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 Force Microscopy, 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 Nanomechanical Mapping. 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.
Highlights
Polymers are widely used in many different fields due to their versatility and reasonable price-performance ratio
Polymers 2020, 12, 1090 of them: (i) fabrication of nanocomposites by in-situ polymerization [3,4], where a small amount of a nanomaterial is added to a polymeric matrix giving the resulting material some of the remarkable properties of the nanomaterial; and (ii) surface nanostructuring, where nanostructures are generated on the surface of a material, which can be engineered to change wettability, adhesion, surface energy, tribological properties and other physicochemical properties [5,6]
Laser Induced Periodic Surface Structures (LIPSS) emerge for fluences below the ablation threshold of the materials, from 15.9 to 31.3 mJ/cm2 for Poly(trimethylene terephthalate) (PTT), and from 19.1 to 33.9 mJ/cm2 for PTT-WS2, conditioned by the number of pulses (500–10,000)
Summary
Polymers are widely used in many different fields due to their versatility and reasonable price-performance ratio. Some specific applications, such as their use as biomaterials [1], protective coatings [2], and in thin film technology to name a few, require polymers with enhanced properties. One can find applications in electronics, packaging, biotechnology and many others [1,2,7]. They are lighter than conventional composites, and their properties can be tailored by changing the additive and the polymer used, the percentage of additive, and the diffusion of the additive in the polymeric matrix [3]
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