Dual modification of silica aerogel monoliths

A facile and versatile method based on hydrolysis and subsequent condensation of silica alkoxides through sol–gel approach is proposed to obtain an internal-hydrophobic and surface-hydrophilic silica aerogel monoliths. Wet gel monoliths were modified in turn by the hydrophobic agent trimethychlorosilane (TMCS) and hydrophilic modifier 3-aminopropylsilanetriol and finished with supercritical CO₂ drying. The silica aerogels were characterized by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), water contact angle, and microcomputer-controlled electron universal tests. The characterization on microstructure of prepared internal-hydrophobic and surface-hydrophilic silica aerogel monoliths indicated that the monoliths have a typical network structure with a porous interior, which exhibits hydrophobic performance (Max. contact angle = 137°) and a hydrophilic surface (Min. contact angle = 60°). The dually modified silica aerogel monoliths were coated with a pure acrylic emulsion layer through which the compressive strength was enhanced greatly which proved that the proposed approach is valuable to silica aerogel modification.