Sign in to use this feature.

Years

Between: -

Subjects

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Journals

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Article Types

Countries / Regions

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Search Results (316)

Search Parameters:
Keywords = relaxation spectra

Order results
Result details
Results per page
Select all
Export citation of selected articles as:
16 pages, 2441 KiB  
Article
Phosphonium Salt-Functionalized β-Cyclodextrin Film for Ultrasensitive and Selective Electrochemical Impedance Spectroscopy Detection of Perchlorate in Drinking Water
by Zeineb Baatout, Achref Jebnouni, Nawfel Sakly, Safa Teka, Nuzaiha Mohamed, Sayda Osman, Raoudha Soury, Mabrouka El Oudi, Salman Hamdan Alsaqri, Nejmeddine Smida Jaballah and Mustapha Majdoub
Polymers 2025, 17(14), 1937; https://doi.org/10.3390/polym17141937 - 15 Jul 2025
Viewed by 377
Abstract
This work represents the first use of a phosphonium salt-functionalized β-Cyclodextrin polymer (β-CDP) as a highly selective sensing membrane for monitoring the safety of drinking water against perchlorate ions (ClO4) using electrochemical impedance spectroscopy (EIS). Structural confirmation via 1H [...] Read more.
This work represents the first use of a phosphonium salt-functionalized β-Cyclodextrin polymer (β-CDP) as a highly selective sensing membrane for monitoring the safety of drinking water against perchlorate ions (ClO4) using electrochemical impedance spectroscopy (EIS). Structural confirmation via 1H NMR, 13C NMR, 31P NMR, and FT-IR spectroscopies combined with AFM and contact angle measurements demonstrate how the enhanced solubility of modified cyclodextrin improves thin film quality. The innovation lies in the synergistic combination of two detection mechanisms: the “Host-Guest” inclusion in the cyclodextrin cavity and anionic exchange between the bromide ions of the phosphonium groups and perchlorate anions. Under optimized functionalization conditions, EIS reveals high sensitivity and selectivity, achieving a record-low detection limit (LOD) of ~10−12 M and a wide linear range of detection (10−11 M–10−4 M). Sensing mechanisms at the functionalized transducer interfaces are examined through numerical fitting of Cole-Cole impedance spectra via a single relaxation equivalent circuit. Real water sample analysis confirms the sensor’s practical applicability, with recoveries between 96.9% and 109.8% and RSDs of 2.4–4.8%. Finally, a comparative study with reported membrane sensors shows that β-CDP offers superior performance, wider range, higher sensitivity, lower LOD, and simpler synthesis. Full article
(This article belongs to the Special Issue Development of Polymer Materials as Functional Coatings)
Show Figures

Figure 1

31 pages, 3723 KiB  
Review
Chemical Profiling and Quality Assessment of Food Products Employing Magnetic Resonance Technologies
by Chandra Prakash and Rohit Mahar
Foods 2025, 14(14), 2417; https://doi.org/10.3390/foods14142417 - 9 Jul 2025
Viewed by 578
Abstract
Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) are powerful techniques that have been employed to analyze foodstuffs comprehensively. These techniques offer in-depth information about the chemical composition, structure, and spatial distribution of components in a variety of food products. Quantitative NMR [...] Read more.
Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) are powerful techniques that have been employed to analyze foodstuffs comprehensively. These techniques offer in-depth information about the chemical composition, structure, and spatial distribution of components in a variety of food products. Quantitative NMR is widely applied for precise quantification of metabolites, authentication of food products, and monitoring of food quality. Low-field 1H-NMR relaxometry is an important technique for investigating the most abundant components of intact foodstuffs based on relaxation times and amplitude of the NMR signals. In particular, information on water compartments, diffusion, and movement can be obtained by detecting proton signals because of H2O in foodstuffs. Saffron adulterations with calendula, safflower, turmeric, sandalwood, and tartrazine have been analyzed using benchtop NMR, an alternative to the high-field NMR approach. The fraudulent addition of Robusta to Arabica coffee was investigated by 1H-NMR Spectroscopy and the marker of Robusta coffee can be detected in the 1H-NMR spectrum. MRI images can be a reliable tool for appreciating morphological differences in vegetables and fruits. In kiwifruit, the effects of water loss and the states of water were investigated using MRI. It provides informative images regarding the spin density distribution of water molecules and the relationship between water and cellular tissues. 1H-NMR spectra of aqueous extract of kiwifruits affected by elephantiasis show a higher number of small oligosaccharides than healthy fruits do. One of the frauds that has been detected in the olive oil sector reflects the addition of hazelnut oils to olive oils. However, using the NMR methodology, it is possible to distinguish the two types of oils, since, in hazelnut oils, linolenic fatty chains and squalene are absent, which is also indicated by the 1H-NMR spectrum. NMR has been applied to detect milk adulterations, such as bovine milk being spiked with known levels of whey, urea, synthetic urine, and synthetic milk. In particular, T2 relaxation time has been found to be significantly affected by adulteration as it increases with adulterant percentage. The 1H spectrum of honey samples from two botanical species shows the presence of signals due to the specific markers of two botanical species. NMR generates large datasets due to the complexity of food matrices and, to deal with this, chemometrics (multivariate analysis) can be applied to monitor the changes in the constituents of foodstuffs, assess the self-life, and determine the effects of storage conditions. Multivariate analysis could help in managing and interpreting complex NMR data by reducing dimensionality and identifying patterns. NMR spectroscopy followed by multivariate analysis can be channelized for evaluating the nutritional profile of food products by quantifying vitamins, sugars, fatty acids, amino acids, and other nutrients. In this review, we summarize the importance of NMR spectroscopy in chemical profiling and quality assessment of food products employing magnetic resonance technologies and multivariate statistical analysis. Full article
(This article belongs to the Special Issue Quantitative NMR and MRI Methods Applied for Foodstuffs)
Show Figures

