Preparation Of Functional Superhydrophobic Materials By Electrospinning

Wettability is one of the important properties of a solid surface. A directexpression of the wettability of a surface is the contact angle （CA） of a water dropleton the surface. Surfaces with a water contact angle （CA） larger than150°and awater sliding angle （SA） lower than10°are generally considered to besuperhydrophobic surfaces. The phenomenon of superhydrophobicity appearsubiquitously in nature, such as the leaf surfaces of many plants and the legs of waterstriders. These surfaces have attracted great attention in recent years due to theirspecial properties such as anti-contamination, self-cleaning and nonstick, which arewidely applied to industry applications and daily life. It was observed that thestructure of a lotus leaf consists of a combination of a two scale roughness: onearound10μm （rough structure） and one around100nm （fine structure）. And thecombination of such micro-and nano-hierarchical structures and epicuticular waxcrystalloids with low suface energy are responsible for their superhydrophobicityand self-cleaning properties. Inspired by the surface of the lotus leaf, two ideas aresummarized for the preparation of superhydrophobic surface: one is making a roughsurface from a low surface energy material, the other is modifying a rough surfacewith a material of low surface energy. Various methods and technologies have beenproposed, such as plasma etching, chemical vapor deposition, electrochemicaldeposition, sol–gel method, electrospinning and layer-by-layer assembly, etc. Thesemethods further expand the application and development of the superhydrophobicfield. Among these techniques, electrospinning has emerged as a simple andpromising method to produce surfaces with appropriate roughness and morphologydue to its ease of implementation, its lowcost, and its applicability to large-scalesuperhydrophobic surfaces. In this issue, we prepared a series of functional superhydrophobic materials using electrospinning method, and their superhydrophob-icity and some additional functions have been deeply analyzed and researched.1. Mimicking the surface structure of lotus leaf, we have preparedepoxy-siloxane modified SiO2/PVDF composite superhydrophobic material withoutcoating any of the low surface energy substance （such as fluorinated silane）. In theelectrospinning process, the epoxy-siloxane modified SiO2nanoparticles irregularlyinlayed in the substrate （PVDF） surface to generate dual-scale roughness, so that thecomposite surface exhibits excellent superhydrophobicity. The surface morphologyand superhydrophobicity can be controlled by altering the mass ratio ofepoxy-siloxane modified SiO2nanopaticles/PVDF, the contact angle is highest up to161.2±0.5°and the sliding angle is about2°. The durability of thesuperhydrophobic material was tested underwater. The result showed that theepoxy-siloxane modified SiO2nanoparticles cannot be separated from compositsurface and washed away easily when water droplet was moving thus achieving theeffect of durability and prolonging the service life.2. We have successfully prepared a multifunctional material withsuperhydrophobicity, superparamagnetism, mechanical stability and acids–basesresistance from the bead-on-string PVDF and Fe₃O₄@SiO2@POTS nanoparticles bysimple electrospinning. The Fe₃O₄@SiO2@POTS nanoparticles which haveexcellent superparamagnetism were successfully prepared and subsequentlyintroduced into PVDF precursor solution. Through electrospinning,Fe₃O₄@SiO2@POTS nanoparticles irregularly distributed in the membrane to notonly make a dual-scale roughness which is beneficial to obtain a superhydrophobicsurface but also stimulate the material turns to superparamagnetic for wider use indifferent fields. It is quite meaningful that the superhydrophobicity and self-cleaningeffect are well maintained over a wide range of pH conditions. Moreover,bead-on-string PVDF played a leading role in enhancing the tensile strength of thecomposite film which makes the superhydrophobic film hold incomparableproperties in practical application. The weight ratio of Fe₃O₄@SiO2@POTS/PVDF has great effects on the morphology and structure of the composites film, thusdisplay different superhydrophobicities and tensile strengths.3. We have successfully fabricated large-scale superhydrophobic compositefilms with enhanced tensile properties via an advanced conveyor belt electrospiningdevice. First, a multinozzle conveyor belt electrospinning device is designed to placethree （or more） nozzles on the top of the rolling conveyor belt. Large-scalefabrication without limit puts our conveyor belt electrospining device inadvantageous position. During the electrospining process, three types of fibers weremixed easily. The simultaneous presence of PS microspheres, bead-on-string PVDFfibers afford the role of increasing surface roughness so that the composite filmexhibits a superhydrophobic surface. The later introduced large diameter PAN fiberssignificantly improve the mechanical properties of electrospun sheet owing to thespecial character of PAN. The composition, superhydrophobicity and mechanicalproperties of electrospun films can be well controlled by adjusting the weight ratioof various polymers.4. Utilizing the open-close ring structure of spirobenzopyran under UV-Visiblelight irradiation, we have prepared reversible photo-responsive structured poly（SP-co-MMA） materials with tunable wettability by electrospinning. The wettabilityof the electrospun surfaces can be reversibly manipulated by the simple change ofUV-Vis light irradiation due to the photoisomerization mechanism ofspirobenzopyran chromophore. When the copolymer surface is under UV lightirradiation, the spirobenzopyran chromophore exhibits an open-ring status which ishydrophilic, whereas under visible light irradiation is hydrophobic. Electrospinningas a promising and efficient method to produce surfaces with appropriate roughnesswas used to control the morphology of the copolymer surface and significantly it isfound that the roughness of the surface can strongly influence the range of variationof the water contact angle （CA）. The results show that50%poly（SP-co-MMA）/DMF was electrospun to form all smooth fibers and the contact anglereversibly changed from146.8±0.4°to136.7±0.5°under UV-Visible light irradiation, and40%poly （SP-co-MMA）/DMF was electrospun to form allbead-on-string fibers and the contact angle reversibly changed from151.6±0.4°to132.6±0.8°.