Paper PS2-ThA9
Stable Super Hydrophobic Nanocoatings on Polymers Prepared by Gas Phase Deposition

Thursday, October 23, 2008, 4:40 pm, Room 306

The demand for super hydrophobic and oleophobic coatings in technological applications is continuing to increase particularly on inert materials such as polymers. We utilize the method of molecular vapour deposition (MVD) as a gas phase process for depositing highly uniform and conformal nanocoatings on different laser structured polymer substrates using fluorinated silanes. The challenge with such an approach is optimizing the adhesion and stability of the silane layer, particularly under conditions where moisture is present. One approach we are pursuing is to perform several alternating pre-treatments of the polymer surfaces including O₂ plasma treatment followed by gas phase reaction of the resultant hydroxyl groups with trimethylaluminum (Al₂(CH₃)₆). Subsequently the surface is exposed to water vapour. The process of alternating exposures to trimethylaluminum and water, known as atomic layer deposition (ALD), is repeated a number of times, generating an alumina (Al₂O₃) surface highly reactive towards fluorinated silanes, perfluorodecyltrichlorosilane (FDTS) – CH₃(CF₂)7(CH₂)2SiCl₃. The chemical surface modification schemes when combined with femtosecond laser structuring results in super hydrophobic/oleophobic with contact angles above 150° (with water). The stable silicon dioxide adhesion layer on the structured surfaces is prepared from silicon tetrachloride and water by a CVD process. The so formed silicon dioxide adhesion layer when subjected to sweat test is found to be stable for almost 14 days at 65°C. The conditions for creating such a stable precursor adhesion layer are dependent on the polymer substrate to be coated. The polymers tested in this study include polyoxymethylene (POM), polyethylene terephthalate (PET), polycarbonate (PC) and polyethylene (PE), and the treatment conditions varied including the effect of plasma treatment, precursor composition, and other operational parameters such as temperature, gas flow and treatment time. So, the precise chemical reactions responsible for forming such a stable super hydrophobic coatings, is best understood using angle dependent XPS, TOF-SIMS and contact angle measurements. Characterization using C₆₀ ion source on TOF-SIMS provided us the ‘softer’ depth profiling with increased ion yields. The results are discussed in terms of the molecular mechanisms of adhesion and polymers tested.