Figure 1

30 pages, 5294 KiB  
Article
Non-Invasive Bioelectrical Characterization of Strawberry Peduncles for Post-Harvest Physiological Maturity Classification
by Jonnel Alejandrino, Ronnie Concepcion, Elmer Dadios, Ryan Rhay Vicerra, Argel Bandala, Edwin Sybingco, Laurence Gan Lim and Raouf Naguib
AgriEngineering 2025, 7(7), 223; https://doi.org/10.3390/agriengineering7070223 - 8 Jul 2025
Viewed by 309
Abstract
Strawberry post-harvest losses are estimated at 50%, due to improper handling and harvest timing, necessitating the use of non-invasive methods. This study develops a non-invasive in situ bioelectrical spectroscopy for strawberry peduncles. Based on traditional assessments and invasive metrics, 100 physiologically ripe (PR) [...] Read more.
Strawberry post-harvest losses are estimated at 50%, due to improper handling and harvest timing, necessitating the use of non-invasive methods. This study develops a non-invasive in situ bioelectrical spectroscopy for strawberry peduncles. Based on traditional assessments and invasive metrics, 100 physiologically ripe (PR) and 100 commercially mature (CM) strawberries were distinguished. Spectra from their peduncles were measured from 1 kHz to 1 MHz, collecting four parameters (magnitude (Z(f)), phase angle (θ(f)), resistance (R(f)), and reactance (X(f))), resulting in 80,000 raw data points. Through systematic spectral preprocessing, Bode and Cole–Cole plots revealed a distinction between PR and CM strawberries. Frequency selection identified seven key frequencies (1, 5, 50, 75, 100, 250, 500 kHz) for deriving 37 engineered features from spectral, extrema, and derivative parameters. Feature selection reduced these to 6 parameters: phase angle at 50 kHz (θ (50 kHz)); relaxation time (τ); impedance ratio (|Z1k/Z250k|); dispersion coefficient (α); membrane capacitance (Cm); and intracellular resistivity (ρi). Four algorithms (TabPFN, CatBoost, GPC, EBM) were evaluated with Monte Carlo cross-validation with five iterations, ensuring robust evaluation. CatBoost achieved the highest accuracy at 93.3% ± 2.4%. Invasive reference metrics showed strong correlations with bioelectrical parameters (r = 0.74 for firmness, r = −0.71 for soluble solids). These results demonstrate a solution for precise harvest classification, reducing post-harvest losses without compromising marketability. Full article
(This article belongs to the Section Pre and Post-Harvest Engineering in Agriculture)
Show Figures

