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- Influence of femtosecond laser surface nanotexturing on the friction behavior of silicon sliding against PTFEPublication . Alves-Lopes, Isabel; Almeida, Amélia; Oliveira, Vítor; Vilar, RuiThe aim of the present work was to investigate the influence of laser-induced periodic surface structures (LIPSS) produced by femtosecond laser on the friction behavior of silicon sliding on polytetrafluoroethylene (PTFE) in unlubricated conditions. Tribological tests were performed on polished and textured samples in air using a ball-on-flat nanotribometer, in order to evaluate the friction coefficient of polished and textured silicon samples, parallel and perpendicularly to the LIPSS orientation. In the polished specimens, the friction coefficient decreases with testing time at 5 mN, while it increases slightly at 25 mN. It also decreases with increasing applied load. For the textured specimens, the friction coefficient tends to decrease with testing time in both sliding directions studied. In the parallel sliding direction, the friction coefficient decreases with increasing load, attaining values similar to those measured for the polished specimen, while it is independent of the applied load in the perpendicular sliding direction, exhibiting values lower than in the two other cases. These results can be explained by variations in the main contributions to friction and in the wear mechanisms. The influence of the temperature increase at the interface and the consequent changes in the crystalline phases of PTFE are also considered.
- Processing of poly(ionic liquid)-ionic liquid membranes using femtosecond (fs) laser radiation: Effect on CO2 separation performancePublication . Gouveia, Andreia S.L.; Oliveira, Vitor; Ferraria, Ana Maria; Rego, Ana; Ferreira, Maria João; Tomé, Liliana C.; Almeida, Amélia; Marrucho, I. M.Femtosecond (fs) laser micromachining on polymeric materials is a single-step, and contactless manufacturing technology. Knowing the potential of poly(ionic liquid)s (PILs) and their derived composite materials incorporating ionic liquids (PIL-IL) to design membranes with improved CO2 separation, we here explore for the first time the creation of microchannels on the surface of PIL-IL materials by laser ablation using femtosecond laser radiation. PIL-IL membranes composed of pyrrolidinium-based PILs containing the [NTf2](-) and [C(CN)(3)](-) anions and different amounts of their corresponding ILs (40 and 60 wt%) were prepared and micromachined using fs laser pulses varying the pulse repetition rate, scanning speed, and pulse energy. The morphology of the fs laser modified PIL-IL samples was investigated through scanning electron microscopy (SEM), while the influence of the fs laser processing on the membranes structure was analyzed by solid-state nuclear magnetic resonance (ssNMR), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The CO2/N-2 and CO2/H-2 separation performances of the irradiated membranes were also evaluated and compared to those of the non-irradiated. Depending on the parameters used, fs laser processing was successful in modifying the surface of PIL-IL membranes through the formation of microchannels around 55-60 mu m deep. Significant improvements in CO2, N-2 and H-2 permeabilities were achieved for the irradiated PIL-IL membranes, maintaining their CO2/N-2 and CO2/H-2 permselectivities.
- Strategy to improve the mechanical properties of bioabsorbable materials based on chitosan for orthopedic fixation applicationsPublication . Figueiredo, Lígia; Fonseca, Rita; Pinto, Luís F. V.; Ferreira, Frederico Castelo; Almeida, Amélia; Rodrigues, AlexandraBioabsorbable polymeric fixation devices have been used as an alternative to metallic implants in orthopedics, preventing the stress shielding effect and avoiding a second surgery for implant removal. However, several problems are still associated with current bioabsorbable implants, including the limited mechanical stiffness and strength, and the adverse tissue reactions generated. To minimize or even eliminate the problems associated with these implants, strategies have been developed to synthesize new implant materials based on chitosan. To overcome the brittle behavior of most 3D chitosan-based structures, glycerol and sorbitol were blended to chitosan and the effect of these plasticizers in the produced specimens was analyzed by flexural tests, Berkovich tests, scanning electron microscopy (SEM) and micro-CT analyzes. The improvement of the mechanical properties was also tested by adding ceramics, namely hydroxyapatite powder and biphasic mixtures of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP). In the plasticizers group, the best combination of the measured properties was obtained for chitosan with 10% glycerol (flexural strength of 53.8 MPa and indentation hardness of 19.4 kgf/mm(2)), while in the ceramics group the best mechanical behavior was obtained for chitosan with 10% HA+beta-TCP powder (flexural strength of 67.5 MPa and indentation hardness 28.2 kgf/mm(2)). All the tested material compositions were dense and homogeneous, fundamental condition for a good implant performance. These are encouraging results, which support the continued development of chitosan-based materials for orthopedic fixation applications.
