Physchem, Volume 4, Issue 3 (September 2024) – 10 articles

The partition coefficients of seven low molecular weight compounds were tested in different aqueous two-phase systems. The ionic composition of each system included specific salt additives, and it was found that there is a linear relationship between the solute partition coefficients and the presence of different salt additives. The study suggests that the solute structure and the type of ions influence the solute response to the ionic environment. Additionally, it was observed that the solutes’ polar surface area and the solvent-accessible surface area are the essential structural features governing partitioning in aqueous two-phase systems. Full article

Tutton salts form an isomorphic crystallographic family that has been intensively investigated in recent decades due to their attractive thermal and optical properties. In this work, we report four mixed Tutton crystals (obtained by the slow solvent evaporation method) with novel chemical compositions based on K₂V_1−xM’_x(SO₄)₂(H₂O)₆, where M’ represents Co, Ni, Cu, and Zn, aiming at thermochemical energy storage applications. Their structural and thermal properties were correlated with theoretical studies. The crystal structures were solved by powder X-ray diffraction using the Rietveld method with similar compounds. All of the samples crystallized in monoclinic symmetry with the P2₁/a-space group. A detailed study of the intermolecular interactions based on Hirshfeld surfaces and 2D fingerprint mappings showed that the main interactions arise from hydrogen bonds (H∙∙∙O/O∙∙∙H) and dipole–ion (K∙∙∙O/O∙∙∙K). On the other hand, free space percentages in the unit cells determined by electron density isosurfaces presented low values ranging from 0.53 (V–Ni) to 0.81% (V–Cu). The thermochemical findings from thermogravimetry, a differential thermal analysis, and differential scanning calorimetry indicate that K₂V_0.47Ni_0.53(SO₄)₂(H₂O)₆ salt is the most promising among mixed salts (K₂V_1−xM’_x(SO₄)₂(H₂O)₆) for heat storage potential, achieving a low dehydration temperature (≈85 °C), high dehydration enthalpy (≈360 kJ/mol), and high energy storage density (≈1.84 GJ/m³). Full article

One of the most important challenges in polymer science is a rigorous understanding of the molecular mechanisms of rubber elasticity by relating macroscopic deformation to molecular changes and deriving the constitutive stress–strain equation for the elastomeric network. The models developed from the last century to today describe many aspects of the physics of rubber elasticity; although these theories are successful, they are not complete. In this review we analyze the main theoretical and phenomenological models of rubber elasticity, including their assumptions, main characteristics, and stress–strain equations. Then, we compare the predictions of the theories to our experimental data of polydimethylsiloxane (PDMS) rubber, in order to highlight the goodness of the reviewed models. The nonaffine and phenomenological deformation models verify the experimental curves in tension and compression in the whole investigated deformation range $\lambda \le 2$. On the contrary, the affine deformation hypothesis is rigorously verified only in the deformation range $\lambda \le 1$. Full article

Asphalt pavements make up a majority of the essential transportation systems in the US. Asphalt mixtures age and degrade over time, reducing the pavement performance. Pavement performance critically depends on the aging of asphalt binder. The aging of asphalt binder during construction is traditionally modeled by rolling thin film oven (RTFO) testing, while aging during service life is modeled by pressure aging vessel (PAV) testing. Comparing these models to the aging of binders in actual pavements is limited because, to be used for current testing, binders must be separated from the pavement’s aggregate by solvent extraction. Solvent extraction will, at least in part, compromise the structural integrity of asphalt binder samples. Spin-lattice NMR relaxometry has been shown to nondestructively evaluate asphalt properties in situ through the analysis of hydrogen environments. The molecular mobility of hydrogen environments and with it the stiffness of asphalt binder samples can be determined by characteristic T₁ relaxation times, indicating the complexity of asphalt-binder aging. In this study, two laboratory-generated asphalt mixtures, a failed field sample, and several laboratory-aged binder samples are compared by NMR relaxometry. NMR relaxometry was found to be able to differentiate between asphalt samples based on their binder percentage. According to the relaxometry findings, the RTFO binder aging compared favorably to the 6% laboratory-mixed sample. The PAV aging, however, did not compare well to the relaxometry results found for the field-aged sample. The amount of aggregate was found to have an influence on the relaxation times of the binder in the mixed samples and an inverse proportionality of the binder content to the primary NMR relaxation time was detected. It is concluded that molecular water present in the pores of the aggregate material gives rise to such a relationship. The findings of this study lay the foundation for nondestructive asphalt performance evaluation by NMR relaxometry. Full article

