Ultra-low friction, superhydrophobic, plasma micro-nanotextured fluorinated ethylene propylene (FEP) surfaces

Abstract

Fluorine-containing polymers have attracted a lot of interest due to their hydrophobic nature, which enables a number of functionalities such as low friction, self-cleaning, anti-sticking, etc. Fluorinated ethylene propylene (FEP) is a copolymer of hexafluoropropylene and tetrafluoroethylene. In contrast to polytetrafluoroethylene (PTFE), FEP is melt-processable using injection molding and it is highly transparent and resistant to sunlight. Here, we transform fluorinated ethylene propylene ( FEP) surfaces to superhydrophobic using plasma processing (i.e. plasma etching with simultaneous micro-nanotexturing followed by plasma deposition). Two different plasma reactors (an inductively coupled reactor and a reactive ion etcher) and different etching conditions are used in order to micro-nanotexture FEP surfaces. Superhydrophobicity is achieved after plasma deposition of a thin (30 nm) fluorocarbon coating. Subsequently, we probe their frictional properties against water drops using a tilting stage. In particular, we demonstrate wetting control of FEP surfaces with water static water contact angle ranging from 95 o to 168 o and hysteresis down to 1–2 o . Video analysis of drops moving on different FEP surfaces shows that water drops exhibit reduced friction as etching time increases so that a hierarchical morphology is created. This is achieved using both plasma reactors, whereas the optimum performance is observed for the 10 min etched surface in a inductively coupled plasma reactor in which friction force becomes 0.7–1 μN, which corresponds to an ultra-low dynamic coefficient of friction (at least one order of magnitude lower to that of untreated FEP). • Plasma Processing for wetting control of FEP surfaces. • Superhydrophobic FEP surfaces are demonstrated. • Water drops move with reduced friction on SH FEP surfaces. • Coefficient of friction is reduced to 0.007 for SH FEP surfaces.