- Processing of poly(ionic liquid)-ionic liquid membranes using femtosecond (fs) laser radiation: Effect on CO2 separation performancePublication . Gouveia, Andreia S.L.; Oliveira, Vitor; Ferraria, Ana Maria; Rego, Ana; Ferreira, Maria João; Tomé, Liliana C.; Almeida, Amélia; Marrucho, I. M.Femtosecond (fs) laser micromachining on polymeric materials is a single-step, and contactless manufacturing technology. Knowing the potential of poly(ionic liquid)s (PILs) and their derived composite materials incorporating ionic liquids (PIL-IL) to design membranes with improved CO2 separation, we here explore for the first time the creation of microchannels on the surface of PIL-IL materials by laser ablation using femtosecond laser radiation. PIL-IL membranes composed of pyrrolidinium-based PILs containing the [NTf2](-) and [C(CN)(3)](-) anions and different amounts of their corresponding ILs (40 and 60 wt%) were prepared and micromachined using fs laser pulses varying the pulse repetition rate, scanning speed, and pulse energy. The morphology of the fs laser modified PIL-IL samples was investigated through scanning electron microscopy (SEM), while the influence of the fs laser processing on the membranes structure was analyzed by solid-state nuclear magnetic resonance (ssNMR), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The CO2/N-2 and CO2/H-2 separation performances of the irradiated membranes were also evaluated and compared to those of the non-irradiated. Depending on the parameters used, fs laser processing was successful in modifying the surface of PIL-IL membranes through the formation of microchannels around 55-60 mu m deep. Significant improvements in CO2, N-2 and H-2 permeabilities were achieved for the irradiated PIL-IL membranes, maintaining their CO2/N-2 and CO2/H-2 permselectivities.
- Processing of poly(ionic liquid)-ionic liquid membranes using femtosecond (fs) laser radiation: Effect on CO2 separation performancePublication . Gouveia, Andreia S.L.; Oliveira, Vitor; Ferraria, Ana Maria; Rego, Ana; Ferreira, Maria João; Tomé, Liliana C.; Almeida, Amélia; Marrucho, I. M.Femtosecond (fs) laser micromachining on polymeric materials is a single-step, and contactless manufacturing technology. Knowing the potential of poly(ionic liquid)s (PILs) and their derived composite materials incorporating ionic liquids (PIL-IL) to design membranes with improved CO2 separation, we here explore for the first time the creation of microchannels on the surface of PIL-IL materials by laser ablation using femtosecond laser radiation. PIL-IL membranes composed of pyrrolidinium-based PILs containing the [NTf2](-) and [C(CN)(3)](-) anions and different amounts of their corresponding ILs (40 and 60 wt%) were prepared and micromachined using fs laser pulses varying the pulse repetition rate, scanning speed, and pulse energy. The morphology of the fs laser modified PIL-IL samples was investigated through scanning electron microscopy (SEM), while the influence of the fs laser processing on the membranes structure was analyzed by solid-state nuclear magnetic resonance (ssNMR), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The CO2/N-2 and CO2/H-2 separation performances of the irradiated membranes were also evaluated and compared to those of the non-irradiated. Depending on the parameters used, fs laser processing was successful in modifying the surface of PIL-IL membranes through the formation of microchannels around 55-60 mu m deep. Significant improvements in CO2, N-2 and H-2 permeabilities were achieved for the irradiated PIL-IL membranes, maintaining their CO2/N-2 and CO2/H-2 permselectivities.