Surface pinning explains the low heat transfer coefficient between water and a carbon nanotube film

The heat transfer coefficient between a single water droplet and a multiwall carbon nanotube film (buckypaper) was measured for pristine and for carboxy functionalized nanotubes by infrared thermography. The value for non-functionalized nanotubes (438 Wm−2 K−1) was more than twice as large as that for functionalized ones (204 Wm−2 K−1) even though the water to nanotube affinity is larger in the latter case as indicated by contact angle measurement. This apparent contradiction can be explained by the hydrophilic surface pinning of the droplet and the vertically periodic layered structure of the buckypaper.