Hydrophobicity recovery of corona-modified superhydrophobic surfaces produced by the electrospinning of poly(methyl methacrylate)-graft-poly(dimethylsiloxane) hybrid copolymers

Superhydrophobicity is dependent on both the surface energy and the texture of the surface. These factors are discussed in terms of a series of electrospun poly(methyl mcthacrylate)-graft-poly(dimethylsiloxane) (PMMA-g-PDMS) copolymers with different poly(dimethylsiloxane) (PDMS) content. These copolymers are synthesized via conventional free radical copolymerization of methyl methacrylate (MMA) and monomethacryloxypropyl-terminated PDMS macromonomers. It is shown how these copolymers can be electrospun to produce copolymer fibers with diameters in the 100-1000 nm range. The effect of the copolymer composition (and hence the surface energy) and the electrospinning tip-to-collector distance (TCD) on the fiber morphology is discussed. The surfaces produced by the electrospinning process show superhydrophobic properties where the preferential surface segregation of the PDMS component is combined with the roughness of the fiber surface. The surface energy of the fibers is varied by variation of the PDMS content in the copolymers as well as by post-spinning modification with corona discharge. The hydrophobicity of the surfaces shows a greater dependence on the PDMS content than on the average fiber diameter. After exposure of these fiber surfaces to corona discharge, the initial superhydrophobic surfaces become easily wettable despite the fact that much of the surface roughness is maintained after exposure. The samples show the phenomena of hydrophobocity recovery after corona exposure. The rate and extent of this recovery depends on the PDMS content and the corona exposure time. Despite the recovery, scanning electron microscopy (SEM), swelling measurements, and confocal Raman spectroscopy show that permanent surface changes have taken place. The surfaces do not recover to their original superhydrophobic state.