Creating Superhydrophobic Polycarbonate Fiber Network from Hydrophilic Polycarbonate through Electrospinning
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Creating Superhydrophobic Polycarbonate Fiber Network from Hydrophilic Polycarbonate through Electrospinning Shuangwu Li1 and Asa H. Barber2 1 Department of Materials, Queen Mary College, University of London, Mile End Road, London, E1 4NS, United Kingdom. 2 Department of Materials, Queen Mary College, University of London, Mile End Road, London, E1 4NS, United Kingdom. ABSTRACT Considerable research has focused on the formation of superhydrophobic surfaces utilizing both the chemical composition of surfaces and geometric effects. In this study, a superhydrophobic polycarbonate (PC) network surface was produced from hydrophilic polycarbonate through electrospinning process. Complex surface geometries often related to material roughness is used to evaluate the wetting behavior of electrospun polycarbonate fiber network. The surface properties of electrospun polycarbonate fibers are therefore examined with the potential to exploit the fibers through enhancing hydrophobic behavior. Characterization and analysis of PC electrospun fiber and PC film surfaces were carried out to compare surface roughness with wetting contact angle. Analytical models are used to describe hydrophobicity in terms of roughness. INTRODUCTION A number of works have examined surface geometry in order to explain the resultant wetting behavior with water droplet. To achieve a superhydrophobic surface, Lau et al. have demonstrated the creation of a superhydrophobic surface in a vertically aligned carbon nanotube forest with a hydrophobic polytetrafluoroethylene (PTFE) coating on the nanotube’s surface [1]. The PTFE increased the hydrophobicity of the carbon nanotubes, illustrated through the relatively low PTFE surface energy of 18 mJm-2, in addition to the large aspect ratio of the nanotube fiber arrays that approximated to an extremely rough surface [1].The same principle was demonstrated by Huang et al using a superhydrophobic surface of aligned carbon nanotubes coated with a thin layer of zinc oxide (ZnO) film [2]. Nanofiber networks of other materials as opposed to carbon nanotubes have also been used to create superhydrophobic surfaces. Han et al have demonstrated a coaxial electrospinning process with poly ( -caprolactone) (PCL) as a core material and a low surface free energy Teflon AF fluoropolymer as a shell material [3]. The PCL provided a structural fiber whereas the Teflon shell, effectively a coating for the PCL, providing the surface layer. Water droplets on these electrospun fiber surfaces effectively formed large contact angles due to the presence of the Teflon. However Feng et al [4] have shown that the production of a nanofiber mesh of PVA using a template extrusion process gives a water contact angle of 171.2 ± 1.6°, when compared to a water contact angle of 72.1 ± 1.1° on a smooth PVA film surface. Feng et al considered that an increase in the surface roughness of a polymer can increase the contact angle using arguments related to Wenzel’s equation [5]. However, Wenzel’s equation indicates that a hydrophobic surface becomes more
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