Figure 1

24 pages, 2997 KiB  
Article
Selective Air Oxidation of Bis- and Trisphosphines Adsorbed on Activated Carbon Surfaces
by Ehsan Shakeri, John C. Hoefler and Janet Blümel
Molecules 2025, 30(13), 2737; https://doi.org/10.3390/molecules30132737 - 25 Jun 2025
Viewed by 260
Abstract
Bis- and trisphosphines incorporating methylene and aryl spacers readily adsorb on the surface of porous activated carbon (AC). The adsorption can be performed in the absence of solvents, even when the phosphines have high melting points, or from solutions. The diverse phosphines Ph [...] Read more.
Bis- and trisphosphines incorporating methylene and aryl spacers readily adsorb on the surface of porous activated carbon (AC). The adsorption can be performed in the absence of solvents, even when the phosphines have high melting points, or from solutions. The diverse phosphines Ph2PCH2PPh2 (dppm), Ph2P(CH2)2PPh2 (dppe), Ph2P(CH2)3PPh2 (dppp), Ph2P(p-C6H4)PPh2 (dppbz), and (Ph2PCH2)3CCH3 (tdme) were adsorbed in submonolayers on AC. The adsorbed phosphines were studied by 31P MAS (magic angle spinning) NMR spectroscopy, and their mobilities on the surface were confirmed by determining the 31P T1 relaxation times. All phosphine groups of each bis- and trisphosphine molecule are in contact with the surface, and the molecules exhibit translational mobility as one unit. All phosphines used here are air-stable. Once a submonolayer is created on the AC surface, oxygen from the air is co-adsorbed and transforms all phosphines quantitatively into phosphine oxides at room temperature. The oxidation proceeds in a consecutive manner with the oxidation of one phosphine group after another until the fully oxidized species are formed. Studies of the kinetics are based on integrating the signals in the solution 31P NMR spectra. High temperatures and low surface coverages increase the speed of the oxidation, while light and acid have no impact. The oxidation is fast and complete within one hour for 10% surface coverage at room temperature. In order to study the mechanism and slow down the oxidation, a higher surface coverage of 40% was applied. No unwanted P(V) side products or water adducts were observed. The clean phosphine oxides could be recovered in high yields by washing them off of the AC surface. The oxidation is based on radical activation of O2 on the AC surface due to delocalized electrons on the AC surface. This is corroborated by the result that AIBN-derived radicals enable the air oxidation of PPh3 in solution at 65 °C. When the air-stable complex (CO)2Ni(PPh3)2 is applied to the AC surface and exposed to the air, OPPh3 forms quantitatively. The new surface-assisted air oxidation of phosphines adsorbed on AC renders expensive and hazardous oxidizers obsolete and opens a synthetic pathway to the selective mono-oxidation of bis- and trisphosphines. Full article
(This article belongs to the Section Inorganic Chemistry)
Show Figures

Graphical abstract

18 pages, 5735 KiB  
Article
Fractional Calculus as a Tool for Modeling Electrical Relaxation Phenomena in Polymers
by Flor Y. Rentería-Baltiérrez, Jesús G. Puente-Córdova, Nasser Mohamed-Noriega and Juan Luna-Martínez
Polymers 2025, 17(13), 1726; https://doi.org/10.3390/polym17131726 - 20 Jun 2025
Viewed by 445
Abstract
The dielectric relaxation behavior of polymeric materials is critical to their performance in electronic, insulating, and energy storage applications. This study presents an electrical fractional model (EFM) based on fractional calculus and the complex electric modulus ( [...] Read more.
The dielectric relaxation behavior of polymeric materials is critical to their performance in electronic, insulating, and energy storage applications. This study presents an electrical fractional model (EFM) based on fractional calculus and the complex electric modulus (M*=M+iM) formalism to simultaneously describe two key relaxation phenomena: α-relaxation and interfacial polarization (Maxwell–Wagner–Sillars effect). The model incorporates fractional elements (cap-resistors) into a modified Debye equivalent circuit to capture polymer dynamics and energy dissipation. Fractional differential equations are derived, with fractional orders taking values between 0 and 1; the frequency and temperature responses are analyzed using Fourier transform. Two temperature-dependent behaviors are considered: the Matsuoka model, applied to α-relaxation near the glass transition, and an Arrhenius-type equation, used to describe interfacial polarization associated with thermally activated charge transport. The proposed model is validated using literature data for amorphous polymers, polyetherimide (PEI), polyvinyl chloride (PVC), and polyvinyl butyral (PVB), successfully fitting dielectric spectra and extracting meaningful physical parameters. The results demonstrate that the EFM is a robust and versatile tool for modeling complex dielectric relaxation in polymeric systems, offering improved interpretability over classical integer-order models. This approach enhances understanding of coupled relaxation mechanisms and may support the design of advanced polymer-based materials with tailored dielectric properties. Full article
(This article belongs to the Special Issue Relaxation Phenomena in Polymers)
Show Figures

