Biomimetics in thin film design – Wrinkling and fracture of pulsed laser deposited films in comparison to human skin

• Published in: Surface & coatings technology 2013-01, Vol.215, p.192-198
• Main Authors: Lackner, J.M., Waldhauser, W., Major, R., Major, L., Hartmann, P.
• Format: Article
• Language: English
• Subjects: Applied sciences; Biomimetics; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Film stress; Fractures; Human skin; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Methods of deposition of films and coatings; film growth and epitaxy; Nanowrinkling; Physics; Production techniques; Surface treatment; Surface treatments
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2012.08.080

The goal of the current work is the biomimetic comparison of wrinkling effects on the nano- and micrometer scale in thin films and on the micro- and millimeter scale of human skin. Ti, Ag, Au, W, C, and TiN thin films with 10 to 500nm thickness were deposited by pulsed laser deposition (PLD) on smooth polyurethane, polycarbonate, polyamide 6, and polyimide polymer substrates. Such high energetic conditions like in PLD plasma lead to stiffening of the polymer surface layers by pseudodiffusion during the initial stages of film growth. Both the high intrinsic film stresses due to high energetic film growth and the huge difference in elastic properties of films and polymer substrates result in hierarchical and self-adapting nanowrinkling phenomena. Intrinsic stresses are a reason for the hierarchical and self-adapting wrinkling of human skin too, being mechanically treated quite similar to the coated polymers as a hard layer (stratum corneum) on a soft foundation (viable epidermis and dermis). Mechanically, the wrinkles have high impact on the elongation behavior: In the elastic region of the stress–strain curve, they are smoothing out at increasing strain. In fracturing, the wrinkles are an origin of cracking (channeling cracks) and afterwards fragmentation of both thin film and stratum corneum islands, respectively, as proofed with in-situ tensile straining experiments of the thin films in scanning electron microscopy. ► Biomimetical comparison of coated polymers and human skin. ► Wrinkling on nano and micron scale. ► Deformation and fracture controlled by wrinkles.