Hot embossing of PTFE: Towards superhydrophobic surfaces

• Published in: Applied surface science 2011, Vol.257 (6), p.2353-2360
• Main Authors: Jucius, D., Grigaliūnas, V., Mikolajūnas, M., Guobienė, A., Kopustinskas, V., Gudonytė, A., Narmontas, P.
• Format: Article
• Language: English
• Subjects: Arrays; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Contact; Contact angle; Cross-disciplinary physics: materials science; rheology; Embossing; Exact sciences and technology; Flattening; Glass transition temperature; Hot embossing; Hydrophobicity; Materials science; Physics; Pits; Polytetrafluoroethylene; Polytetrafluoroethylenes; Softening; Solid-fluid interfaces; Surface treatments; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Two dimensional; Wetting
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2010.09.102

▶ PTFE was hot embossed above the glass transition temperature. ▶ Impact of temperature, pressure and time on pattern transfer was tested. ▶ Water repelency was improved up to the superhydrophobic region. Three types of reusable stamps with features in the form of 2D arrays of pits having lateral dimensions in the range of 2–80 μm and heights of 1.5–15 μm were successfully employed for the hot embossing of PTFE at temperatures up to 50 °C above the glass transition temperature of PTFE amorphous phase. Due to the softening of PTFE at the temperatures used in this study, we were able to decrease imprint pressure significantly when comparing with the imprint conditions reported by other authors. Impact of the imprint temperature, pressure and time on the fidelity of pattern transfer as well as on water repellency was tested. The best results of embossing were achieved by applying pressure of 10 kg/cm 2 for 2 min at 170 °C. In this case, flattening of a natural PTFE roughness and pretty accurate deep replicas of the stamp patterns were observable on the whole imprinted area. Improvement in water repellency was largest for the samples imprinted by Ni stamp patterned with a 2D array of 2 μm square pits spaced by the same dimension and having a depth of 1.5 μm. Cassie–Baxter wetting regime was observed for the deepest imprints with water contact angles up to the superhydrophobic limit.