Reversible Superhydrophobic–Superhydrophilic Transition of ZnO Nanorod/Epoxy Composite Films

Abstract

Tuning the surface wettability is of great interest for both scientific research and practical applications. We demonstrated reversible transition between superhydrophobicity and superhydrophilicity on a ZnO nanorod/epoxy composite film. The epoxy resin serves as an adhesion and stress relief layer. The ZnO nanorods were exposed after oxygen reactive ion etching of the epoxy matrix. A subsequent chemcial treatment with fluoroalkyl and alkyl silanes resulted in a superhydrophobic surface with a water contact angle up to 158.4° and a hysteresis as low as 1.3°. Under UV irradiation, the water contact angle decreased gradually, and the surface eventually became superhydrophilic because of UV induced decomposition of alkyl silanes and hydroxyl absorption on ZnO surfaces. A reversible transition of surface wettability was realized by alternation of UV illumination and surface treatment. Such ZnO nanocomposite surface also showed improved mechanical robustness.

Influence of Heat Treatment and UV Irradiation on the Wettability of Ti35Nb10Ta Nanotubes

“…UV irradiation creates oxygen vacancies due to the formation of two coordinated bridging sites, which converts the corresponding Ti 4+ sites to Ti 3+ sites that enhance the amount of absorbed dissociated water and increase the surface free energy [35]. A gradual reversion of this hydrophilicity has been observed during dark storage [36]. The values of the roughness parameters for the polished and nanotubes Ti35Nb10Ta alloy studied herein are shown in Table 6.…”

“…The wettability of a solid surface by a liquid is determined by the liquid's surface tension, the solid surface's roughness and the solid's surface energy. The higher contact angle values found for the dark-stored nanotubes can be explained mainly by the hydrophobicity due to the Cassie-Bexter state where the liquid does not penetrate into the hollows of the nanotube surface and, consequently, faces a composite interface consisting of both solid and vapor; and also to the non-photoinduced hydrophilicity of TiO 2 [32][33][34][35][36][37]. The nanotube morphology allowed the air still trapped inside the nanotubes and the behavior to become substantially hydrophobic [32,33].…”

Nanostructured ZnO Materials: Synthesis, Properties and Applications

“…Zinc oxide nanoparticles were used as reinforcement fillers for improving the structural properties of a wide range of polymers such as rubber [159], PP [160], PET [161], epoxy resin [162,163], PMMA [164], polysulfone [165] and many others [166][167][168][169][170]. Also nanocomposites based on renewable sources were studied [171].…”

Fabrication of superhydrophobic surfaces on FRP composites: from rose petal effect to lotus effect

“…[16][17][18]20,21 Besides, the polymer matrices prepared with superhydrophobic surfaces are chiefly thermoplastics polymers, such as polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polypropylene (PP), polyethylene (PE), polystyrene (PS), polycarbonate (PC), etc. [23][24][25][26][27] Because of many excellent properties covering high specific strength, good dimensional stability, and heat resistance, ease of fabrication, relatively low cost, thermosetting polymer, and fiber reinforced plastic (FRP) composites are widely used for vessel, fluid transportation, aeronautic/space industry, and so on. 28 However, it is difficult to use a simple way to obtain superhydrophobicity on thermosetting polymers or FRP surfaces owing to the infusible and insoluble property after curing.…”

“…28 However, it is difficult to use a simple way to obtain superhydrophobicity on thermosetting polymers or FRP surfaces owing to the infusible and insoluble property after curing. 26 Therefore, it is very important to get the superhydrophobic FRP surfaces with controlled adhesion by a simple and an inexpensive method.…”