Inhomogeneous Dynamics Research Articles

Self‐Consistent Thermodynamics and Dynamics during Polymer Glass Transitions

AbstractThe mechanisms behind the polymer glass transition, though not fully elucidated, have garnered significant attention. The Locally Correlated Lattice (LCL) theory [R. P. White, J. E. Lipson, Macromolecules 2016, 49, 3987] provides a novel perspective on free volume and establishes the relationship between polymer glass transition and free volume. In this study, we present a dynamic theoretical model based on the thermodynamic LCL theory, focusing on the kinetic evolution of free volume during polymer glass transition. Our analysis simultaneously examines the segmental diffusion coefficient, dynamic correlation length, free volume, and isobaric heat capacity. The results indicate that, upon reaching a critical temperature, heterogeneous dynamics and singular thermodynamics emerge concurrently. This study establishes a comprehensive correlation between thermodynamic singularities and dynamic inhomogeneities, offering valuable insights into the polymer glass transition process.

In-layer inhomogeneity of molecular dynamics in quasi-liquid layers of ice

Quasi-liquid layers (QLLs) are present on the surface of ice and play a significant role in its distinctive chemical and physical properties. These layers exhibit considerable heterogeneity across different scales ranging from nanometers to millimeters. Although the formation of partially ice-like structures has been proposed, the molecular-level understanding of this heterogeneity remains unclear. Here, we examined the heterogeneity of molecular dynamics on QLLs based on molecular dynamics simulations and machine learning analysis of the simulation data. We demonstrated that the molecular dynamics of QLLs do not comprise a mixture of solid- and liquid water molecules. Rather, molecules having similar behaviors form dynamical domains that are associated with the dynamical heterogeneity of supercooled water. Nonetheless, molecules in the domains frequently switch their dynamical state. Furthermore, while there is no observable characteristic domain size, the long-range ordering strongly depends on the temperature and crystal face. Instead of a mixture of static solid- and liquid-like regions, our results indicate the presence of heterogeneous molecular dynamics in QLLs, which offers molecular-level insights into the surface properties of ice.

Topologically Engineered Strain Redistribution in Elastomeric Substrates for Dually Tunable Anisotropic Plasmomechanical Responses.

The prompt visual response is considered to be a highly intuitive tenet among sensors. Therefore, plasmomechanical strain sensors, which exhibit dynamic structural color changes, have recently been developed by using mechanical stimulus-based elastomeric substrates for wearable sensors. However, the reported plasmomechanical strain sensors either lack directional sensitivity or require complex signal processing and device design strategies to ensure anisotropic optical responses. To the best of our knowledge, there have been no reports on utilizing anisotropic mechanical substrates to obtain directional optical responses. Herein, we propose an anisotropic plasmomechanical sensor to distinguish between the applied force direction and the force magnitude. We employ a simple strain-engineered topological elastomer to mechanically transform closely packed metallic nanoparticles (NPs) into anisotropic directional rearrangements depending on the applied force direction. The proposed structure consists of a heterogeneous-modulus elastomer that exhibits a highly direction-dependent Poisson effect owing to the periodically line-patterned local strain redistribution occurring due to the same magnitude of applied external force. Consequently, the reorientation of the self-assembled gold (Au)-NP array manifests dual anisotropy, i.e., force- and polarization-direction-dependent plasmonic coupling. The cost-effectiveness and simple design of our proposed heterogeneous-modulus platform pave the way for numerous optical applications based on dynamic transformation and topological inhomogeneities.

Structure and Dynamic Inhomogeneity of Liquids on the Liquid–Gas Coexistence Curve Near the Triple Point

Structure and Dynamic Inhomogeneity of Liquids on the Liquid–Gas Coexistence Curve Near the Triple Point

Post-acquisition correction of NMR spectra distorted by dynamic and static field inhomogeneity of cryogen-free magnets

Post-acquisition correction of NMR spectra is an important part of NMR spectroscopy that enables refined NMR spectra to be obtained, clean from undesirable out-phasing, broadening and noising. We describe analytical and numerical mathematical methods for post-acquisition correction of NMR spectra distorted by static and dynamic magnetic field inhomogeneity caused by imperfections of main superconducting coils and the cold head operation, typical for cryogen-free magnets. For the dynamic inhomogeneity, we apply a variant of the general reference deconvolution method, complemented with our mathematical analysis of spectral parameters. For the static inhomogeneity, we apply the method of a delayed Fourier transform, also supported with our analytical calculations. We verify our approach by correction processing of high-field experimental liquid-state 1H NMR spectra of water and ethanol as well as solid-state 13C MAS NMR spectra of adamantane and obtain good results for both static and dynamic field distortions. This work complements our previous work on instrumental suppression of dynamic distortions caused by the cold head operation. The results presented contribute well to the general field of processing NMR spectra and serve towards a more extensive use of cryogen-free magnets in high-resolution NMR spectroscopy.

