Poly(3-hexylthiophene) Nanotube Array Surfaces with Tunable Wetting and Contact Thermal Energy Transport

Solution casting using a sacrificial template is a simple technique to fabricate vertical arrays of polymer nanotubes. However, because of their close proximity and high aspect ratios, large capillary forces cause nanotubes to cluster as the array dries; researchers often use special drying techniques to avoid this clustering. Here, we exploit the clustering of regioregular poly(3-hexylthiophene) (rr-P3HT) nanotubes in a unique template etching process to create surfaces that exhibit tunable wetting and contact thermal energy transport. Vertical arrays of rr-P3HT nanotubes are cast from solution in nanoscale alumina templates, and a solution etching process is used to partially release the nanotubes from the template. The clustering of rr-P3HT nanotube tips upon template etching produces hierarchical surface structuring with a distinct pattern of interconnected ridges, and the spacing between the ridges increases with increased template etch times. These changes in morphology cause the water contact angle to increase from 141 degrees to 168 degrees as the etch time is increased from 4 to 12 min. When assembled into an interface, the morphological changes cause the thermal contact resistance of the vertical rr-P3HT nanotube arrays to increase linearly at a rate of approximately 6 mm(2).K/W per 2 min etch interval (after 6 min of etching is surpassed). The effective thermal conductivity of the rr-P3HT nanotube arrays is 1 +/- 0.2 W/mK independent of the etch time, which is approximately 5 times higher than the bulk rr-P3HT film value.