Hydrophobic over-recovery during aging of polyethylene modified by oxygen capacitively coupled radio frequency plasma: A new approach for stable superhydrophobic surface with high water adhesion

In this work, a new approach for the stable superhydrophobic surface with a high water adhesion has been found from an aging process at a high aging temperature of 90 degrees C during an aging time up to 24 h for the low density polyethylene (LDPE) modified by the oxygen capacitively coupled radio frequency plasma (CCP) under a radio frequency (RF) power of 200W for an exposure time of 5 min. The plasma nanotexturing produced the nanofibrils array on the LDPE surface showing the contact angle of approximately 0 degrees. During the aging process, the as-modified superhydrophilic LDPE surface underwent a hydrophobic over-recovery into the superhydrophobicity with a pinned water droplet showing the contact angle higher than 150 degrees. A time-dependent contact angle model on the nanotextured surface was developed from the Cassie's equation for the heterogeneous surface containing different wetting patches, to describe the hydrophobic over-recovery due to the surface restructuring on the nanofibrils array. The stable superhydrophobicity with the high water adhesion was attributed to the CCP modified LDPE surface with the nanofibrils composed of the heterogeneous chemical compositions of polar and nonpolar chains/groups after the aging process. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.