Figure 1

14 pages, 1252 KiB  
Perspective
Dielectric Spectroscopy: Yesterday, Today and Tomorrow
by Friedrich Kremer and Martin Tress
Appl. Sci. 2025, 15(13), 6954; https://doi.org/10.3390/app15136954 - 20 Jun 2025
Viewed by 285
Abstract
The theory of orientational polarization and dielectric relaxation was developed by P. Debye more than 100 years ago. It approximates a molecule by a sphere having one or more dipole moments. While in the beginning the experimentally accessible spectral range was limited to [...] Read more.
The theory of orientational polarization and dielectric relaxation was developed by P. Debye more than 100 years ago. It approximates a molecule by a sphere having one or more dipole moments. While in the beginning the experimentally accessible spectral range was limited to roughly 6 decades in frequency, at the end of the last century, novel spectroscopic techniques were developed and dielectric spectroscopy became broadband, nowadays covering 18 decades with no gaps.This paved the avenue for a multitude of novel fields of research in soft matter and solid-state physics including fundamental questions like the scaling of relaxation processes or the dynamics of glasses. Yet the analysis of dielectric spectra is still based on the classical approach by Debye which does not consider the multitude of intra- and inter-molecular interactions within a molecular system. To experimentally overcome these principal limitations, it is suggested to take advantage of the molecular specificity of the infrared spectral range. This offers the unique possibility to realize a novel “Orientational Polarization Spectroscopy”, in which the orientational response of a molecular system can be analyzed on an atomistic scale. For that, the theory will be outlined and the first experimental results will be presented. Full article
Show Figures

Figure 1

16 pages, 2150 KiB  
Article
Microwire vs. Micro-Ribbon Magnetoelastic Sensors for Vibration-Based Structural Health Monitoring of Rectangular Concrete Beams
by Christos I. Tapeinos, Dimitris Kouzoudis, Kostantis Varvatsoulis, Manuel Vázquez and Georgios Samourgkanidis
Sensors 2025, 25(12), 3590; https://doi.org/10.3390/s25123590 - 7 Jun 2025
Viewed by 2659
Abstract
Two different magnetoelastic Metglas materials with distinct shapes were compared as sensing elements for the structural health monitoring of concrete beams. One had a ribbon shape, while the other had a microwire shape. The sensing elements were attached to different concrete beams, and [...] Read more.
Two different magnetoelastic Metglas materials with distinct shapes were compared as sensing elements for the structural health monitoring of concrete beams. One had a ribbon shape, while the other had a microwire shape. The sensing elements were attached to different concrete beams, and a crack was introduced into each beam. The beams were subjected to flexural vibrations, and their deformations were recorded wirelessly by coils, detecting the magnetic signals emitted due to the magnetoelastic nature of the sensors. Fast Fourier Analysis of the received signal revealed the bending mode frequencies of the beams, which serve as a “signature” of their structural health. In these spectra, the ribbon-shaped sensor exhibited a 1.4-times stronger signal than the microwire sensor. However, the extracted mode frequencies were nearly identical, with differences of less than 1% both before and after damage. This indicates that both sensors can be used equivalently to monitor structural damage in concrete beams. The damage-related relative frequency shifts ranged from −0.01 to −0.03, with similar results for both sensors. Thermal annealing was also studied and appeared to significantly enhance the signal by 10–30%, likely due to the relaxation of internal stresses induced during the rapid solidification synthesis of these materials. This enhancement was more pronounced in the ribbon-shaped sensor. This study is the first to utilize a magnetoelastic microwire sensor for damage detection in concrete beams. Full article
Show Figures

