Abstract:
A transparent film, which has a rugged surface with tiny cilia, is prepared by the tetrapod-shaped ZnO (zinc oxide) nanopowders coated with polymers including CF x  and/or CH x  functional group(s). This transparent film possesses UV-shielding and water/oil repellent functions, which can be applied to textiles, glass, woods, ceramics, tiles, plastics, and metals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 094143661 filed in Taiwan, R.O.C. on Dec. 9, 2005, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND  
       [0002]     1. Field of Invention  
         [0003]     The invention is a film, which has a rugged surface with tiny cilia, prepared by tetrapod-shaped zinc oxide nanopowders coated with a polymer including CF x  and/or CH x  functional groups. This transparent film possesses UV-shielding and water/oil repellent functions.  
         [0004]     2. Related Art  
         [0005]     Superhydrophobicity is exhibited by the unique microstructure and chemical properties of the leaves of certain plants in the nature. The characteristic of a superhydrophobic surface is that water forms spherical droplets immediately when dropping on the surface. Such a superhydrophobic surface possesses so-called “self-cleaning” function. For example, droplets formed on a lotus leaf carry the dust away by their rolling. This superhydrophobic phenomenon is caused by the roughness and low surface tension of the surface.  
         [0006]     When a liquid drops on a surface of an object, an angle is then formed between the surface and the tangent line of the drop, called contact angel θ. When the tension in the gas-solid interface (also called solid surface energy) is high, the contact angle tends to be low, which means the surface easily gets wet. Contact angle of 0 degree indicates that water spreads over and becomes a film on the surface so that the surface would completely get wet. On the contrary, if the tension in the gas-solid interface is low, the contact angle tends to be high, indicating that the surface does not easily get wet. Therefore, contact angel of 180 degrees means that the liquid forms spherical droplets and cannot wet the surface at all.  
         [0007]     When the surface with low surface energy is rougher, the contact angle would normally become higher. This is because the surface cavities with high aspect ratio may trap air so that the drop sits on a composite surface made of air and solid.  
         [0008]     Presently, there are many methods for preparing a water-repellent surface. For example, U.S. Pat. No. 5,693,236 provides a water-repellent structure and its fabrication method including the steps of: preparing a mixture by mixing a curable liquid with a needle-like material; applying the mixture onto a surface of an object; curing a liquid of the applied mixture and forming an applied layer in which the needle-like material has been mixed on a base material of the cured liquid of the mixture; forming pits and projections of the needle-like material on a surface of the applied layer by etching the applied layer under a condition where an etching rate of the base material is larger than that of the needle-like material; and coating the surface of the applied layer with a water-repellent substance. The purpose of this invention is to provide a nanocoating material that is transparent and possesses superhydrophic and UV blocking properties.  
       SUMMARY OF THE INVENTION  
       [0009]     A transparent film, which has a rugged surface with tiny cilia, is prepared by the tetrapod-shaped zinc oxide nanopowders coated with a polymer containing CF x  and/or CH x , functional groups. This transparent film possesses UV shielding and water/oil repellent functions, which can be applied to textiles, glass, woods, ceramics, tiles, plastics and metals.  
         [0010]     In the first embodiment of the present invention, the transparent film has UV shielding and water/oil repellent functions, including tetrapod-shaped zinc oxide nanopowders and a polymer containing CF x  and/or CH x  functional groups. The polymer is used to treat the surface of zinc oxide nanopowders so as to form a surface coating.  
         [0011]     On the other hand, in the second embodiment of the present invention, the transparent film has UV shielding and water/oil repellent functions, including tetrapod-shaped zinc oxide nanopowders, a transparent barrier layer, and a polymer film. The transparent barrier layer is made by coating a material such as silicon oxide (SiO 2 ) on the surface of the zinc oxide nanopowders. Furthermore, the transparent barrier layer is surface-treated by a polymer containing CF x  and/or CH x  functional groups.  
         [0012]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The present invention will become more fully understood from the detailed description given below, which is for illustration only and thus is not limitative of the present invention, wherein:  
         [0014]      FIG. 1A  is a transmission electron microscope photo showing a tetrapod-shaped zinc oxide nanoparticle;  
         [0015]      FIG. 1B  is a field emission scanning electron microscope picture showing coating made of tetrapod-shaped zinc oxide nanopowders  
         [0016]      FIG. 2  shows the first embodiment according to the invention;  
         [0017]      FIG. 3  shows the second embodiment according to the invention;  
         [0018]      FIG. 4  is an electron microscopy photo showing the ZnO—SiO 2  core-shell nanoparticle according to the invention; and  
         [0019]      FIG. 5  is a transmission electron microscopy photo showing the enlarged view of SiO 2  coating according to the invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]     A transparent film of the present invention, which has a rugged surface with tiny cilia, is made of tetrapod-shaped zinc oxide nanopowders  10  treated by a polymer containing CF x  and/or CH x  functional groups. This transparent film provides UV shielding and water/oil repellent functions.  