The design of an antimicrobial coating material has become important in the prevention of infections caused by the transmission of pathogens coming from human contact with contaminated surfaces. With that aim, layered single hydroxides (LSHs) and layered double hydroxides (LDHs) containing Zn and Cu intercalated with antimicrobial molecules were synthesized and characterized. Cinnamate and salicylate anions were chosen because of their well-known antimicrobial activity. Several coatings based on polyvinyl alcohol (PVA) and LDHs or LSHs with increasing amounts of filler were prepared and filmed on a polyethylene terephthalate (PET) substrate. The coatings were characterized, and their antimicrobial activity was evaluated against several pathogens that are critical in nosocomial infections, showing a synergistic effect between metal ions and active molecules and the ability to inhibit their growth. Full article

In this study, a steady-state thermodynamic equilibrium evaluation of CO₂ methanation was conducted. Calculations were performed by solving the material balance equations using the equilibrium constants of CO₂ methanation and reverse water–gas shift reactions. Results obtained from an analytical method developed with the aid of the Microsoft Excel platform were compared to simulations conducted using the commercially available free software COCO and DWSIM. The effects of temperature, pressure, and H₂/CO₂ ratio on CH₄ yield, carbon oxide formation, and heat balance were investigated. The results indicate that the methanation process is highly favored by low temperatures and higher pressures with a stoichiometric H₂/CO₂ ratio. Under these conditions, CH₄ output increases, and carbon formation is reduced, resulting in better performance. Simulations from all three models are in agreement, with minor differences noted in the DWSIM software. Full article

This review focuses on a set of studies about functional bakery products. The literature search was performed on scientific databases ScienceDirect, PubMed, MDPI, BOn, and SciELO, based on some eligibility criteria, and a total of 102 original research articles about functional bakery products were selected. The studies were analysed according to the types of products, functional properties, functional ingredients, their sources, and the types of measurements described. Results showed that breads were the most frequently analysed products. Most of the products were rich in fibre and antioxidants or were gluten-free. Of the 102 studies, 92 analysed physical properties, 81 involved chemical analyses, 50 involved sensorial analyses, and eight reported microbiological analyses. The most frequent physical properties were texture and colour, while the most frequent chemical components were fibre and minerals. For sensorial properties, colour and texture were particularly evaluated, which were also the most frequently measured physical properties. The studies presented various successful strategies for the fortification of bakery products with functional components, demonstrating their ability to meet consumer needs and potentiate industry growth. This review highlights the relevance of functional bakery products in the current food panorama, contributing to increased knowledge and stimulating discussions about the impact of functional bakery products in promoting healthier eating. Full article

