Jul 2026· Physical Chemistry, Chemical Physics - PCCP· Vol 28, pp. 18366-18380· 0 citations· 39 references
Medicine
Abstract
The dynamic behaviour of quadrol (N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine) in its glassy and supercooled liquid states is examined through a combined experimental and computational approach. Owing to its strong hydrogen-bonding capability and stereochemical complexity, quadrol avoids crystallization and exhibits a glass transition close to -30 °C. Dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC) have been employed to probe the α-relaxation, secondary relaxation modes and physical aging phenomena. The α-relaxation shows a marked non-Arrhenius temperature dependence and dominates the dielectric response, either in DRS and TSDC results; additionally, calorimetric and TSDC measurements reveal a strong sensitivity to thermal history and aging conditions. Below Tg, two secondary relaxations become clearly discernible. The faster γ-relaxation, which appears at lowest temperatures, exhibits kinetic features characteristic of localized molecular motions. By contrast, the slower β-relaxation shows a pronounced sensitivity to both aging and water content, signaling a more complex underlying mechanism. The dc electrical conductivity follows a VFTH-like temperature dependence and displays a partially decoupled from the α relaxation. Complementary molecular simulations provide atomistic insight into conformational preferences and hydrogen-bonding environments, offering a microscopic basis for the observed relaxation behaviour. Taken together, these results reinforce the value of quadrol as a model system for probing the interplay between molecular mobility, hydrogen bonding, and dynamic arrest in amorphous organic materials.
To elucidate the relationship between physical aging and molecular dynamics in poly(4-alkylstyrene), three types of measurements were performed: capacitive dilatometry (CD), differential scanning calorimetry (DSC), and dielectric relaxation spectroscopy (DRS). Using CD and DSC, we successfully observed volume and enthalpy relaxation processes during isothermal aging in the glassy state. DRS measurements revealed four dynamical processes: the α-process, β-process, γ-process, and a slower process, in addition to the contribution from DC conductivity. The relaxation times of volume and enthalpy relaxation processes below the glass transition temperature, Tg, were well described by the Arrhenius law, and their activation energies were nearly identical to that of the slower process. This suggests that the microscopic origin of the kinetics of the volume and enthalpy relaxation processes below Tg may be the same as that of the slower process observed above Tg. Near Tg, the relaxation times for volume and enthalpy relaxations deviate from the Arrhenius law and follow the Vogel-Fulcher-Tammann law for the α-process. The α-process appears to govern physical aging near Tg.
Koji Fukao, Akira Goda, Airi Kawano et al.· Journal of Chemical Physics· 0 citations
We report a comparative picosecond dielectric relaxation study of trihydric alcohols (glycerol, 1,2,4-butanetriol, 1,2,5-pentanetriol, 1,2,6-hexanetriol) in binary mixtures with dimethyl sulfoxide (DMSO). Using time-domain reflectometry (TDR) in the GHz frequency range of 10 MHz to 30 GHz, we determined ε₀, τ, geff, Bruggeman factor, and excess parameters. The relaxation dynamics showed pronounced dependence on chain length and hydroxyl arrangement: longer chain triols exhibited deviations from ideal mixing due to enhanced flexibility, whereas glycerol retained unique relaxation due to compact hydrogen-bonding networks. Excess parameters and Kirkwood factors confirmed cooperative/anti-cooperative dipolar behavior modulated by solute structure. These results fill a gap in dielectric relaxation literature on trihydric alcohols and provide insights for solvent system design in biochemical and cryoprotective applications.
Pramod R. Konmare, A. Bokhare, N. Garad et al.· Spectrochimica Acta Part A -...· 0 citations
In this work, the dynamics and viscoelasticity of styrene butadiene rubber (SBR) are systematically explored for different temperatures (T) and pressures (P), where the coarse-grained model and potential functions are developed by the iterative Boltzmann inversion approach. The simulation results reveal that the dynamics at the monomer and chain scales display different dependencies on T and P. Thus, a time-T-P superposition principle (TTPSP) holds at both the monomer and chain scales for the translational dynamics. However, TTPSP fails at the monomer scale for the relaxation dynamics while remaining valid at the chain scale at a high T. Meanwhile, a low T enhances dynamical heterogeneity, while a high P reduces fragility, which also reduces the monomer mobility. The universal correlations among the relaxation time, corresponding peak height, Debye-Waller factor, T, and P are derived. These indicate the reduced anisotropy of cage shapes at a high P value and some decoupling or coupled relationships. Finally, the storage modulus, loss modulus, and viscosity of SBR are analyzed, which exhibit a gradual increase with decreasing T or increasing P. Interestingly, the viscoelastic properties present a strong relationship with local chain stiffness. TTPSP holds for viscoelasticity at a high T, while it breaks down over the entire T range, which mainly originates from the complex multiscale dynamical behavior of SBR. In summary, this work provides a comprehensive understanding of how temperature and pressure influence the dynamics and viscoelasticity of the SBR.
