Fabrication And Properties Of Superhydrophobic Cellulosic Materials Through Nanocoating Approach

Inspired by the superhydrophbobic phenomena in nature, especially German biologist Neinhuis's research on the microscaled structures of lotus, researchers have paid great attentions to the design, fabrication and character investigation of the superhydrophobic materials. Superhydrophobic materials with remarkable self-cleaning ability have potential applications both in the fundamental researches and industrial areas.Herein, nature cellulose material was chosen as the starting material, a facile and efficient methodology is demonstrated for the fabrication of superhydrophobic cellulosic materials through the combination of surface sol-gel method and self-assembly technique. Cellulosic materials modified with azobenzene nanocoating exhibiting photo-induced reversible wettability were successfully obtained, which can be achieved between superhydrophobicity and superhydrophilicity through UV irradiation and dark storage. The main contents and conclusions are listed as follows:1. The recent researches and developments of the studies on the natural superhydrophobic phenomena were summarized. The impact factors and the fabrication techniques of superhydrophobic materials, as well as the reversible switching between superhydrophobicity and superhydrophilicity were also summarized.2. A facile and efficient methodology is demonstrated for the fabrication of superhydrophobic cellulosic materials. We have succeeded in depositing nanometer-thick titania coating onto nanofiber surface of natural cellulose substances (e.g., filter paper). Such titania nanocoating provides a unique and ideal platform for further assembly of various guest substrates onto the cellulose nanofiber surface, resulting in different functional nanoarchitectures. By taking advantage of the ultrathin titania film coating of natural cellulose substances, superhydrophobic cellulose materials were fabricated by depositing long alkyl chain silane monolayer onto the ultrathin titania film precoated cellulose fiber surface. Commercial filter paper was chosen as the raw material, and the resultant material possessed stable superhydrophobicity. The obtained superhydrophobic cellulosic materials exhibited remarkable self-cleaning ability and satisfactory long-term chemical stability, and the nanocoating deposited onto nanofibers of natural cellulosic substances without altering the initial material structures and morphologies. It is worthy to note that the physical properties of the original cellulose sheet such as flexibility and mechanical ability were also well retained after the modification of nanocoating. Water droplets were applied to collect the carbon powders sprinkled onto the surface to test the superhydrophobicity. Furthermore, we also evaluated the effct of alkyl chain length of silane and titania film thickness on the superhydrophobicity.3. Cellulosic materials modified with azobenzene nanocoating exhibiting photo-induced reversible wettability were successfully obtained, which can be carried out through low-intensity UV light irradiation and dark storage, respectively. It is based on the combination of titania nanocoating process and successive introduction of azobenzene monolayer via self-assembly technique. Subsequently the superhydrophobic cellulose sheet turns into superhydrophilic one after UV light irradiation, which can be recovered to its pristine state through being placed in the dark. The transition mechanism was also explained and discussed4. The superoleophobic cellulosic materials were introduced and fabricated. After the introduction of clay into the cellulosic sheet, the roughness of the cellulosic fibers surfaces can be enhanced, resulting in the oleophobic cellulosic materials. And the fabrication of superoleophobic cellulosic materials should be further investigated.