Porous silica-based adsorbents for hexavalent chromium (Cr(VI)) ion removal were prepared by the combined use of functionalization with (3-glycidyloxypropyl)trimethoxysilane and the grafting of branched and linear polyethyleneimine (BPEI and LPEI). LPEI was prepared from polyethyloxazolin by hydrolysis with HCl. The preparation of LPEI was identified by NMR measurements and the grafting of BPEI and LPEI on the silica beads was confirmed by an XPS analysis. The Cr(VI) ion adsorption of the obtained BPEI-grafted silica beads (BPEI–silica beads) was investigated as a function of the pH value, the content of amino groups, the temperature, the Cr(VI) ion concentration, and the molecular mass of the grafted BPEI chains. The Cr(VI) ion adsorption at pH 3.0 increased with an increase in the content of amino groups, and the maximum adsorption capacity of 1.06 mmol/g was obtained when the content of amino groups was at 2.17 mmol/g. This value corresponds to 589 mg/g−1.8KPEI, and the adsorption ratio of about 0.5 is a noteworthy result. The data fit to the pseudo-second-order kinetic model, and the suitability of this fitting was supported by the results that the adsorption capacity and initial rate of adsorption increased with the temperature. In addition, the equilibrium data followed the Langmuir isotherm model. These results clearly demonstrate that the Cr(VI) adsorption occurred chemically, or through the electrostatic interaction of protonated amino groups on the grafted BPEI chains with hydrochromate (${\mathrm{H}\mathrm{C}\mathrm{r}\mathrm{O}}_4^{-}$) ions. A higher adsorption capacity was obtained for the silica beads grafted with shorter BPEI chains, and the adsorption capacity of BPEI–silica beads is a little higher than that of linear PEI-grafted silica beads, suggesting that the Cr(VI) ion adsorption is affected by the chain isomerism of PEI (linear and branched) as well as the molecular mass of the grafted PEI chains, in addition to the content of amino groups. The experimental and analytical results derived from this study emphasize that the BPEI–silica beads can be used as an adsorbent for the removal of Cr(VI) ions from an aqueous medium. Full article

Geopolymers are cementitious materials with exceptional mechanical and physical properties, making them suitable for aerospace applications. Considering their excellent performance, the present investigation aims to develop geopolymers with designed physical properties to address some issues in the aerospace industry. In this sense, the influence of the alkaline activator on the final properties was evaluated. For the development of the geopolymers, sodium hydroxide and sodium metasilicate solutions were preparedto obtain the alkaline activator. The synthesis process also consisted of a mixing stage using a mixer to obtain a homogenous paste. After mixing, the curing process consisted of a first thermal treatment at 60 °C for 4 h to evaporate the excess water, avoid excessive contraction, and promote strength at early ages. Subsequently, the geopolymers were left at rest for 28 days until the final properties were achieved. The influence of the solid-to-liquidratio (S/L) on the microstructure of the geopolymers was evaluated. For this purpose, X-ray fluorescence spectrometry, X-ray diffraction, and infrared spectrometry analyses were performed. The results show that the content of the alkaline activator promotes variations inthe presence of different crystalline phases, which is more noticeable as the S/L ratio increases. Likewise, the infrared spectra display peaks at different wavelengths regarding the variations in elemental composition, which are more evident with the changes in the S/L ratio. In addition, physical studies, such as thermal conductivity and resistance to gamma radiation were conducted for different geopolymer compositions. The results indicate that changes in properties are not too sensitive to compositional variations, although slight modifications exist. Finally, these studies are significant as aerospace-focused materials are directly exposed to this kind of phenomena. The designed geopolymers have to be able to resist and maintain their properties through exposure to any energy. Full article

This study explores the synthesis and application of Pd-doped CuO-ZnO composites for the simultaneous photodegradation of anionic and neutral dyes. The nanocomposite was synthesized using a hydrothermal technique and characterized using XRD, FTIR, and UV-Vis absorption spectra. Photocatalytic degradation experiments were conducted with varying catalyst loadings, revealing optimal conditions for enhanced degradation performance. The nanocomposite exhibited a synergistic effect on the degradation of the dye mixture, following pseudo-first-order kinetics with significant efficiency under sunlight exposure. Moreover, the study evaluated the influence of pH on the degradation process, showing improved efficiency in neutral and basic conditions. Overall, the findings highlight the efficacy of the Pd-doped CuO-ZnO catalyst in degrading complex dye mixtures, offering potential applications for wastewater treatment in various industrial settings. Full article