Tailoring Wettability Through the Surface Modification of Electro-spun Polymers by Plasma and Sol-gel Treatments

Abstract : The interaction of liquids with a materials surface is of fundamental importance to many processes including adhesion, chemical reactions, hydrodynamic transport, and surface cleanability. Surface properties can range from being hydrophilic, or oleophilic, where the liquid wets the surface and spreads, to superhydrophobic, or oleophobic, where the liquid beads on the surface and is easily displaced. The requirements for a surface to be superhydrophobic or oleophobic are low surface energies and minimal contact between the liquid and surface, which is often created by micron and nanometer scale roughness. In this work, solutions of polyurethane and polyvinylidene difluorideco-hexafluoropropylene were electrospun to create mats of micron-sized fibres. Secondary roughness was added to the polymer fibres through the use of microphase separation, incorporation of nanoparticles, sol-gel reactions and by producing beads-on-a-string morphologies. Low surface energy was added by using fluorinated polymers, or through sol-gel reactions with low surface energy alkyl siloxanes, and plasma polymerization was attempted. Water contact angles of spun fibre mats were typically in the range of 110-130o which is hydrophobic, but the water drops were often pinned to the surface by fibres penetrating the drops. Sol-gel coatings resulted in water contact angles 150o and very small tilt angles. Argon plasma treatment of the fibres resulted in water drops completely wetting the surface with very small contact angles. Better mass flow control of the monomer is required for plasma polymerization. Fibres were characterized by contact angle measurement with a digital microscope; scanning electron microscopy; FTIR and EDX spectroscopy.