The Research Of Hydrophobic And Tensile Property Of Electrospun Microfibrous Mats

Surfaces with very high water contact angles (WCAs) particularly larger than 150°are usually called superhydrophobic surfaces, which will bring great convenience to our daily life as well as in many industry processes. Conventionally, there are two approaches to produce the superhydrophobic surfaces: One is to create a rough surface on a hydrophobic surface (CA>90°), and the other is to modify the surface with materials of low surface free energy. Recently, a great deal of research has been focused on the preparation of superhydrophobic surfaces as witnessed by the large number of publications and diverse methods. Inspired by the surface super-hydrophobicity of natural plant and animal, such as lotus and silver-ragwort, artificial super-hydrophobic surfaces can generally be fabricated by a lot of approaches. However, these preparation approaches need expensive special equipment, the process is complex and the mechanical property of the superhydrophobic surfaces is poor, which affect the further application of these superhydrophobic surfaces. Therefore, it is still a challenge left to develop a simple technique providing relatively large-scale superhydrophobic surfaces with good mechanical property.In this paper, we give a brief introduction about the superhydrophobic effect. In order to solve the "bottlenecks" in the fabrication and application of superhydrophobic surfaces above, one-step production method of superhydrophobic surfaces based on the combination of theoretical analysis and experimental research was developed. We improved the traditional electrospinning via adding rotatable collector and lateral movable multi-jet unit.In this study, we want to significantly enhance the mechanical property of fibrous PS mats by adding the polyamide 6 (PA6) or polyacrylonitrile (PAN) nanofibers homogenously into PS mats via a four-jet electrospinning process, the influence of the surface structures, the number ratio of jets and the materials on the wettability of the composite electrospinning mats (PS/PA6 and PS/PAN) was studied systematically. The best parameter of composite electrospinning for produce superhydrophobic surface was discovered: PS was dissolved in a mixture of tetrahydrofuran (THF) and N, N-dimethylformamide (DMF) (3/1, wt/wt) to a fixed weight concentration of 30 wt %, a 20 wt % PA6 solution was prepared in formic acid with an ultrasonic treatment of 20 min and PAN solution was prepared at a concentration of 12 wt% with DMF. The applied voltage was 20 kV, and the tip-to-collector distance was 15 cm. The feeding rate of polymer solutions by the syringe pump was 2 mL/h. The velocity of rotatable collector and movable four-spinneret unit were 100 m/min and 7 m/min respectively. The number ratio of jets of PS/PA6 (PS/PAN) was regulated at 4/0, 3/1, 2/2, 1/3, and 0/4 to obtain the fibrous mats with various compositions of PS and PA6 (PAN). The ambient temperature and relative humidity were maintained at 25℃and 25%, respectively. The morphology, structure, composition, hydrophobicity, and mechanical property of fibrous mats are deeply investigated by tuning the number ratios of jets of PS/PA6 and PS/PAN in the fabrication process. Experiment results show that pure PS mat exhibit superhydrophobic with high WCA of 154°and low water contact angle hysteresis (WCAH) of 6°but very poor mechanical property, the pure PA6 and PAN mat was hydrophilic with a relatively excellent mechanical property. The mechanical properties of resulting mats were significantly enhanced with adding the component of PA6 (PAN) nanofibers in fibrous PS mats and regulated by tuning the number ratios of jets of PS/PA6 (PS/PAN) in the four-jet electrospinning process, the hydrophobicity of the resulting blend fibrous mats was slightly decreased with decreasing the number ratios of jets of PS/PA6 (PS/PAN), the critical number ratios of jets in composite electrospinning PS/PA6 and PS/PAN) was 2/2 and 3/1 respectively.The formation mechanism of superhydrophobicity and reinforced mechanical property was researched. The analysis of resulting fibrous mats surface morphology using field emission scanning electron microscope (FE-SEM) shows that the achievement of surface superhydrophobicity of electrospun fibrous mat was ascribed to the combination of micro and nanostructured surface roughness inherent in fibrous PS mats based on the inspiration of self-cleaning silver ragwort leaves, there is a hierarchical structure with crater and grooves on the PS fiber. It is presumed that this combination of roughness and relatively low surface free energy PS contribute to the superhydrophobicity of electrospun fibrous PS mats. Furthermore, the composite electrospun fiberous mats were in nonwowen-like structure, the network structure including a large number of entanglement and point-bonded structures among fibers became the effective points for hindering the slip of PS fibers by providing local physical or frictional entanglements, such hindrance to fiber slip can gave rise to load transfer to stiffer PA6 (PAN) fibers. The hydrophobicity and mechanical properties of fibrous mats could be regulated by tuning the number ratios of jets of PS/PA6 and PS/PAN. For example, at the critical jet ratio of 2/2 (PS/PA6), the mats showed a WCA of 150°and a three times increased tensile strength compared with that of the pure PS mats. Additionaly, the good dispersibility of PS and PA6 fibers in the blend mats was observed from the results of FE-SEM, FT-IR, and mechanical properties, indicating that the adopted four-spinneret electrospinning technique is an effective approach to fabricate the large-scale well-dispersed blend fibrous mats.