Nanoscale inhomogeneity of charge density waves dynamics in La2−xSrxNiO4

While stripe phases with broken rotational symmetry of charge density are known to emerge in doped strongly correlated perovskites, the dynamics and heterogeneity of spatial ordering remain elusive. Here we shed light on the temperature dependent lattice motion and the spatial nanoscale phase separation of charge density wave order in the archetypal striped phase in La2−xSrxNiO4+y (LSNO) perovskite using X-ray photon correlation spectroscopy (XPCS) joint with scanning micro X-ray diffraction (SµXRD). While it is known that the CDW in 1/8 doped cuprates shows a remarkable stability we report the CDW motion dynamics by XPCS in nickelates with an anomalous quantum glass regime at low temperature, T < 65 K, and the expected thermal melting at higher temperature 65 < T < 120 K. The nanoscale CDW puddles with a shorter correlation length are more mobile than CDW puddles with a longer correlation length. The direct imaging of nanoscale spatial inhomogeneity of CDW by scanning micro X-ray diffraction (SµXRD) shows a nanoscale landscape of percolating short range dynamic CDW puddles competing with large quasi-static CDW puddles giving rise to a novel form of nanoscale phase separation of the incommensurate stripes order landscape.

Dynamic Investigation of Battery Materials via Advanced Visualization: From Particle, Electrode to Cell Level.

Li-ion batteries, the most-popular secondary battery, are typically electrochemical systems controlled by ion-insertion dynamics. The battery dynamics involve mass transport, charge transfer, ion-electron coupled reactions, electrolyte penetration, ion solvation, and interfacial evolution. However, it is difficult for the traditional electrochemical methods to capture the accurate and individual details of the dynamic processes in "black box" batteries; instead, only the net result of multi-factors on the whole scale. Recently, different advanced visualization techniques have been developed, which provide powerful tools to track and monitor the internal real-time dynamic processes, giving intuitive details and fine information at various scales from crystal lattice, single particle, electrode to cell level. Here, the recent progress on the investigation of electrochemical dynamics in battery materials are reviewed, via developed techniques across wide timescales and space-scales, including the dynamic process inside the active particle, kinetics issues at the electrode/electrolyte interface, dynamic inhomogeneity in the electrode, and dynamic transportation at the cell level. Finally, the fundamental principles to improve the battery dynamics are summarized and new technologies for future more stringent conditions are highlighted. In prospect, this review opens sight on the battery interior for a clearer, deeper, and more thorough understanding of the dynamics.

Influence of dynamic inhomogeneity of the stress-strain state on the modes of wire drawing in a monolithic conical die

The study of the wire drawing speed influence in a monolithic conical die on the stressstrain state inhomogeneity and drawing modes was presented. It was shown that the nonuniformity of stresses and strains during drawing in monolithic round dies could be divided into two types: static and dynamic. When drawing a round wire in a monolithic conical die, stress-strain state inhomogeneity occurs in the deformation zone, which results in microcracks at the wire center. The destruction degree depends on the value of &Delta;-factor, which characterizes the shape of the deformation zone. When the drawing speed increases, an additional speed or dynamic deformation inhomogeneity arises in the deformation zone due to the resulting acceleration and an increase in stresses. This causes a significant increase in the parameter &Delta; and the working half-angle of die, called &ldquo;dynamic&rdquo;. Analytical expressions were obtained for calculating the &ldquo;dynamic&rdquo; die angle and its velocity part. The analytical expressions analysis was carried out, the relationships between parameter &Delta; and the die half-angle on the drawing speed were obtained. A graphical dependence of the change in the safe zone, which excludes the destruction of the wire, on the value of the &ldquo;dynamic&rdquo; die angle and the degree of single deformation at various drawing speeds was plotted. It was shown that the &ldquo;safe&rdquo; zone decreases in proportion to the increase in the drawing speed. Solutions were proposed that provide an &ldquo;acceptable&rdquo; value of the parameter &Delta; for high-speed drawing. For this necessary to design wire drawing schedules using the maximum possible reductions per pass, and the values of the working half-angles of the wire drawing die, providing &ldquo;static&rdquo; inhomogeneity, should be reduced by the value of half-angles dynamic change. Wire drawing should be carried out at minimum tensile stresses.