Graphical abstract

33 pages, 5225 KiB  
Review
A Study of the Dielectric Relaxation of Nitrile–Butadiene Rubber, Ethylene–Propylene–Diene Monomer, and Fluoroelastomer Polymers with a Self-Developed Deconvolution Analysis Program
by Youngil Moon, Gyunghyun Kim and Jaekap Jung
Polymers 2025, 17(11), 1539; https://doi.org/10.3390/polym17111539 - 31 May 2025
Viewed by 1006
Abstract
This study presents an integrated analysis of the dielectric characteristics of nitrile–butadiene rubber (NBR), ethylene–propylene–diene monomer (EPDM), and fluoroelastomer (FKM) polymers. Dispersion spectra were obtained over a wide range of frequencies and temperatures, and, via our self-developed “Dispersion Analysis” program, the obtained dielectric [...] Read more.
This study presents an integrated analysis of the dielectric characteristics of nitrile–butadiene rubber (NBR), ethylene–propylene–diene monomer (EPDM), and fluoroelastomer (FKM) polymers. Dispersion spectra were obtained over a wide range of frequencies and temperatures, and, via our self-developed “Dispersion Analysis” program, the obtained dielectric spectra were precisely deconvoluted. Notably, α, α’, β, and γ relaxation phenomena, including the DC conduction process, were identified in NBR, whereas three relaxation processes, namely, α, β, and the Maxwell‒Wagner‒Sillars (MWS) process, as well as DC conduction, were observed in EPDM and FKM copolymers. The activation energies (Ea) for secondary relaxation—namely, β, γ, and MWS—and the DC conduction process, which are observed in NBR, EPDM, and FKM, were determined via the Arrhenius temperature dependence model, and these values were compared with previously published results. Furthermore, the glass transition temperature (Tg), extrapolated from the relaxation rate of the α process, was estimated via the Vogel–Fulcher–Tamman–Hesse (VFTH) law. The values of Tg obtained using dielectric spectroscopy for NBR, EPDM, and FKM agreed well with the differential scanning calorimetry (DSC) measurements. This study provides foundational insights into the dielectric properties of widely used rubber polymers, offering a comprehensive reference for future research. Full article
(This article belongs to the Section Polymer Physics and Theory)
Show Figures

Figure 1

14 pages, 2524 KiB  
Article
The Effect of the Higher Temperature and UVA Radiation on the Pharmaceutical Preparation Containing Spironolactone—EPR Examination
by Ewa Burek, Barbara Pilawa, Magdalena Zdybel and Ewa Chodurek
Processes 2025, 13(6), 1696; https://doi.org/10.3390/pr13061696 - 28 May 2025
Viewed by 364
Abstract
Electron paramagnetic resonance (EPR) examination of the effect of storage conditions on properties and contents of free radicals formed in the pharmaceutical preparation containing spironolactone, taking into account physical factors such as UVA radiation and the higher temperature, was conducted. The changes in [...] Read more.
Electron paramagnetic resonance (EPR) examination of the effect of storage conditions on properties and contents of free radicals formed in the pharmaceutical preparation containing spironolactone, taking into account physical factors such as UVA radiation and the higher temperature, was conducted. The changes in amplitude (A), integral intensity (I) and EPR linewidth (ΔBpp) of the EPR spectra and free radical contents were determined. It was obtained that free radicals are formed during storage of this preparation under three different treatments: 50 °C, under UVA radiation, and under UVA radiation and a temperature of 50 °C. During storage, the preparation containing spironolactone should be protected from temperatures 50 °C and from UVA radiation. A higher content of free radicals is formed in the tested preparation exposed to both UVA and a temperature of 50 °C, than in the preparation exposed only to UVA or only to a temperature of 50 °C. Similar integral intensities (I) were obtained for the tested preparation exposed to a temperature of 50 °C or exposed to UVA radiation. Fast spin-lattice relaxation processes occur in all tested pharmaceutical preparation samples containing spironolactone. The usefulness of EPR spectral analysis in the study of free radicals formed in pharmaceutical preparations has been confirmed. Full article
Show Figures

