Ruan Roberto Henriques

Poly(lactic acid) (PLA)-based nanocomposites containing a mixture of graphene nanoplatelets (GNP) and carbon nanotube (CNT) as hybrid fillers were prepared using a solution-assisted sonication process followed by melt processing. The effects of the filler dispersion on dielectric properties and microwave absorbing (MWA) performance were systematically investigated. Two ionic liquids (ILs), trihexyl-(tetra-decyl)phosphonium bis (trifluoromethanesulfonyl)imide (IL1) and 11-carboxyundecyl-triphenylphosphonium bromide (IL2), were employed as dispersing agents for the carbonaceous fillers. Incorporation of IL-treated fillers resulted in enhanced dielectric permittivity and improved MWA performance of the PLA composites. The MWA properties were evaluated in X- band and Ku-band. A minimum reflection loss (RL) of −34 dB and an effective absorption bandwidth (EAB) of 2.1 GHz were achieved for the composite containing GNP/CNT/IL2 (HB3) at a weight ratio of 2.5:0.5:0.5 wt% with one 3 mm thick layer. The superior performance of IL2 is attributed to π-π and π-cation interactions between its phenyl-containing cation and the carbonaceous fillers, as well as improved compatibility with the PLA matrix due to carboxyl groups. Additionally, three-layered composite structures, combining PLA/GNP as the outer layer with IL-assisted hybrid fillers in the core and PLA/CNT at the bottom layer, achieved an extended EAB of 4.5 GHz for GNP/HB2/CNT arrangement and 4.35 GHz for the GNP/HB3/CNT arrangement, driven by enhanced scattering and internal reflection of microwaves. These results demonstrate the potential of IL-assisted hybrid filler dispersion in PLA for developing biodegradable materials with multifunctional applications as charge storage capacitors and microwave absorbing materials for sustainable electronics.

Neste estudo, a cinética de aquação do complexo trans-[Co(en)2Cl2]Cl foi investigada na presença do poli(etilenoglicol)-PEG por espectroscopia na região do ultravioleta-vísivel (UV-vis). Especificamente, o efeito da massa molar média do PEG (PEG1500-1500 g.mol-1 e PEG6000-6000 g.mol-1) e de sua concentração sobre a reação de aquação foi estudado. Além disso, a energia de ativação (Ea) foi também determinada para as reações de aquação. Os resultados experimentais mostraram que a constante de velocidade (k) da reação de aquação depende da massa molar média do polímero e de sua concentração. Os valores de Ea obtidos para a aquação do trans-[Co(en)2Cl2]Cl, trans-[Co(en)2Cl2]Cl + PEG1500 (5% m/m) e trans-[Co(en)2Cl2]Cl + PEG6000 (5% m/m) foram de (106 ± 2) kJ.mol-1, (101 ± 1) kJ.mol-1 e (96 ± 2) kJ.mol-1, respectivamente. Estes resultados indicam que os polímeros catalisam a aquação do complexo, sendo este efeito mais pronunciado para o PEG6000. Portanto, os resultados experimentais demonstraram que o PEG pode ser utilizado como catalisador em reações de aquação.

Magnetic ionic liquid (MIL) based on alkyl phosphonium cation was used as a curing agent for developing epoxy nanocomposites (ENCs) modified with a graphene nanoplatelet (GNP)/carbon nanotube (CNT) hybrid filler. The materials were prepared by a solvent-free procedure involving ball-milling technology. ENCs containing as low as 3 phr of filler (GNP/CNT = 2.5:0.5 phr) exhibited electrical conductivity with approximately six orders of magnitude greater than the system loaded with GNP = 2.5 phr. Moreover, the use of MIL (10 phr) resulted in ENCs with higher conductivity compared with the same system cured using conventional aliphatic amine. The filler dispersion within the epoxy matrix was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic interference shielding effectiveness (EMI SE), evaluated in the X- and Ku-band frequency range, revealed a great contribution of the absorption mechanism for the ENC containing the hybrid filler and cured with MIL. Moreover, the best microwave-absorbing response was achieved with the ENC containing GNP/CNT = 2.5/0.5 phr, and cured with ML, which a minimum RL of −23.61 dB and an effective absorption bandwidth of 5.18 GHz were observed for thickness of 1.5 mm. In summary, this system is a promising material for both civilian and military applications due to its simple and scalable nanocomposite preparation method, the lightweight nature of the composites resulting from the low filler content, the commercial availability and cost-effectiveness of GNP, and its high electromagnetic wave attenuation across a broad frequency range.

Alkyl phosphonium‐based ionic liquids (ILs), namely trihexyl(tetradecyl)‐phosphonium chloride (P₆₆₆₁₄Cl), ethyl‐(tributyl)‐phosphonium diethyl phosphate (P₄₄₄₂[dep]), trihexyl(tetradecyl)‐phosphonium bis(trifluorosulfonyl)imide (P₆₆₆₁₄[TFSI]), and trihexyl(tetradecyl)‐phosphonium zinc tetrachloride ([P₆₆₆₁₄]₂[ZnCl₄]) were used for the first time as anticorrosive additives for epoxy coatings on AISI 1020 carbon steel plates. The corrosion protection performance of intact and artificially scratched coatings was evaluated in 3.5 wt% NaCl aqueous solution by electrochemical impedance spectroscopy. Regarding the intact coatings, those containing 0.5 phr of [P₆₆₆₁₄]₂[ZnCl₄] and 1.0 phr of P₆₆₆₁₄[TFSI] and P₄₄₄₂[dep] presented excellent corrosion resistance up to 720 h of immersion with |Z|_f=0.01Hz values higher than 10¹⁰ Ω cm². The scratched coatings loaded with P₄₄₄₂[dep] displayed the best anticorrosive response after 168 h of immersion. Furthermore, these coatings and that loaded with 0.5 phr of [P₆₆₆₁₄]₂[ZnCl₄] displayed an increase of corrosion resistance with increasing the immersion time, suggesting the formation of a passivating layer at the epoxy–substrate interface. The inhibition characteristic of the corresponding anions in the IL component contributes for this behavior. The hydrophobic characteristic of the coatings before and after the immersion in the saline solution was studied by measuring the water contact angle. Furthermore, the adhesion strength after immersion was also investigated by pull‐off testing.