Surfaces With Special Hydrophobicity Fabricated Withasimple Methodand Their Wettabilities

Superhydrophobic surfaces typically have a water contact angle higher than150°anda sliding angle less than10°. Because of their special hydrophobicity and self-cleaningproperties, superhydrophobic surfaces can be potentially applied in diverse areas such asself-cleaning coatings, mico-fluidic devices, and friction-reduction coatings. Therefore,both academic and practical research attention has been focused on superhydrophobicsurfaces.Much research effort has been devoted to generate superhydrophobic surfaces bycombining fabrication of geometric structure and modification using materials with lowfree energy. Currently there are various methods to prepare superhydrophobic surfaces,however, most of them are very complicated and the cost is relatively high. Therefore, it iscrucial to develop simple method to generate large superhydrophobic surfaces. In thisdissertation, superhydrophobic composite coatings were successfully fabricated on theinside surface of PE paper cup with a spray gun or a home-use sprayer using commercialavailable polystyrene （PS） and hydrophobic silica （H-SiO₂） nanoparticles. The influenceof weight ratio, concentration of raw materials and spray method on the surfacemorphology and wettability was analyzed. H1-SiO₂and H2-SiO₂nanoparticles arenanoparticles modified with polydimethylsiloxane and octylsiloxane, respectively. Thesuperhydrophobic composite coatings were prepared using H1-SiO₂and H2-SiO₂withthe weight ratio of H-SiO₂to PS2:1and the concentration of PS0.01g/ml both by spraygun or sprayer. PS-H1-SiO₂composite coatings exhibited better pH resistance thanPS-H2-SiO₂composite coatings. Meanwhile, both of the coatings were stable and showed self-cleaning properties, implying possible applications in anti-dirty coatings.Dynamic wetting properties of superhydrophobic surfaces are significant for theirfeasible applications. Dynamic processes of various beverages and polyacrylamide（PAM）aqueous solutions with different concentrations sliding off the superhydrophobiccomposite coatings were investigated. The results suggested that various beverage droplets,such as milk, green tea, Coca Cola, orange juice, grape juice and sprite, could roll off thesurface easily and the surfaces were completely not contaminated. The greater theviscosity of the liquid, the larger the viscous dissipation could be, so the kinetic energy ofdroplets could decrease, and the distance the droplets rolled down could be longer. For a34μl droplet impacting the superhydrophobic composite coatings from10cm height, whenthe droplet viscosity was small, the bouncing height and the bouncing frequency were low;as the liquid viscosity increased, the bounce height and the bouncing frequency increased;when the PAM concentration was higher than0.5mg/ml, along with further increment ofliquid viscosity, both of the bouncing height and the bouncing frequency decreased. For awater droplet impacting the superhydrophobic composite coatings from10cm height, thebouncing height and the bouncing frequency decreased as the droplet size increased. Theprocesses of droplets with different volumes impacting the superhydrophobic compositecoatings from various height were significantly different. For a34μl water dropletimpacting the superhydrophobic composite coatings from different height, the bouncingheight increased and the bouncing frequency decreased as the initial height of the dropletincreased. However, for a4μl water droplet impacting the superhydrophobic compositecoatings from different height, the bouncing height and the bouncing frequency increasedwhen the initial height of the droplet increased.Superhydrophobic surfaces, exhibiting a high contact angle and a low sliding angle,can be potentially applied in the transportion of micro-droplets. Moreover, the contactangle of a liquid droplet can be adjusted in a larger range when an electric voltage isapplied. In this study, the electrowettablity of various ionic liquids and KCl aqueoussolutions with different concentrations on superhydrophobic silver surfaces assembledwith thiol molecules was explored. The results showed that the electriwettability of ionicliquids were affected by the ion volume and the delocalization of charge. As the volume ofanions and cations increased, and the delocalization of charge became more intense, thesurface tension of ionic liquid decreased, and the values of contact angle, positive/negative saturated voltage and contact angle difference at saturated voltage also decreased. Theassembled molecules on the superhydrophobic surfaces also had influence on theelectrowettablity of ionic liquids. The contact angle on surfaces assembled with1H,1H,2H,2H-perfluorodecanethiol decreased more greatly than that on the surfacesassembled with n-dodecanethiol. In addition, the electrowettability of ionic liquids andKCl solution was similar when they had similar electrical conductivity. Ionic liquids had abetter application prospect than aqueous solutions due to their better performances inmany aspects.