is a potential for extremely hydrophobic aerogels in oil-spill clean-up applications. This chapter describes synthesis, physico-chemical properties, and applications of flexible superhydrophobic silica aerogels that is to say silica aerogels with typical water contact angles >150° and high mechanical flexibility. Such materials are accessible via a two-step sol–gel process from methyl-trialkoxysilane precursors. Extreme hydrophobicity has been obtained with measured water contact angles as high as 175°. The criticality of the water droplet size on a superhydrophobic aerogel was determined to be 2.7 mm. The velocity of the water droplet on such a superhydrophobic surface has been observed to be 1.44 m/s for 55° inclination, which is close to the free fall velocity (~1.5 m/s). Elastic and rheological properties of as-prepared aerogels are also described in this chapter. Young’s modulus of the aerogels is determined by uniaxial compression test measurements. Apart from synthesis and characterization, emphasis is placed on their potential use as shock absorbing materials and efficient absorbents of oil and organic compounds in general.