| The superhydrophobicity is theoretically defined as the water contact angle on the solid surface is more than150°and the rolling angle is less than10°. In nature this phenomenon is called"Lotus Effect", a water droplet falls from the leaf with the two-length-scale hierarchical structure covered by low energy substances. Studies indicated that similar superhydrophobic surfaces could be obtained by two ways. Firstly, the surface roughness and morphology of hydrophobic material are changed. Secondly, the rough solid surface is decorated by low energy substances.The first way above was employed in this paper, in other words, both the surface roughness and morphology of high solid acrylic-based polyurethane were altered by the addition of nanosilica. However, the compatibility between organics and inorganics was not good and homogeneous dispersion of inorganics into organics was difficult because nanosilica was prone to hydrophilic and agglomerate.Based on these two issues above, nanosilica with 15±5nm in diameter was modified with silane coupling agent KH570, ethylene glycol and ethanol by ultrasonic treatment, high speed shearing and high energy ball milling, respectively. Then the modification effect was evaluated via a verity of characterization instruments such as scanning electron microscope (SEM), Mastersizer2000 particle size analyzer, Fourier- Transform Infra-Red (FT-IR) spectrometer, X-ray Diffractometer (XRD) and so on. All results suggested that a good nanosilica surface modification was acquired by high energy ball milling. Furthermore, KH570 and ethylene glycol were the real surface modifiers, while ethanol was only served as an organic medium in the course of nano- silica surface modification. So the later experiments in this paper were all done by high energy ball milling.The concentration of KH570 was also paid much more attention in this paper. And a series of modification tests with different amount of KH570 including 1wt%, 3wt%, 4wt%, 5wt%, 6wt% and 7wt% were carried out. And the results showed that the proper concentration of KH570 was between 5wt% and 6wt% for silica surface modification. Meanwhile, the effects of ball milling parameters like milling speed and milling time on the surface modification of nanosilica were investigated as well. Nanosilica was treated by high energy ball milling with different milling speeds such as 351r/min, 401r/min and 451r/min and distinct ball milling time including 3h, 3.5h and 4h. It was found that the optimal parameters were the ball milling speed equaled to 401r/min, the time was chosen as 3.5h and the concentration of KH570 was 5wt%.On the basis of distinct mol ratios between hydroxyl and isocyanate group and the water contact angle, it proper to pure high solid acrylic-based polyurethane with n(-OH)/n(-NCO) =1 was chosen to prepare nanocomposite coatings in this paper. Nano- composite coatings were obtained by combining 2.5wt%, 5wt% and 7.5wt% modified nanosilica and pure high solid acrylic-based polyurethane, respectively. And the proper- ties of nanocomposite coatings, for example, hydrophobicity, micro-indentation hardn- ess, were characterized by an optical contact angle measuring device, a nano indenter and so on. It was surprising that the superhydrophobicity of nanocomposite coating was not observed in our experiments, whereas significant alterations on other performances of nanocomposite coating caused by the addition of nanosilica occurred. Therefore, the weatherability and anti-ultraviolet of nanocomposite coating were enhanced and it was proper to be used to preserve cultural relics. And original silica powders were also used to prepare the nanocomposite coatings as the contrary specimen.
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