Titanium Oxide Sol–Gel Induced Wrinkling of Electrospun Nanofibers

TiO₂ sol–gel reaction induces nanowrinkling along the surface of electrospun poly(vinyl alcohol) (PVA) nanofibers. Nanowrinkling along nanofibers is influenced by electrospinning voltage, degree of nanofiber crosslinking, and the repetitive immersion of nanofibers in TiO₂ precursors. Crosslinked nanofibers are dipped in alternating solutions of titanium tetraisopropoxide (TTIP) and water for up to five cycles. Interestingly, nanowrinkles only form along nanofibers that are spun at 45 kV and treated with three or more cycles of sol–gel precursor. Spectroscopy reveals that more PVA hydroxyl groups populate the nanofiber surface when electrospinning occurs at 45 kV than at 15 kV. In turn, surface PVA hydroxyl groups appear to nucleate TiO₂ growth. Scanning probe phase micrographs confirm modulus differences between the attached TiO₂ particles and PVA's surface. Those moduli differences result in wrinkling, as TTIP-treated nanofibers undergo repetitive cycles of water swelling and isopropanol deswelling.