Carlos Alberto Brito da Silva Júnior

Graphene-based materials have attracted considerable interest for molecular adsorption, chemical sensing, and protective applications because of their extended π-conjugated electronic structure and ability to interact with aromatic compounds. Herein, a comparative first-principles investigation was performed on the adsorption of eugenol (C10H12O2) and methyleugenol (C11H14O2) on coronene (C24H12), employed as a simplified finite molecular model of a local graphene-like surface. Density functional theory calculations were performed using the ωB97X-D3/6–31G(d) approach, complemented by alternative functionals and the def2-TZVPD basis set to assess basis-set effects and basis set superposition error (BSSE). Both molecules preferentially adopted parallel configurations relative to the coronene surface, with adsorption distances characteristic of physisorption. The uncorrected adsorption energies were −0.645 and −0.672 eV for eugenol and methyleugenol, respectively, whereas BSSE-corrected benchmark calculations with def2-TZVPD yielded values between −0.536 and −0.593 eV. Energy decomposition analysis (EDA) identified dispersion as the dominant stabilizing contribution, followed by electrostatic and orbital interactions. Charge-transfer, molecular electrostatic potential, frontier molecular orbital, and density-of-states analyses revealed weak electronic coupling and limited charge redistribution upon adsorption. Vibrational calculations showed no imaginary frequencies and only minor changes in IR and Raman features, supporting the stability and predominantly noncovalent character of the complexes. Overall, methylation of the phenolic hydroxyl group produced a small increase in adsorption strength within the coronene model without changing the same physisorption mechanism. These results provide molecular-level insights into phenylpropanoid interactions with graphene-like carbon surfaces.

In this study, thermoplastic arrowroot starch (TPA) films cross-linked with citric acid (CA) were prepared using solvent casting method. Different glycerol (25%, 30%, and 35%) and CA (5%, 9%, and 12%) contents were evaluated. The films were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD), as well as by their transparency, thickness, mechanical properties, swelling, moisture content, solubility, water vapor permeability, and soil degradation. FTIR results showed the formation of ester linkages, confirming the cross-linking of arrowroot starch with CA. XRD revealed broad peaks at approximately 20° for all films, characteristic of the amorphous phase of starch. The SEM micrographs revealed more homogeneous and continuous surfaces in the cross-linked films. For films with 30% glycerol, cross-linking increased the tensile strength from 1.74 MPa for the glycerol-free film (TPA-30/CA-0) to 6.60 MPa for the film with 9% CA (TPA-30/CA-9). Additionally, the CA-cross-linked TPA films exhibited less swelling in water for all the evaluated periods. In the soil degradation test, TPA films with CA exhibited slower degradation, with total degradation observed after 18 days. Bread stored with TPA-30/CA-9 and TPA-25/CA-12, exhibited a delay in fungal growth. Thus, based on our results, the TPA-30/CA-9 film presents a suitable potential for use in the food packaging sector.

This study presents a three-dimensional computational fluid dynamics (CFD) investigation of a flanged conical diffuser, focusing on the aerodynamic benefits of integrating an inlet nose geometry. Simulations were conducted in Ansys 2019 R3 using the SST k–ω turbulence model with non-linear eddy viscosity corrections to capture flow separation and reattachment. Validation against experimental data showed excellent agreement for the baseline case. The nosed configuration yielded marked improvements: higher peak velocity ratios, increased maximum pressure coefficients, and enhanced overall pressure recovery. Flow-field analysis revealed that the inlet nose effectively mitigates adverse pressure gradients, delays boundary layer separation, and weakens recirculation zones. Turbulence kinetic energy was significantly reduced near walls and in the core region, indicating lower energy dissipation. Overall, the results demonstrate that the nose geometry functions as an efficient passive flow control device, offering substantial aerodynamic gains for diffuser-augmented wind turbines and other renewable energy systems.

The present study aimed to produce and characterize corn starch/carboxymethyl cellulose (TPC/CMC) films cross-linked with different concentrations of citric acid (CA). The films were obtained by solvent evaporation (casting solution) with 5, 10, 15, and 20% citric acid relative to the CMC mass (TPC/CMC-CA-0 to 20). They were qualitatively evaluated for visual aspects, swelling, moisture content, and solubility, and characterized by Fourier transform infrared spectroscopy (FTIR), thickness, and scanning electron microscopy (SEM). The results allowed us to evaluate the cross-linking effect promoted by citric acid. Visually, all films showed excellent optical transparency. FTIR spectroscopy demonstrated the formation of ester groups, indicative of cross-linking of the TPC-CMC films. SEM images revealed a homogeneous surface morphology without porosity in the films with CA. The addition of CA to the TPC-CMC films reduced water swelling, moisture absorption, and permeation. Additionally, the insertion of citric acid promoted an improvement in the tensile strength of TPC-CMC from 6.07 to 8.39 MPa for TPC-CMC/CA-15. This same trend was obtained with an increase of around 115% for the modulus in the TPC-CMC/CA-15 film compared to the film without CA. These results were due to cross-linking promoted by CA which produces a more cohesive material and thus increases the modulus and tensile strength. Thus, our results demonstrate that the cross-linking promoted by CA in TPC-CMC films has a profound influence on their water susceptibility and tensile properties.

