Nanotexturing and Wettability Ageing of Polypropylene Surfaces Modified by Oxygen Capacitively Coupled Radio Frequency Plasma

Polypropylene (PP) was treated by an oxygen capacitively coupled radio frequency plasma (CCP) under a radio frequency (RF) power of 200 W for exposure time of 1, 5, and 10 min. The ageing process of the plasma-treated PP was studied at an ageing temperature of 90 °C during an ageing time up to 25 h. The formation of the nanotextures with different geometry and aspect ratio and the grafting of large number of oxygen-containing groups were achieved on as-treated PP surfaces under the oxygen CCP treatment for the increased exposure time. The hydrophilicity on the as-treated PP surfaces with the stable nanotextures was rapidly depressed during the ageing process at 90 °C due to the restructuring of chemical composition. The surface restructuring rate was dependent on the aspect ratio and the oxygen-containing groups on the nanotextured PP with increasing exposure time. The hydrophobic over-recovery to high hydrophobicity and superhydrophobicity were observed on the post-aged surfaces with the stable nanofibrils from as-treated hydrophilic surfaces. The superhydrophobicity with the low water adhesion was achieved on the post-aged surfaces preserving the nanofibrils with high aspect ratio and large distance due to the decrease of the oxygen-containing groups after the surface restructuring.