Possible quadrupole-order-driven commensurate-incommensurate phase transition in B20 CoGe

The B20-type cobalt germanide CoGe was investigated by measuring the specific heat, resistivity, and $^{59}$Co nuclear magnetic resonance (NMR). We observed a phase transition at $T_Q=13.7$ K, evidenced by a very narrow peak of the specific heat and sharp changes of the nuclear spin-spin ($T_2^{-1}$) and spin-lattice ($T_1^{-1}$) relaxation rates. The fact that the entropy release is extremely small and the Knight shift is almost independent of temperature down to low temperatures as anticipated in a paramagnetic metal indicates that the $T_Q$ transition is of non-magnetic origin. In addition, we detected a crossover scale $T_0\sim30$ K below which the resistivity and the NMR linewidth increase, and $T_1^{-1}$ is progressively distributed in space, that is, a static and dynamical spatial inhomogeneity develops. While the order parameter for the $T_Q$ transition remains an open question, a group-theoretical analysis suggests that the finite electric quadrupole density arising from the low local site symmetry at cobalt sites could drive the crystal symmetry lowering from the P2$_1$3 symmetry that is commensurate to the R3 symmetry with an incommensurate wavevector, which fairly well accounts for the $T_Q$ transition. The quadrupole-order-driven commensurate-incommensurate phase transition may be another remarkable phenomenon arising from the structural chirality inherent in the noncentrosymmetric B20 family.

Effect of Viscosity Action and Capillarity on Pore-Scale Oil–Water Flowing Behaviors in a Low-Permeability Sandstone Waterflood

Water flooding technology is an important measure to enhance oil recovery in oilfields. Understanding the pore-scale flow mechanism in the water flooding process is of great significance for the optimization of water flooding development schemes. Viscous action and capillarity are crucial factors in the determination of the oil recovery rate of water flooding. In this paper, a direct numerical simulation (DNS) method based on a Navier–Stokes equation and a volume of fluid (VOF) method is employed to investigate the dynamic behavior of the oil–water flow in the pore structure of a low-permeability sandstone reservoir in depth, and the influencing mechanism of viscous action and capillarity on the oil–water flow is explored. The results show that the inhomogeneity variation of viscous action resulted from the viscosity difference of oil and water, and the complex pore-scale oil–water two-phase flow dynamic behaviors exhibited by capillarity play a decisive role in determining the spatial sweep region and the final oil recovery rate. The larger the viscosity ratio is, the stronger the dynamic inhomogeneity will be as the displacement process proceeds, and the greater the difference in distribution of the volumetric flow rate in different channels, which will lead to the formation of a growing viscous fingering phenomenon, thus lowering the oil recovery rate. Under the same viscosity ratio, the absolute viscosity of the oil and water will also have an essential impact on the oil recovery rate by adjusting the relative importance between viscous action and capillarity. Capillarity is the direct cause of the rapid change of the flow velocity, the flow path diversion, and the formation of residual oil in the pore space. Furthermore, influenced by the wettability of the channel and the pore structure’s characteristics, the pore-scale behaviors of capillary force—including the capillary barrier induced by the abrupt change of pore channel positions, the inhibiting effect of capillary imbibition on the flow of parallel channels, and the blockage effect induced by the newly formed oil–water interface—play a vital role in determining the pore-scale oil–water flow dynamics, and influence the final oil recovery rate of the water flooding.

Origin of Kinetic Dispersion in Eosin-Sensitized TiO2: Insights from Single-Molecule Spectroscopy

By removing the effects of ensemble averaging and molecular aggregation, we untangle the factors that govern the dispersive electron transfer kinetics of eosin-sensitized TiO2, focusing on the impact of environmental heterogeneity versus injection from multiple excited states. The blinking dynamics of single eosin Y chromophores on nanocrystalline TiO2 films are analyzed using a change point detection algorithm for binned data. Robust statistical analysis based on maximum likelihood estimation, Kolmogorov–Smirnov tests, and log likelihood ratio tests is used to determine the functional form that best fits the resulting on- and off-time distributions and to distinguish between mechanisms for dispersive electron transfer. Using this approach, we find that the on- and off-time distributions for eosin Y on TiO2 are best fit to lognormal distributions corresponding to μon = −0.64 ± 0.04, σon = 1.52 ± 0.02, μoff = −0.23 ± 0.04, and σoff = 1.96 ± 0.03, respectively. Monte Carlo simulations based on the Albery model for dispersive electron transfer (i.e., where the median rate constant κ is modified by the exponential of a parameter, x, that is normally distributed, k = κ e–γx) successfully reproduce this behavior using a median rate constant for injection and back electron transfer of ∼1010 and ∼104 s–1, respectively, and a corresponding energetic dispersion, γ, of ∼200–350 meV. To examine how injection from both the singlet and triplet excited states contributes to this dispersion, we studied two rhodamine sensitizers, R123 and 5ROX, that inject only from their singlet excited state. Surprisingly, when access to the T1 state is minimized in going from EY to R123 and 5ROX, kinetic dispersion actually increases. Collectively, these observations support the interpretation that static and dynamic inhomogeneities at the EY–TiO2 interface govern kinetic dispersion, with dynamic fluctuations in binding configuration and/or vibrational motion playing a decisive role.