Figure 1

20 pages, 3455 KiB  
Article
Pore Structure Characterization of Jurassic Sandstones in the Northeastern Ordos Basin: An Integrated Experimental and Inversion Approach
by Haiyang Yin, Tongjun Chen, Yueyue Li, Haicheng Xu and Wan Li
Minerals 2025, 15(5), 547; https://doi.org/10.3390/min15050547 - 20 May 2025
Viewed by 321
Abstract
Although Mercury Intrusion Porosimetry (MIP) and Nuclear Magnetic Resonance (NMR) are widely used for pore characterization, their effectiveness is fundamentally constrained by theoretical limitations. This study investigated the pore structure characteristics of coal-bearing sandstones from the northeastern Ordos Basin using an integrated approach [...] Read more.
Although Mercury Intrusion Porosimetry (MIP) and Nuclear Magnetic Resonance (NMR) are widely used for pore characterization, their effectiveness is fundamentally constrained by theoretical limitations. This study investigated the pore structure characteristics of coal-bearing sandstones from the northeastern Ordos Basin using an integrated approach combining experimental measurements and model-based inversion. The experimental measurements comprised a stress-dependent acoustic velocity test (P- and S-wave velocities), X-ray diffraction (XRD) mineralogical analysis, and NMR relaxation T2 spectra characterization. For model-based inversion, we developed an improved Mori-Tanaka (M-T) theoretical framework incorporating stress-sensitive pore geometry parameters and dual-porosity (stiff/soft) microstructure representation. Systematic analysis revealed four key findings: (1) excellent agreement between model-inverted and NMR-derived total porosity, with a maximum absolute error of 1.09%; (2) strong correlation between soft porosity and the third peak of T2 relaxation spectra; (3) stiff porosity governed by brittle mineral content (quartz and calcite), while soft porosity showing significant correlation with clay mineral abundance and Poisson’s ratio; and (4) markedly lower elastic moduli (28.78%–51.85%) in Zhiluo Formation sandstone compared to Yan’an Formation equivalents, resulting from differential diagenetic alteration despite comparable depositional settings. The proposed methodology advances conventional NMR analysis by simultaneously quantifying both pore geometry parameters (e.g., aspect ratios) and the stiff-to-soft pore distribution spectra. This established framework provides a robust characterization of the pore architecture in Jurassic sandstones, yielding deeper insights into sandstone pore evolution within the Ordos Basin. These findings provide actionable insights for water hazard mitigation and geological CO2 storage practices. Full article
(This article belongs to the Section Mineral Exploration Methods and Applications)
Show Figures

Figure 1

31 pages, 3727 KiB  
Article
Time-Domain Characterization of Linear Viscoelastic Behavior in Asphalt Mixtures: A Comparative Evaluation Through Discrete and Continuous Spectral Techniques
by Fei Zhang, Bingyuan Huo, Wanmei Gui, Chao Li, Heng Liu, Yongming Xing, Lan Wang and Pucun Bai
Polymers 2025, 17(10), 1299; https://doi.org/10.3390/polym17101299 - 9 May 2025
Viewed by 357
Abstract
This study systematically investigates continuous and discrete spectra methodologies for determining time-domain viscoelastic response functions (creep compliance and relaxation modulus) in asphalt mixtures. Through complex modulus testing of three asphalt mixtures (base asphalt mixture, SBS-modified asphalt mixture, and crumb rubber-modified asphalt mixture), we [...] Read more.
This study systematically investigates continuous and discrete spectra methodologies for determining time-domain viscoelastic response functions (creep compliance and relaxation modulus) in asphalt mixtures. Through complex modulus testing of three asphalt mixtures (base asphalt mixture, SBS-modified asphalt mixture, and crumb rubber-modified asphalt mixture), we established unified master curves using a Generalized Sigmoidal model with approximated Kramers–Kronig (K-K) relations. Discrete spectra can be obtained by Prony series of Maxwell/Kelvin modeling, while continuous spectra derived through integral transformation produced complementary response functions by numerical integration. Comparative analysis demonstrated that discrete and continuous spectra methods yield highly consistent predictions of the relaxation modulus and creep compliance within conventional time scales (10−7–105 s), with significant deviations emerging only at extreme temporal extremities. Compared to discrete spectra results, material parameters (relaxation modulus and creep compliance) derived from continuous spectra methods invariably asymptotically approach upper and lower plateaus. Notably, the maximum equilibrium values derived from continuous spectra methods consistently surpassed those obtained through discrete approaches, whereas the corresponding minimum values were consistently lower. This comparative analysis highlights the inherent limitations in the extrapolation reliability of computational methodologies, particularly regarding spectra method implementation. Furthermore, within the linear viscoelastic range, the crumb rubber-modified asphalt mixtures exhibited superior low-temperature cracking resistance, whereas the SBS-modified asphalt mixtures demonstrated enhanced high-temperature deformation resistance. This systematic comparative study not only establishes a critical theoretical foundation for the precise characterization of asphalt mixture viscoelasticity across practical engineering time scales through optimal spectral method selection, but also provides actionable guidance for region-specific material selection strategies. Full article
(This article belongs to the Special Issue Advances in Functional Rubber and Elastomer Composites, 3rd Edition)
Show Figures