The development of antimicrobial resistance against traditionally used drugs has become a current problem. To address these problems, essential oil emulsions have emerged as one of the solutions. Emulsions, however, may exhibit instability phenomena due to storage time. This study investigated the influence of storage time on the physicochemical properties of cinnamon bark essential oil emulsions. These emulsions were produced using: cinnamon bark essential oil (Cinnamomum cassia) (CEO), coconut oil as the Ostwald ripening inhibitor (OR), and 10 and 20 % (v/v) of polysorbate 80 (CEOE-1 and CEOE-2, respectively) as the surfactant by spontaneous emulsification. The visual appearance of emulsions CEOE-1 and CEOE-2 were evaluated at 0, 15, and 30 days. For these emulsions, the physicochemical properties investigated were: pH, turbidity, and dynamic viscosity at 0, 15 and 30 days. Dynamic light scattering results revealed that the average particle size for CEOE-1 and CEOE-2 are in nanometric dimensions, 176.79 ± 3.13 nm and 182.53 ± 1.47 nm, respectively. Our results demonstrated marginal variations in the physicochemical properties of CEOE-2 at 0, 15 and 30 days. In addition, the antimicrobial activity against Escherichia coli and Candida albicans was found for CEOE-1 and CEOE-2, but not to Staphylococcus aureus.

Resumo Os nanotubos de carbono de parede simples (NCPS) representam uma classe de materiais que tem propriedades eletrônicas distintas e potenciais aplicações em nanoeletrônica. Este artigo apresenta um estudo comparativo das propriedades eletrônicas e transporte de NCPS utilizando três métodos: (i) Tight-Binding (T-B): método teórico aplicado a grafeno com condições de contorno em NCPS implementado via software Maple 12.0, (ii) DFT: método computacional de NCPS hidrogenados de tamanho finito via software HyperChem 7.0 e (iii) DFT+NEGF: método computacional das propriedades eletrônicas/transporte via software SIESTA/TranSIESTA. Os resultados mostraram que todos os métodos são eficazes na descrição detalhada das propriedades eletrônicas e transporte de NCPS. Em T-B, o comportamento eletrônico tem dependência com índice de Hamada (m,n) para NCPS armchair (m, m), NCPS zigzag (m, 0) e NCPS quiral (m, n), isto é, semicondutor (m − n ≠ 3q) ou metálico (m − n = 3q). Com DFT, NCPS hidrogenados mostraram abertura de gap em NCPS metálicos, exibindo transição metal-semicondutor. Em DFT+NEGF, os NCPS Zigzag exibiram característica elétrica de transistor de efeito de campo. A novidade deste trabalho é apresentar um estudo comparativo sistemático e didático entre T-B, DFT e DFT+NEGF aplicados a NCPS, combinando métricas físicas com uma avaliação prática de custo computacional e orientações pedagógicas para uso em ensino e treinamento.

Research on new materials for wound care plays a key role in advancing biomaterials. The present study focused on the elaboration and characterization of polyvinyl alcohol /chitosan (BP) membranes in a ratio of 0.2/0.8 (m/m), with the addition of copaiba oil emulsion and silver nanoparticles (AgNPs), using the casting technique. The nanoparticles were evaluated by UV/Vis spectroscopy and Transmission Electron Microscopy (TEM), while the films were analyzed by Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy, and swelling, humidity, and contact angle. UV/Vis findings exhibited the characteristic absorption of AgNPs. The films containing 0.5% copaiba oil emulsion exhibited rough surfaces and few droplets. FTIR spectra indicated the presence of caryophyllene in the membranes at 860 cm-1. The samples demonstrated high fluid absorption capacity, with the BP membrane presenting the highest average hydrophilic contact angle (74.53° in PBS). The humidity content of the BP with 0.5 mL of copaiba oil and AgNPs (BP/AgNPs-0.5) membrane was considerable, with an average of 90.24 %. The results indicate that the BP/AgNPs-0.5 films have great potential for wound care applications.

We use density-functional theory combined with nonequilibrium Green's functions (DFT+NEGF) to characterize electronic transport in net-τ nanoribbons and to identify concrete device-relevant metrics.