Influence of spatial static and dynamic inhomogeneities on the distribution of electroelastic fields and electronic processes in piezoceramic composites

The electroelasticity problems for piezoceramic bodies with inhomogeneities were examined. The short review of model situations considered in the previous works of the authors, a piezoceramic body with an internal elliptical crack, a piezoceramic body containing an external elliptical crack, a piezoceramic body with a spherical cavity, was carried out. In all these cases, the coupled electroelastic field in the neighborhood of inhomogeneity for the particular case of static loading was investigated. The formulas to calculate the stress intensity factors were analyzed. The dependences of stresses and electric displacement on the shape of the cavity for the cases of electrical loading and the mechanical loading only were examined. The possibility to apply the obtained results to solving of practical problems, not only static but also dynamic nature, was considered.

Reorientation motions of N-acetyl-tryptophan-amide (NATA dipeptide) in aqueous solution and with co-solvents: Molecular dynamics vs hydrodynamic model

We present a study of peptide reorientational dynamics in solution analyzed from the perspective of fluorescence anisotropy decay (FAD) experiments, and atomistic molecular dynamics (MD) and continuum hydrodynamics modeling. Earlier, FAD measurements and MD simulations of the model dipeptide N-acetyltryptophanamide (NATA) in explicit water and in aqueous solutions of urea, guanidinium chloride, and proline co-solvents identified excellent agreement of MD results with experimental data, indicating the presence of significant effects of peptide–solvent interactions, and the overall tumbling of the peptide could be well described by contributions from individual conformers, represented by dihedral-restrained MD. Here, we extend these studies by analyzing dynamic inhomogeneity in the solutions and by developing a hydrodynamic model (HM) of the conformer dynamics. The MD simulation data indicate the presence of markedly different dynamic microenvironments for the four studied solutions, with the average water reorientations being different in all systems, partly reflecting the bulk viscosities. Additionally, the water dynamics also exhibited a marked slowdown in the vicinity of the co-solvents, especially chloride and proline. To gain further insight, we applied the HM to predict rotational correlation times of tryptophan for the individual NATA conformers identified in MD. The hydrodynamic results were in very good agreement with MD simulations for the individual structures, showing that the HM model provides a realistic description of rotational diffusion for rigid peptide structures. Overall, our study generated new microscopic insights into the complex nature of the structure and dynamics of peptide solvation shells for systems containing water and denaturing and stabilizing co-solvents.

Effect of minor addition on dynamic mechanical relaxation in ZrCu-based metallic glasses

The dynamic mechanical behavior of Zr50-xCu34Ag8Al8Pdx (x = 0 and 2) bulk metallic glasses was probed by mechanical spectroscopy. The results suggest that microalloying retards the relaxation dynamics. The physical aging was analyzed considering a model based on the variation of the concentration of flow units and the Kohlrausch-Williams-Watts (KWW) equation. In the current study, the characteristic parameters of the two models, βc and βaging, reflect the faster annihilation of flow units at higher temperature and the increase of dynamic heterogeneity with temperature, respectively. The mechanical relaxation spectrum was also analyzed. Based on the KWW equation and the quasi-point defect model, replacing Zr with a small amount of Pd can slightly increase the dynamic inhomogeneity and reduce the defect concentration. The analysis according to the HN function suggests that the addition of Pd increases the relaxation time. However, it does not significantly alter the shape of the relaxation time distribution.

Impurity moments conceal low-energy relaxation of quantum spin liquids

We scrutinize the magnetic properties of $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl through its first-order metal-insulator transition at $T_{\rm CO}=30$ K by means of $^1$H nuclear magnetic resonance (NMR). While in the metal we find Fermi-liquid behavior with temperature-independent $(T_1T)^{-1}$, the relaxation rate exhibits a pronounced enhancement when charge order sets in. The NMR spectra remain unchanged through the transition and no magnetic order stabilizes down to 25 mK. Similar to the isostructural spin-liquid candidates $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ and $\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$, $T_1^{-1}$ acquires a dominant maximum (here around 5 K). Field-dependent experiments identify the low-temperature feature as a dynamic inhomogeneity contribution that is typically dominant over the intrinsic relaxation but gets suppressed with magnetic field.

