Elaboration of submicron periodic structures on polymer surfaces by femtosecond laser
Résumé
Modification of surface with ultra-short laser pulses provides special functions for irradiated materials. It is possible to functionalize surfaces through the creation of a multi-scale topography to change some surface properties such as: wettability [1], adhesion [2] and friction [3]. The interest of these ultra-short pulses (130fs) is linked to the possibility to generate new types of self-organized micro / nano surface structures. This study focuses on two polymers: poly (ether ether ketone) or PEEK, under semi- crystalline and amorphous forms and polyimide almost amorphous (PI). Both materials exhibit excellent thermal, mechanical and chemical characteristics over wide temperature ranges. Polyimide is commonly used for optoelectronic applications and PEEK is now essential in the field of biomedical [4]. Polymer surfaces were treated locally by performing a matrix of laser impacts to highlight the influence of crystanillity in ultra-short laser interaction. The different surface morphologies or ripples were analysed by AFM (Atomic Force Microscopy), then their spatial frequency (Δ) has been evaluated. We established a map of presence of these different morphologies according to the laser fluence and pulse number applied [5]. In the case of polyimide, fine ripples (Δ≈165nm) are perpendicular to the beam polarization seem appearing for low values (laser fluence*pulse number). These structures overlap with nano ripples and create a multi-scale of P N topography. Furthermore regularity of ripples differs from one polymer to another for the same laser parameters and seems to depend on the presence of topographical surface defects and rate of crystallinity. This work revealed topographical informations on the local behaviour of the irradiated material. [1]Wang Z-K., Zheng H-Y, Investigation on femtosecond laser irradiation energy in inducing hydrophobic polymer surfaces, Applied Surface Science, vol 257, 10427-10433, (2011). [2]Kwak M-K., Jeong H-E., Bio-inspired slanted polymer nanohairs for anisotropic wetting and directional dry adhesion, Soft Matter, vol 6, 1849-1857, (2010). [3]Etsion I, State of art in laser surface texturing, Journal of Tribology, vol. 127, 248-253, (2005). [4] Kraft M, Koch DK, An investigation into PEEK-on-PEEK as a bearing surface candidate for cervical total disc replacement, The Spine Journal, 603-611, (2012). [5] Dieter Baüerle, Laser Processing and chemistry: Instabilities and Structure formation, (Springer), Chap 28, (2000).