Enhancing the mechanical properties of superhydrophobic atmospheric pressure plasma deposited siloxane coatings

Abstract

Surfaces with water contact angles above 150° are regarded as superhydrophobic. In this study the use of atmospheric pressure plasma jet system called PlasmaStreamTM to deposit superhydrophobic coatings is investigated. The coatings were deposited from the following liquid precursors: HMDSO, tetramethyl cyclotetrasiloxane (Tomcats) and a mixture of Tomcats and fluorosiloxane. The objective of the study is to investigate how precursor type and deposition conditions, influences the morphology and mechanical performance of the deposited superhydrophobic coatings. Optical profilometry, AFM, SEM, Ellipsometry, XPS, Water contact angle and FTIR techniques were used to evaluate the surface roughness, morphology, thickness and chemical functionality of the deposited coatings. The mechanical properties were evaluated using the Nano Tribometer, Nano Scratch, Ultra Nanoindentation and ultrasonic abrasion tests. Superhydrophobic coatings deposited from a precursor mixture of Tomcats and fluorosiloxane yielded a substantial enhancement in coating adhesion and mechanical durability compared to the superhydrophobic coatings obtained with either Tomcats or HMDSO precursors alone. All three coatings exhibited a ‘needle-like’ morphology, however in the case of the coating deposited from the precursor mixture, a reduction in the heights of the ‘needle’ peaks (reduced roughness), combined with an increased level of cross-linking may explain the enhanced mechanical durability of this superhydrophobic coating.