Physchem, Volume 5, Issue 4 (December 2025) – 6 articles

This study investigates the impact of vibration frequency on the performance of a 10-cell open-cathode direct methanol fuel cell (OC-DMFC) stack. Experiments were conducted using three different vibration frequencies (15, 30, and 60 Hz) and compared against a baseline condition without vibration. Performance was evaluated under varying methanol–water fuel flow rates (1, 5, 25, and 50 mL·min⁻¹) while maintaining constant operating conditions: methanol temperature at 70 °C, methanol concentration at 1 M, and cathode air flow velocity at 4.8 m·s⁻¹. The optimal performance was observed at a fuel flow rate of 5 mL·min⁻¹, where the maximum power density reached 26.05 mW·cm⁻² under 15 Hz vibration—representing a 14% increase compared to the non-vibrated condition. These findings demonstrate that low-frequency vibration can enhance fuel cell performance by improving mass transport characteristics. Full article

Polyethylene terephthalate (PET) films were modified by direct fluorination using fluorine gas at room temperature and 660 torr for reaction times ranging from 10 min to 5 h. Some of the fluorinated samples were dried at 70 °C for 7 days. FT-IR and XPS analyses confirmed the successful incorporation of fluorine into the PET structure, with the formation of -CHF- and -CF₂- groups. The degree of fluorination increased with the reaction time, but excessive reaction led to the formation and loss of CF₄. Drying further decreased the fluorine content due to the continued CF₄ formation. XRD revealed that fluorination increased the crystallinity of PET owing to increased polarity, whereas drying decreased the crystallinity owing to increased crosslinking. The DSC results showed an increase in the glass transition temperature (T_g) after fluorination and drying, which was attributed to increased polarity and crosslinking, respectively. The surface hydrophilicity of PET increased significantly with fluorination time, and the water contact angle decreased to as low as 3.35°. This was due to the introduction of polar fluorine atoms and the development of a rough and porous surface morphology, as observed by AFM. Interestingly, drying of the fluorinated samples led to an increase in the water contact angle, with a maximum of 85.95°, owing to increased crosslinking and particle formation on the surface. This study demonstrates a simple and effective method for controlling the hydrophilicity and hydrophobicity of PET surfaces via direct fluorination and drying. Full article

Ultrasonication offers a safer, lower-temperature method for synthesizing zinc oxide nanoparticles (ZnO-NPs). This study details the development of a pectin-glycerol bionanocomposite film reinforced with ZnO-NPs produced using the top-down ultrasonication method. ZnO-NPs were fabricated with varying ultrasonication durations (0, 30, and 60 min) and the addition of pectin as a capping agent. Extended ultrasonication duration resulted in smaller particle size and more defined morphology. Bionanocomposite films were prepared using the solvent casting method by incorporating ZnO-NPs (0, 0.5, 1, 2.5% w/w) and glycerol (0, 10, 20% w/w) as a plasticizer to a pectin base. The inclusion of ZnO-NPs and glycerol did not affect the shear-thinning behavior of the film-forming solution. FTIR analysis indicated interactions between ZnO-NPs, glycerol, and pectin. The addition of ZnO-NPs and glycerol reduced tensile strength but increased flexibility. ZnO-NPs improved barrier and thermal properties by reducing water vapor permeability and increasing melting point, whereas glycerol lowered glass transition temperature, thus enhancing film flexibility. The best film performance was observed with a combination of 0.5% ZnO and 20% glycerol. These results highlight the effectiveness of the top-down ultrasonication method as a sustainable approach for ZnO-NPs fabrication, supporting the development of pectin/ZnO-NPs/glycerol films as a promising material for eco-friendly packaging. Full article

Over the past decade, two-dimensional materials have become a research hotspot in chemistry, physics, materials science, and electrical and optical engineering due to their excellent properties. Graphene is one of the earliest discovered 2D materials. The absence of a bandgap in pure graphene limits its application in digital electronics where switching behavior is essential. In the present study, researchers have proposed a variety of methods for tuning the graphene bandgap. Machine learning methodologies have demonstrated the capability to enhance the efficiency of materials research by automating the recording of characteristic parameters from the discovery and preparation of 2D materials, property calculations, and simulations, as well as by facilitating the extraction and summarization of governing principles. In this work, we use first principle calculations to build a dataset of graphene band gaps under various conditions, including the application of a perpendicular external electric field, nitrogen doping, and hydrogen atom adsorption. Support Vector Machine (SVM), Random Forest (RF), and Multi-Layer Perceptron (MLP) Regression were utilized to successfully predict the graphene bandgap, and the accuracy of the models was verified using first principles. Finally, the advantages and limitations of the three models were compared. Full article

Gellan gum (Gellan), a versatile polysaccharide applied in gel formation and prebiotic formulations, is often processed to tailor its molecular properties. Previous studies employed gamma irradiation and chemical hydrolysis, though without addressing systematic scaling behavior. This study investigates the structural and conformational modifications of Gellan in dilute aqueous salt solutions using a safer and eco-friendly approach: atmospheric low-dose electron beam (e-beam) degradation coupled with viscosity analysis. Native and E-beam-treated Gellan samples (0.05 g/cm³ in 0.1 M KCl) were examined by relative viscosity at varying temperatures, with intrinsic viscosity and molar mass determined via Solomon–Ciuta and Mark–Houwink relations. Molar mass degradation followed first-order kinetics, yielding rate constants and degradation lifetimes. Structural parameters, including radius of gyration and second virial coefficient, produced scaling coefficients of 0.62 and 0.15, consistent with perturbed coil conformations in a good solvent. The shape factor confirmed preservation of an ideal random coil structure despite irradiation. Conformational flexibility was further analyzed using theoretical models. Transition state theory (TST) revealed that e-beam radiation lowered molar mass and activation energy but raised activation entropy, implying reduced flexibility alongside enhanced solvent interactions. The freely rotating chain (FRC) model estimated end-to-end distance (R_θ) and characteristic ratio (C_∞), while the worm-like chain (WLC) model quantified persistence length (l_p). Results indicated decreased R_θ, increased l_p, and largely unchanged C_∞, suggesting diminished chain flexibility without significant deviation from ideal coil behavior. Overall, this work provides new insights into Gellan’s scaling laws and flexibility under aerobic low-dose E-beam irradiation, with relevance for bioactive polysaccharide applications. Full article

Thermal management in heat exchangers is crucial in many industrial, medical, and scientific applications. However, reducing dependency on active energy sources still represents a substantial challenge. In this context, phase change materials (PCMs) offer an effective solution due to their ability to store and release large amounts of latent heat, assisting in passive thermal management. Therefore, this study proposes the use of RT42 PCM inside a box-type shell-and-tube configuration to establish the relationship between flow rate and charging and discharging behavior of PCM. In the proposed system, heat transferring fluid (HTF) water is circulated in the internal tubes at 60 °C, where the temperature is monitored by a series of thermocouples strategically placed inside the box-type configuration. To evaluate the effect of the flow of HTF on the thermal behavior of the PCM, the charging (melting) and discharging (solidification) analysis is performed by varying the water flow rate at three levels: 1.2, 0.8, and 0.4 L/min inside the laminar region (Re < 2300). A thermal camera and two webcams were used to assess the surface temperature distribution and PCM response, respectively. It was determined that increasing the flow rate accelerates charging and discharging with fluctuations in temperature curves during melting. Full article