Figure 1

21 pages, 4797 KiB  
Article
Multifractal Characterization of Pore Heterogeneity and Water Distribution in Medium- and High-Rank Coals via Nuclear Magnetic Resonance
by Huan Liu, Shasha Zhang, Yu Qiao, Danfeng Xie and Long Chang
Fractal Fract. 2025, 9(5), 290; https://doi.org/10.3390/fractalfract9050290 - 28 Apr 2025
Viewed by 364
Abstract
Comprehensive assessment of pore structure and multiphase water distribution is critical to the flow and transport process in coalbed methane (CBM) reservoirs. In this study, nuclear magnetic resonance (NMR) and multifractal analysis were integrated to quantify the multiscale heterogeneity of nine medium- and [...] Read more.
Comprehensive assessment of pore structure and multiphase water distribution is critical to the flow and transport process in coalbed methane (CBM) reservoirs. In this study, nuclear magnetic resonance (NMR) and multifractal analysis were integrated to quantify the multiscale heterogeneity of nine medium- and high-rank coals under water-saturated and dry conditions. By applying the box-counting method to transverse relaxation time (T2) spectra, multifractal parameters were derived to characterize pore heterogeneity and residual water distribution. The influencing factors of pore heterogeneity were also discussed. The results show that pore structures in high-rank coals (HCs) exhibit a broader multifractal spectrum and stronger rightward spectrum than those of medium-rank coals, reflecting micropore-dominated heterogeneity and the complexity induced by aromatization in HCs. The vitrinite content enhances micropore development, increasing the heterogeneity and complexity of pore structure and residual water distribution. Inertinite content shows opposite trends compared to vitrinite content for the effect on pore structure and water distribution. Volatile yield reflects coal metamorphism and thermal maturity, which inversely correlates with pore heterogeneity and complexity. Residual water mainly distributes to adsorption pores and pore throats, shortening T2 relaxation (bound water effect) and reducing spectral asymmetry. The equivalence of the multifractal dimension and singularity spectrum validates their joint utility in characterizing pore structure. Minerals enhance pore connectivity but suppress complexity, while moisture and ash contents show negligible impacts. These findings provide a theoretical reference for CBM exploration, especially in optimizing fluid transportation and CBM production strategies and identifying CBM sweet spots. Full article
(This article belongs to the Special Issue Multiscale Fractal Analysis in Unconventional Reservoirs)
Show Figures

Figure 1

25 pages, 8617 KiB  
Article
Structure and Optical Properties of New 2-N-Phenylamino-methyl-nitro-pyridine Isomers
by Patrycja Godlewska, Jerzy Hanuza, Jan Janczak, Radosław Lisiecki, Małgorzata Basiak, Adam Zając and Lucyna Dymińska
Int. J. Mol. Sci. 2025, 26(7), 2874; https://doi.org/10.3390/ijms26072874 - 21 Mar 2025
Viewed by 1231
Abstract
Two new 2-N-phenylamino-(4 or 6)-methyl-3-nitropyridine derivatives were synthesized. Their structures were characterized on the basis of X-ray diffraction, IR, and Raman spectra as well as electron UV-Vis and emission spectra measurements. The experimental results were analyzed in terms of theoretical data [...] Read more.
Two new 2-N-phenylamino-(4 or 6)-methyl-3-nitropyridine derivatives were synthesized. Their structures were characterized on the basis of X-ray diffraction, IR, and Raman spectra as well as electron UV-Vis and emission spectra measurements. The experimental results were analyzed in terms of theoretical data in which the quantum chemical DFT and NBO calculations were applied. To elucidate the relaxation pathways of electronically excited states, multiple excitation wavelengths were employed to probe energy dissipation mechanisms in the studied compounds. A systematic analysis was conducted to evaluate how variations in methyl substituent positioning modulate both the structural architecture and photophysical behavior of the isomeric systems. The spectroscopic, structural and theoretical considerations allow us to propose the potential technological applications derived from the unique properties of these isomers. Full article
(This article belongs to the Section Physical Chemistry and Chemical Physics)
Show Figures

