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Item High-Tribological-Performance Polymer Nanocomposites: An Approach Based on the Superlubricity State of the Graphene Oxide Agglomerates(MDPI) Ferreira, Eder Henrique Coelho; Vieira, Angela Aparecida; Vieira, Lucia; Fechine, Guilhermino José MacêdoHere, nanocomposites of high-molecular-weight polyethylene (HMWPE) and HMWPE- UHMWPE (80/20 wt.%) containing a low amount of multilayer graphene oxide (mGO) (≤0.1 wt.%) were produced via twin-screw extrusion to produce materials with a higher tribological performance than UHMWPE. Due to the high viscosity of both polymers, the nanocomposites presented a signifi- cant concentration of agglomerates. However, the mechanical (tensile) and tribological (volumetric loss) performances of the nanocomposites were superior to those of UHMWPE. The morphology of the nanocomposites was investigated using differential scanning calorimetry (DSC), microtomogra- phy, and transmission electron microscopy (TEM). The explanation for these results is based on the superlubricity phenomenon of mGO agglomerates. It was also shown that the well-exfoliated mGO also contained in the nanocomposite was of fundamental importance as a mechanical reinforcement for the polymer. Even with a high concentration of agglomerates, the nanocomposites displayed tribological properties superior to UHMWPE’s (wear resistance up to 27% higher and friction co- efficient up to 57% lower). Therefore, this manuscript brings a new exception to the rule, showing that agglomerates can act in a beneficial way to the mechanical properties of polymers, as long as the superlubricity phenomenon is present in the agglomerates contained in the polymer.Item Balancing thermal conductivity, dielectric, and tribological properties in polyamide 1010 with 2D nanomaterials(Willey) Pinto, Gabriel Matheus; Staffa, Lucas; Helal, Emna; Hahn, Carolina; Vieira, Lúcia; Ribeiro, Hélio; David, Eric; Demarquette, Nicole Raymonde; Fechine, Guilhermino José MacêdoLow electrical conductivity and high heat dissipation are crucial for electronic packaging materials. Additionally, friction is critical for the lifespan and energy efficiency of components. To address these requirements, polymer nanocomposites based on bio-based polyamide 1010 and ultra-low contents of 2D nanomaterials were produced by melt-blending. Graphene oxide, hexago- nal boron nitride, and molybdenum disulfide were selected for their two- dimensional structure and electrical insulation, providing high thermal conductivity while preserving the polymer's dielectric nature. Hybrid nanocomposites were also produced to explore potential synergistic effects. Results showed all compositions maintained the polymer's intrinsic dielectric properties. Although the friction coefficient increased slightly compared with neat polyamide, all nanocomposites remained within the low-friction range required for low-friction materials. Thermal conductivity improved by 5%–10% compared with unfilled polyamide, with hybrid systems performing slightly better, indicating a minor synergistic effect. Despite these enhancements being modest compared with the literature, achieving high thermal conductivity usu- ally requires over 20 wt% of nanofiller, which is detrimental to mechanical per- formance. In this study, at most 0.5 wt% was used, with composites being obtained directly through melt-blending. This highlights their potential as low- content additives for thermal interface materials without compromising other essential properties.Item Enhancing UV Radiation Resilience of DLC-Coated Stainless Steel with TiO2: A Dual-Layer Approach(MDPI) Macário, Paulo Fabrício; Silveira, Carolina Hahn da; Vieira, Angela Aparecida Moraes; Marcondes, André Ricardo; Marques, Francisco das Chagas; Fechine, Guilhermino José Macêdo; Vieira, LuciaThis study presents an innovative dual-layer coating approach integrating titanium dioxide (TiO2) onto diamond-like carbon (DLC)-coated 316L stainless steel. The combination of PECVD- deposited DLC and ALD-deposited TiO2 aims to preserve the inherent tribological properties of DLC while mitigating UV-induced degradation. By leveraging the ability of TiO2 to absorb, reflect, and scatter UV light, this dual-layer strategy significantly enhances the durability of DLC coatings in radiation-prone environments. The effects of accelerated aging through UV exposure on DLC and DLC/TiO2 films were evaluated using an Accelerated Weathering Tester. Comprehensive analyses were conducted to assess the structural and mechanical properties before and after UV exposure, including Raman spectroscopy, profilometry, SEM, EDS, nanoindentation, and tribometry. The results demonstrate that the TiO2 layer effectively mitigates UV-induced damage, preserving the DLC film’s integrity and tribological performance even after 408 h of UV aging. Specifically, the DLC/TiO2 coatings maintained lower roughness, higher hardness, and better adhesion than DLC- only coatings under identical conditions. This research significantly advances protective coating technology by enhancing the durability and performance of DLC films, particularly in aerospace and other demanding industries where exposure to UV radiation is a critical concern.