Facile stearic acid modifications of alumina nanoparticles for superhydrophobic coating

In this study, alumina nanoparticles were modified with stearic acid (SA) dissolved in ethanol solution via facile techniques, which were soaking and refluxing. The effects of these modification techniques on the thermal behaviors and the functional groups of the SA-modified alumina were investigated. Stearic acid was successfully modified onto alumina nanoparticles using both techniques. In comparison, the refluxing technique yielded a higher degree of SA modification, corresponding to a grafting density of 2.59 molecules·nm‒2, which is approximately twice that of the soaking technique. Then, the SA-modified alumina via refluxing technique was mixed with polydimethylsiloxane (PDMS) and spray coated on glass slides. The effects of coating layers and the SA-modified alumina content on the wettability and optical property were studies. The 4-layered coating containing 10 wt% of SA-modified alumina exhibited superhydrophobic property with a water contact angle of 150.0° and the contact angle hysteresis of 6.2°. It also showed excellent self-cleaning performance. However, transmittance of 4-layered coating reduced dramatically. The results showed that increasing the number of coating layers enhanced surface wettability but adversely affected optical transmittance due to increased light scattering. Therefore, a balance between wettability and optical transparency must be considered. These findings indicated that SA-modification effectively enhanced the hydrophobicity of alumina particles, and the incorporation of these SA-modified particles introduced sufficient roughness to further improve hydrophobicity. The progress in the surface modification and the utilization of a spray coating method highlight the potential for scalable and facile fabrication of superhydrophobic coating.