Combined micro-/nanoscale surface roughness for enhanced hydrophobic stability in carbon nanotube arrays

Extreme water repellency is greatly desired for anticontamination and self-cleaning applications. Aligned multiwalled carbon nanotube arrays exhibit superhydrophobic behavior but suffer from poor hydrophobic stability and contact angle hysteresis. In this work the authors selectively grow multiwalled nanotubes onto a patterned substrate and engineer a novel high aspect ratio architecture which combines a micro- and a nano-scale roughness structure. While there is no significant difference in the static contact angle of the patterned and uniform nanotube arrays, dynamic measurements indicate a dramatic increase in hydrophobic stability for the patterned array caused by entrapped air pockets which prevent Cassie to Wenzel state transition. (c) 2007 American Institute of Physics.