Yang Zhang, Xiangbao Wang, Ruibin Ma et al.· Langmuir· 0 citations
Chemical short-range order (CSRO), the non-random local arrangement of atoms in solid solutions, strongly affects the phase stability and performance of medium- and high-entropy alloys (M/HEAs). Despite its importance, the fundamental nature of CSRO formation remains contested: is it a formal thermodynamic transition? Here, investigating CoCrNi as a model system, we indicate that the main CSRO transformations observed in alloys might not be classical thermodynamic transitions, but instead a kinetic arrest phenomenon analogous to the glass transition. Combining atomistic simulations and in situ synchrotron dilatometry experiments enabled the study of CSRO evolution and its structural impact across multiple length scales. For example, CSRO-driven changes in bond lengths and bond distribution significantly impact the observed lattice parameter and volume, allowing Warren-Cowley parameter values to be determined over a full experimental temperature range. We demonstrate that the degree of CSRO and the apparent transition temperatures, defined here as the komplex reaction temperatures (Tkr), are not intrinsic material constants. Rather, they are path-dependent quantities governed by thermal history and diffusional constraints, directly reflecting the frozen CSRO state. Our findings clarify the thermodynamic and kinetic mechanisms underlying CSRO evolution and establish a framework to distinguish thermodynamic transitions under kinetic constraints from genuine kinetically arrested phenomena. Understanding this distinction is crucial for controlling CSRO during alloy design and processing and provides a foundation for future investigations exploring the implications of CSRO in advanced materials. In situ synchrotron dilatometry and atomistic simulations indicate that changes between chemical short-range order states (evolving local chemical distributions) are governed by a kinetic arrest phenomenon rather than a thermodynamic transition.
G. C. Stumpf, Yifan Cao, V. Bacurau et al.· Nature Communications· 0 citations
We combine dielectric and viscoelastic measurements with novel statistical mechanical theories to establish and understand strong decoupling of cation activated dynamics from the polymer segmental relaxation in polymerized ionic liquids. Weakly ion-dependent (Li, Na, K) apparent power laws with fractional exponents between the two characteristic time scales (ionic and segmental) are observed and predicted in the supercooled regime. The ratio of segmental to ion relaxation times grows in a strongly non-Arrhenius manner with cooling. However, at high (fast) enough temperature (segmental relaxation), the theory predicts that decoupling continuously vanishes, and a linear Walden-like proportionality between the two relaxation times is recovered. The theoretical analysis spans 20 decades in time, including the glass state. The mechanistic key to the rich dynamics is the extent to which ion-activated barrier crossing is coupled with in-cage local polymer dynamical fluctuations that facilitate ion hopping.
Ankita Das, H. Singh, Shi-Nian Cheng et al.· ACS Macro Letters· 0 citations
Supercritical water (SCW) exhibits anomalous thermophysical properties that are notoriously challenging to reproduce computationally due to the progressive disruption of the hydrogen-bond network and the interplay between many-body interactions, density fluctuations, and thermal disorder. Here, we demonstrate that the data-driven many-body MB-pol(2023) potential quantitatively reproduces the liquid-to-supercritical crossover of water with near-experimental accuracy over temperatures between 400 and 900 K and pressures from 25 to 100 MPa. Molecular dynamics simulations show that MB-pol(2023) accurately captures the temperature evolution of density and reproduces the anomalous behavior of the isothermal compressibility, thermal expansivity, and heat capacity near the critical region. Along the 25 MPa isobar, these response functions exhibit pronounced maxima between 650 and 670 K, yielding a pseudo-critical Widom-line temperature of TWL ≈ 660 ± 4 K, in excellent agreement with experimental estimates from NIST and IAPWS data (i.e., 660 K). Structural analysis reveals a continuous collapse of tetrahedral order and hydrogen-bond connectivity across the crossover, accompanied by the disappearance of medium-range correlations in radial distribution functions. The hydrogen-bond network evolution correlates almost universally with density, independently of pressure, supporting the interpretation of SCW as a density-driven fluid. Dynamical observables further reveal a sharp increase in molecular mobility near the Widom line. Complementary ab initio molecular dynamics simulations at 900 K and 25 MPa show no evidence of water dissociation and confirm the reliability of the non-reactive MB-pol(2023) model under these extreme conditions. Although trained exclusively on accurate quantum-mechanical data without explicit thermodynamic information, MB-pol(2023) emerges as a quantitatively reliable framework for describing water across the liquid-to-supercritical continuum.
Gaetano Denaro, G. Cassone· Journal of Chemical Physics· 0 citations
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