Graphical abstract

12 pages, 3753 KiB  
Article
Unveiling the ESIPT Luminescence Mechanism of 4′-N,N-Diethylamino-3-Hydroxyflavone in Ionic Liquid: A Computational Study
by Jin Yang, Qi Li, Meilin Guo, Lu Yan, Lixia Zhu, Jing Zhao, Guangxiong Hu, Hang Yin and Ying Shi
Molecules 2025, 30(6), 1381; https://doi.org/10.3390/molecules30061381 - 20 Mar 2025
Cited by 1 | Viewed by 493
Abstract
Excited state intramolecular proton transfer (ESIPT) within molecules in solvents plays important roles in photo-chemistry and photo-biology. Herein, the influence of 1-ethyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) imide ([EMIm][NTf2]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) on the ESIPT of 4′-N,N-diethylamino-3-hydroxyflavone (DEAHF) was explored. The [...] Read more.
Excited state intramolecular proton transfer (ESIPT) within molecules in solvents plays important roles in photo-chemistry and photo-biology. Herein, the influence of 1-ethyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) imide ([EMIm][NTf2]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) on the ESIPT of 4′-N,N-diethylamino-3-hydroxyflavone (DEAHF) was explored. The density functional theory and time-dependent density functional theory methodologies were used. The calculated fluorescence spectrum reveals that the fluorescence peaks of DEAHF in [EMIm][NTf2] and [BMIm][PF6] originate from the emission of N* and T* forms. The structure’s optimization, infrared spectra, non-covalent interactions and the scanning of potential energy curves collectively demonstrate that the ESIPT of DEAHF likely happen more in [EMIm][NTf2] than in [BMIm][PF6]. The solvation effects in [BMIm][PF6] exhibit greater prominence compared to those in [EMIm][NTf2], as evidenced by the free energy curve. The alterations in dipole moment indicate a substantial solvation relaxation during the ESIPT processes. Our aforementioned research offers backing for the advancement of novel fluorescent probes. Full article
(This article belongs to the Special Issue Theoretical Study on Luminescent Properties of Organic Materials)
Show Figures

Figure 1

14 pages, 7673 KiB  
Article
Enhanced Luminescence and Thermal Stability in High Gd3+/Eu3+ Co-Doped Ba3Y4O9 Phosphors via Co-Precipitation Method
by Dong Zhu, Chunfeng Wang, Xiaohuai Wang, Shun Han, Yuxiang Zeng, Ming Fang, Wenjun Liu, Deliang Zhu, Peijiang Cao and Youming Lu
Molecules 2025, 30(5), 1085; https://doi.org/10.3390/molecules30051085 - 27 Feb 2025
Cited by 1 | Viewed by 646
Abstract
The co-precipitation method was successfully used to synthesize Ba3(Y0.6−xGd0.4Eux)4O9 (0.01 ≤ x ≤ 0.09) phosphors with heavy Gd3+ doping, resulting in significantly enhanced thermal stability and luminescence performance. Structural analyses confirm [...] Read more.
The co-precipitation method was successfully used to synthesize Ba3(Y0.6−xGd0.4Eux)4O9 (0.01 ≤ x ≤ 0.09) phosphors with heavy Gd3+ doping, resulting in significantly enhanced thermal stability and luminescence performance. Structural analyses confirm that Gd3+ and Eu3+ ions substitute Y3+ in the lattice, causing lattice expansion and improving crystal asymmetry, which enhances Eu3+ emission. The incorporation of Gd3+ creates efficient energy transfer pathways to Eu3+ while suppressing non-radiative relaxation, leading to stable fluorescence lifetimes even at elevated temperatures. With a thermal activation energy of ~0.3051 eV, the Ba3(Y0.55Gd0.4Eu0.05)4O9 phosphor exhibits superior resistance to thermal quenching compared to Ba3(Y0.95Eu0.05)4O9 and many conventional red phosphors. Furthermore, the reduced color temperature and stable emission spectra across a wide temperature range highlight its potential for advanced lighting and display technologies in high-temperature environments. Full article
Show Figures

Graphical abstract

Back to TopTop