         [0021]     Furthermore, tetrapod-shaped zinc oxide nanopowders  10  with a HCP Wurztite structure are made by using a non-consumable electrode type of direct current plasma to vaporize solid zinc metal under the controlled pressure and atmosphere including nitrogen. Then the vaporized metal particle is oxidized through a homogeneous nucleation mechanism with a large amount of mixture of oxygen and nitrogen. The resulting ZnO nanoparticles are further quenched by a large amount of cooling air to prevent the particles from agglomeration. Details of the process have been shown in Taiwan patent No. I233321 and Taiwan patent No. I246939.  
         [0022]     A tetrapod-shaped zinc oxide nanoparticle  10  consists of four crystalline rods with hexagonal cross sections. As shown in  FIG. 1A , each zinc oxide rod  10  has a diameter between 10 nm and 100 nm, and a length between 50 nm and 1000 nm.  FIG. 1B  is a field emission scanning electron microscope picture showing coating made of tetrapod-shaped zinc oxide nanopowders.  
         [0023]     Next, a transparent film with UV shielding and water/oil repellent functions according to the invention will be described with respect to the figures.  
         [0024]      FIG. 2  shows the first embodiment of the transparent film. The transparent film includes tetrapod-shaped zinc oxide nanopowders  10  with a HCP Wurztite structure, which is capable of absorbing and shielding the UV light, and a polymer film containing CF x  and/or CH x  functional groups  20  formed on the surface of the zinc oxide nanopowder  10 . The transparent film has a rugged surface that provides UV shielding and water/oil repellent functions.  
         [0025]      FIG. 3  shows the second embodiment of the transparent film. The transparent film includes: a zinc oxide nanopowder  10 , a transparent barrier layer  15 , and a polymer film  20 . The tetrapod-shaped zinc oxide nanopowders with a HCP Wurztite structure  10  are made by using the direct current plasma technique described above. Next, to avoid the photocatalytic effect, a transparent barrier material such as silicon oxide (SiO 2 ) is coated on the zinc oxide powders  10  to form a transparent barrier layer  15  with a thickness between 1 nm and 20 nm so as to form core-shell ZnO—SiO 2  nanopowders.  
         [0026]     Then, an ionic surfactant with an amino group is used to treat the surface of the transparent barrier layer  15  that is also the surface of the ZnO—SiO 2  core-shell nanopowders for changing the state of surface charge of the ZnO—SiO 2  core-shell nanoparticles and for further improving the compatibility between the ZnO—SiO 2  core-shell nanopowders and the polymer.  
         [0027]     However, the step of surface treatment by an ionic surfactant with an amino group may not be a necessary step, depending on the properties of the polymer used.  
         [0028]     Finally, a polymer containing CF x  and/or CH x  functional groups is used to treat the surface of the transparent barrier layer  15 , which has already been treated by the ionic surfactant with an amino group, to form a polymer film  20 .  
         [0029]      FIG. 4  shows the field emission scanning electron micrograph (FESEM) of the ZnO—SiO 2  core-shell nanoparticle formed by coating a silicon oxide on the zinc oxide nanopowder  10 . The SiO 2  layer has a thickness of 5 nm.  FIG. 5  shows a transmission electron microscopy (TEM) photo of the enlarged view of SiO 2  coating according to the invention.  
         [0030]     According to the foregoing description, the present invention of the transparent film with the UV shielding and water/oil repellent functions can be achieved by using a polymer containing CF x  and/or CH x  functional groups to treat the surface of the tetrapod-shaped zinc oxide nanopowders  10 . Alternatively, the transparent film mentioned above can be achieved by using a polymer containing CF x  and/or CH x  functional groups to treat the surface of the tetrapod-shaped zinc oxide nanopowders  10  coated with the transparent barrier layer  15 .  
         [0031]     Furthermore, the above-mentioned transparent coating made of the tetrapod-shaped zinc oxide nanopowders  10  has better water/oil repellent properties, compared with those of the coating made of the rod-shaped and spherical zinc oxide nanopowders. While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments, which do not depart from the spirit and scope of the invention.