Hydrophobic Modification on the Surface of SiO₂ Nanoparticle: Wettability Control

Good control of the morphology, particle size, and wettability of silica nanoparticles is of increasing importance to their use in a variety of fields. Here, we propose a strategy to tune the surface wettability of nanosilica by changing the dosage of a chemical modifier. A series of measurements, including scanning electron microscopy (SEM), laser scatting technique, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry, and surface hydroxyl number and water contact angle measurement, were conducted to verify the surface chemistry and wettability of these nanoparticles. Through controlled chemical modification, the contact angle of the treated nanoparticles increases from 34.7 to 155° with increasing amount of dichlorodimethylsilane (DCDMS) within a molar ratio (MR) between DCDMS and nanoparticles of 5.17. The number of hydroxyl groups covered on the particle surface decreases gradually from 1.79 to 0.47, and the surface grafting rate could reach 73.7%. As the addition of dichlorodimethylsilane equals MR 5.17, the contact angle reaches the maximum value of 155°, which displays excellent superhydrophobicity. After surpassing the point of MR 5.17, the contact angle does not increase but starts to decrease, ultimately remaining stable at 135°. It can be concluded that the surface wettability of nano-SiO₂ particles can be precisely modulated by varying the amounts of the modifier. Furthermore, the modulating mechanism of the process occurring on the surface of SiO₂ particles has been investigated at the molecular level.