Structure, Dynamics, and Some Properties of Water

Development of ideas of liquid water structure since the end of the 19th century is briefly reviewed. According to the modern concepts based on experimental data and computer simulation, there is a three-dimensional hydrogen bond network in water. The structural and dynamic inhomogeneity of this network is analyzed in detail.

Effect of Wire-Drawing Process Conditions on Secondary Recrystallization Behavior During Annealing in High-Purity Copper Wires

The relationship between the process condition of wire-drawing and the microstructural evolution during the subsequent annealing was investigated for the production of high-purity copper wires. Three wire-drawing process conditions were considered according to the reduction in the area per pass and the die angle, and their effects on the evolution of the grain structure and texture during annealing were investigated. Strain distributions, calculated using the finite element method, showed that the shear strain near the wire surface varies according to the process condition. The electron backscatter diffraction results indicate that the location on the cross-section of the wire, where secondary recrystallization initiates during annealing, is closely related to the shear strain during wire-drawing. Meanwhile, the effect of shear deformation on the grain structure and texture after primary recrystallization is insignificant. Drawing process conditions with a small reduction in the area per pass and die angle resulted in a relatively small shear strain and gave rise to the onset of secondary recrystallization at the central region of the wires. In contrast, the condition with a large reduction in the area per pass and die angle led to a high shear strain and the onset of secondary recrystallization at the peripheral region of the wire. The observed primary and secondary recrystallization behavior during annealing was explained from the viewpoint of dynamic material phenomena and inhomogeneity in the local recrystallization texture, regulated by the extent of shear deformation during wire-drawing.

Localized waves at a line of dynamic inhomogeneities: General considerations and some specific problems

We consider a body, homogeneous or periodic, equipped with a structure composed of dynamic inhomogeneities uniformly distributed along a line, and study free and forced sinusoidal waves (Floquet - Bloch waves for the discrete system) in such a system. With no assumption concerning the wave nature, we show that if the structure reduces the phase velocity, the wave localizes exponentially at the structure line, and the latter can expand the transmission range in the region of long waves. Based on a general solution presented in terms of non-specified Green’s functions, we consider the wave localization in some continuous elastic bodies and a regular lattice. We determine the localization-related frequency ranges and the localization degree in dependence on the frequency. While 2D-models are considered throughout the text, the axisymmetric localization phenomenon in the 3D-space is also mentioned. The dynamic field created in such a structured system by an external harmonic force is obtained consisting of three different parts: the localized wave, a diverging wave, and non-spreading oscillations. Expressions for the wave amplitudes and the energy fluxes in the waves are presented.

Decoupling from a Thermal Bath via Molecular Polariton Formation.

The coupling between an electronic system and an environmental bath plays a decisive role in the excited state dynamics of artificial/natural molecular condensed phases. Although it is generally difficult to control the coupling between the system and the thermal bath in condensed matter, a strong light-matter coupling can control system-bath coupling properties using the polaron decoupling effect, in which a coherent interaction between excitons and photons reduces the reorganization energy. Here we demonstrate that this polaron decoupling strongly reduces the fluctuations in electronic energy in tetraphenyldibenzoperiflanthene thin films embedded in an optical microcavity. Using two-dimensional electronic spectroscopy, the frequency-fluctuation correlation function of the lower polariton state was revealed, showing that the dynamic inhomogeneity due to bath coupling inside the microcavity almost vanishes completely. This was attributed to a significant delocalization of the lower polariton state over 105 molecules in the cavity, reducing the effective coupling strength of the bath modes.

Dual-Modality Confocal Laser Feedback Tomography for Highly Scattering Medium

The combination of optical modalities is a common practice to improve the efficiency of biomedical optics systems. We propose confocal laser feedback tomography for volumetric dual-modality imaging. Two major modalities of laser Doppler flowmetry and reflectance confocal microscopy were integrated, and the signals were concurrently acquired for cross-sectional and volumetric imaging, by means of a compact laser scanning system. The technique was applied to a two-layered skin tissue phantom containing a 200- $\mu \text{m}$ -diameter intralipid flow channel that features functional and morphological changes at the same time. Results show the potential for concurrent 3-D mapping of dynamic and static inhomogeneities in a highly scattering medium which can improve the contrast in non-invasive biological tissue imaging, providing a confocal image in addition to the Doppler flowmetry image.