Self-cleaning property is very useful in applications such as building walls or other structural surfaces to reduce its washing cycle or recoating frequency. Other potential application includes textiles and fabrics. Two of the most commonly used concepts for self-cleaning surfaces are superhydrophobicity and photocatalysis and both concepts have been tested using electrospun fibers.
The concept of superhydrophobicity for self-cleaning comes from the assumption that rolling water droplets down the superhydrophobic surface will pick dirt on it and gets washed away For a surface to be considered superhydrophobic, it should have a static angle more than 150°, and a contact angle hysteresis (CAH) of less than 10°. A low CAH is necessary for the water droplets to roll off the surface with a slight tilt.
Several researches have been able to produce electrospun surfaces with superhydrophobicity. Such property comes about from a combination of surface texture and material used. An interesting result of electrospun fibrous surface is that a material that does not exhibit superhydrophobicity as smooth membrane can be made superhydrophobic when electrospun into fibers.Al-Qadh et al (2015) was able to prepare superhydrophobic and self-cleaning polysulfone non-wovens by electrospinning. In agreement with other studies, contact angle of more than 150° can be obtained for beads or beaded fibrous surface. As the morphology transit into fibrous form, the surface contact angle reduces to about 130°. Although beads and beaded fibers showed greater surface contact angle, their mechanical strength is much lower than smooth fibers. There are other methods of increasing surface contact angle of electrospun fibers. Through the selection of materials, solvent used and control of electrospinning environment, fibers with surface pits and pores may be produced. These surface textured fibers generally exhibit higher surface contact angle compared to smooth surface fibers. Using THF/DMF weight ratios of 2/2 and 1/3 and polystyrene (PS) solution concentration of 30 wt%, fiber with numerous and evenly distributed pits and grooves were electrospun. Subsequently, water contact angle of 158° and 1607deg; respectively were obtained. For the nonwoven membrane with the higher water contact angle, the roll-off angle was 8° thus satisfying the criteria of superhydrophobicity [Miyauchi et al 2006].
The other concept for self-cleaning involves using photocatalytic materials. Self-cleaning is achieved from the degradation of stains. Inorganic materials such as TiO2 are commonly used for such application due to their photocatalytic properties. Bedford and Steckl (2010) conducted a study comparing the different methods of incorporating TiO2 into electrospun cellulose acetate (CA) fibers. Methods of incorporation were surface coating of fibers by dipping, core (CA) sheath (TiO2/CA blend) fibers and core (CA) sheath (TiO2 only) fibers. Self-cleaning properties were tested by the degradation of blue dye stain. Their result showed that only electrospun core (CA) sheath (TiO2 only) fibers fully degrades the blue dye in 24 hours. For surface coated TiO2 on CA fibers, degradation of the stain was only to 20% of initial concentration. For core-sheath fibers with TiO2/CA blend sheath, degradation rate was significantly slower than TiO2 only sheath, core-sheath fibers. This is probably due to a layer of CA coating the TiO2 particles and reducing its photocatalytic effectiveness on the stain.
Published date: 21 March 2017
Last updated: -
▼ Reference
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Al-Qadhi M, Merah N, Matin A, Abu-Dheir, Khaled M, Youcef-Toumi K. Preparation of superhydrophobic and self-cleaning polysulfone non-wovens by electrospinning: influence of process parameters on morphology and hydrophobicity. J Polym Res 2015; 22: 207.
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Bedford N M and Steckl A J. Photocatalytic Self Cleaning Textile Fibers by Coaxial Electrospinning. Applied Materials and Interfaces 2010; 2: 2448.
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Miyauchi Y, Ding B, Shiratori S. Fabrication of a silver-ragwort-leaf-like super-hydrophobic micro/nanoporous fibrous mat surface by electrospinning. Nanotechnology 2006; 17: 5151.
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