Drying of Silica Gels to Obtain Aerogels:Phenomenology and Basic Techniques

Synthesis and biomedical applications of aerogels: Possibilities and challenges

“…The standard way to dry wet gels is to circumvent the capillary stresses by removing the liquid with supercritical drying approaches or following surface modifications to allow ambient pressure drying. A detail of these two methods has been addressed and elaborated by Bisson et al [182]. A brief summary of each method is included in the next subsections.…”

“…For example, one approach is ''hydrophobization'' of wet gels after gelation, which can be performed by immersing them in a hydrophobic solvent, such as alkane (hexane or heptane), and in a TMCS solution, followed by ambient pressure drying [40]. Other is the ''co-precursor'' approach, using surface modification agents, such as the MTMS precursor, which are added to the silica precursor (water glass or TMOS) to modify the surface chemistry and promote the so-called spring-back effect [182]. And, eventually, adding Drying…”

Switching silica aerogels from transparent to opaque

“…[3][4][5]. Except for an almost constant contribution due to the cuvette and absorption caused by adsorbed water (1100-2000 nm) and -OH and Si-O fundamentals (above 2200 nm) [17], the blank sample shows a significant scattering only below $500 nm (Fig.…”

“…Recently, several authors have reported the observation of an opaque phase during the adsorption or desorption of liquids such as 4 He, liquid nitrogen, or ethanol in silica aerogels [1][2][3][4][5]. Despite numerous hints and remarks, so far only a few research groups have tried to elucidate the origin of this effect by investigating the transmission or scattering of electromagnetic radiation at different stages of pore filling [1,4].…”

A Simple Process to Prepare Silica Aerogel Microparticles from Rice Husk Ash

“…This happens as a result of interfacial tension between the vapor and the liquid phases in the pores. This can be obviated by supercritical drying, that is, by drying in the absence of a vapor-liquid interface [9]. The use of surface modification agents can modify mechanical properties of wet gels in order to circumvent destruction of pore structure during drying under atmospheric or subcritical conditions [10], [11].…”