Laser-induced periodic surface structuring of poly(trimethylene terephthalate) films containing tungsten disulfide nanotubes

Abstract

We report the study of the formation of Laser Induced Periodic Surface Structures (LIPSS),with UV femtosecond laser pulses (λ = 265 nm), in free-standing films of both Poly(trimethylene terephthalate) (PTT) and the composite PTT/tungsten disulfide inorganic nanotubes (PTT-WS2). We characterized the range of fluences and number of pulses necessary to induce LIPSS formation and measured the topography of the samples by Atomic ForceMicroscopy, the change in surface energy and contact angle using the sessile drop technique, and the modification in both Young's modulus and adhesion force values with Peak Force-Quantitative NanomechanicalMapping. LIPSS appeared parallel to the laser polarization with a period close to its wavelength in a narrow fluence and number of pulses regime, with PTT-WS2 needing slightly larger fluence than raw PTT due to its higher crystallinity and heat diffusion. Little change was found in the total surface energy of the samples, but there was a radical increase in the negative polar component (γ-). Besides, we measured small variations in the samples Young's modulus after LIPSS formation whereas adhesion is reduced by a factor of four. This reduction, as well as the increase in γ-, is a result of the modification of the surface chemistry, in particular a slight oxidation, during irradiation.