Rapid Forming of Nanowire Array on Polyvinylidene Fluoride Polymer Surfaces at Room Temperature by Ultrasonic Loading

Forming nanostructures on a substrate have been an effective approach to regulating surface properties without changing material chemical compositions. However, such nano-forming processes are generally based on thermal plastic forming that needs to heat substrate material to its melting point, which is time-consuming and induces a risk of oxidation, aging, or phase transition, especially when the material is a polymer. This research work develops a novel method to rapidly form nanowire arrays on polyvinylidene fluoride (PVDF) polymer at room temperature. Assisted by ultrasonic vibration, nanowires with a diameter of 200 nm are formed on PVDF surface within 0.7 s, while the highest forming temperature is 124 degrees C only, which is much lower than the melting point. In addition, the original beta phase of PVDF can be retained after nano-forming by adjusting ultrasonic loading time. The agglomeration mechanism of the formed nanowires on the surface was also proposed based on the transverse flow and residual stress release during ultrasonic forming process. The water contact angle measurement showed that nanowire arrays altered the surface wettability of PVDF from hydrophilic to hydrophobic. This ultrasonic-assisted processing provides a new approach for functional surface design of PVDF and rapid nanostructure forming for various applications.