arXiv subjects

Marian Paluch

Publications and source records attributed to Marian Paluch.

18 recordsLinked to original sources

arXiv2024

Insight into properties of sizable glass former from volumetric measurements

Sizable glass formers feature numerous unique properties and potential applications, but many questions regarding their glass transition dynamics have not been resolved yet. Here we analyzed structural relaxation times measured as a function of temperature and pressure in combination with the equation of state obtained from pressure-volume-temperature (PVT) measurements. Despite evidence from previous dielectric studies indicating a remarkable sensitivity of supercooled dynamics to compression, and contrary to intuition, our results demonstrated the temperate proof for the almost equivalent importance of thermal energy and free volume fluctuations in controlling reorientation dynamics of sizable molecules. The found scaling exponent equals 3.0 and Ev/Ep ratio of 0.6 were typical for glass-forming materials with relaxation dynamics determined by both effects with a minor advantage of thermal fluctuations involvement. It shows that the high values of key parameters characterizing the sensitivity of the glass transition dynamics to pressure changes, i.e. activation volume and dTg/dP, are not a valid premise for a remarkable contribution of volume on glass transition dynamics.

cond-mat.soft↗

arXiv2024

The breakdown of the direct relation between the density scaling exponent and the intermolecular interaction potential for molecular systems with purely repulsive intermolecular forces

In this work, we question the generally accepted statement that the character of intermolecular interactions can be directly determined from the scaling exponent. Based on detailed studies of polyatomic molecular systems with precisely defined and purely repulsive intermolecular potential, we show that the value of the density scaling exponent evidently differs from the one predicted by the intermolecular virial-potential-energy correlation. Since the latter value directly results from the intermolecular potential, information on the interactions between molecules within the system cannot be immediately gained from the density scaling exponent value. Moreover, we suggest that the recently proposed "molecular force" method also returns the value that varies from the one scaling the dynamics. Finally, basing on our results, it might be deduced that the intramolecular interactions influence the density scaling value for real liquids.

cond-mat.soft↗

arXiv2023

The origin of the density scaling exponent for polyatomic molecules and the estimation of its value from the liquid structure

In this article, we unravel the problem of interpreting the density scaling exponent for the polyatomic molecules representing the real van der Waals liquids. Our studies show that the density scaling exponent is a weighted average of the exponents of the repulsive terms of all interatomic interactions occurring between molecules, wherein the potential energy of a given interaction represents its weight. It implies that potential energy is a key quantity required to calculate the density scaling exponent value for real molecules. Finally, we use the well-known method for potential energy estimation and show that the density scaling exponent could be successfully predicted from the liquid structure for fair representatives of the real systems.

cond-mat.soft↗

arXiv2022

The computational evidence for the crucial role of the dipole cross-correlations in the polar glass-forming liquids

In this letter, we analyze the dipole-dipole correlations obtained from the molecular dynamics simulations for strongly- and weakly-polar model liquids. As a result, we found that cross-correlations contribution to the systems total dipole moment correlation function, which is directly measured in the dielectric spectroscopy experiment, is negligible for weakly-polar liquids. In contrast, the cross-correlations term dominates over the self-correlations one for examined strongly polar-liquid. Consequently, our studies strongly support the interpretation of the dielectric spectra nature of the glass forming liquids, recently proposed by Pabst et al.

cond-mat.soft↗

arXiv2020

Coupling between structural relaxation and diffusion in glass-forming liquids under pressure variation

We theoretically investigate structural relaxation and activated diffusion of glass-forming liquids at different pressures using both the Elastically Collective Nonlinear Langevin Equation (ECNLE) theory and molecular dynamics (MD) simulation. An external pressure restricts local motions of a single molecule within its cage and triggers the slowing down of cooperative mobility. While the ECNLE theory and simulation generally predict a monotonic increase of the glass transition temperature and dynamic fragility with pressure, the simulation indicates a decrease of fragility as pressure above 1000 bar. The structural relaxation time is found to be linearly coupled with the inverse diffusion constant. Remarkably, this coupling is independent of compression. Theoretical calculations agree quantitatively well with simulations and are also consistent with prior works.

cond-mat.soft↗

arXiv2020

Effect of Temperature, Pressure and Aging time on the Relaxation Dynamics of Bi0.9Gd0.1Fe0.9Mn0.1O3 System: Direct Evidence of Glassy State and Pressure Induced Relaxor Behavior

The fundamental aspects of relaxation dynamics in Bi0.9Gd0.1Fe0.9Mn0.1O3 multiferroic system have been reported. The study was carried out employing dielectric relaxation spectroscopy covering eight decades in frequency 0.01 to106 Hz and in a wide range of temperature 423 K to 153 K, hydrostatic pressure 0.1 MPa to 1765 MPa and aging time 0 s to 80000 s. The temperature dependent dielectric response indicates three relaxations processes in the dynamic window of modulus formalism. Variable range hopping model of small polarons manifests the bulk conduction mechanism. The bulk and grain boundary contributions have been estimated using impedance spectroscopy analysis and reveal that localized process dominates the relaxation. The direct evidence of glassy feature is established below 200 K by aging experiments. Our findings provide a potential connection between nearly constant loss features appearing below 200 K with fastest relaxation of magnitude 0.16 eV. We also discuss the time temperature superposition behavior using modulus scaling. A pressure driven normal ferroelectric to relaxor behavior is witnessed above a critical pressure as a result of relative competition between short range and long range forces. Our findings focus the role of high pressure as a fundamental bridge between normal ferroelectrics and relaxors. Intriguingly, there exists a direct connection between chemical pressure induced by substitution and external hydrostatic pressure. These findings have robust fundamental importance on theoretical elucidation of relaxation dynamics in perovskite systems.

cond-mat.mtrl-sci↗

arXiv2020

Theoretical and Experimental Study of Compression Effects on Structural Relaxation of Glass-Forming Liquids

We develop the elastically collective nonlinear Langevin equation theory of bulk relaxation of glass-forming liquids to investigate molecular mobility under compression conditions. The applied pressure restricts more molecular motion and therefore significantly slows-down the molecular dynamics when increasing the pressure. We quantitatively determine the temperature and pressure dependence of the structural relaxation time. To validate our model, dielectric spectroscopy experiments for three rigid and non-polymeric supramolecules are carried out at ambient and elevated pressures. The numerical results quantitatively agree with experimental data.

cond-mat.soft↗

arXiv2020

Molecular relaxations in supercooled liquid and glassy states of amorphous gambogic acid: dielectric spectroscopy, calorimetry and theoretical approach

The relaxation dynamics and thermodynamic properties of supercooled and glassy gambogic acid are investigated using both theory and experiment. We measure the temperature dependence of the relaxation times in three polymorphs (alpha-, beta-, and gamma-form). To gain insight into the relaxation processes, we propose a theoretical approach to quantitatively understand nature of these three relaxations. The alpha-relaxation captures cooperative motions of molecules while the beta-process is mainly governed by local dynamics of a single molecule within the cage formed by its nearest neighbors. Based on quantitative agreement between theory and experimental data, our calculations clearly indicate that the beta-process is a precursor of the structural relaxation and intramolecular motions are responsible for the gamma-relaxation. Moreover, the approach is exploited to study effects of the heating process on alpha relaxation. We find that the heating rate varies logarithmically with Tg and 1000/Tg. These variations are qualitatively consistent with many prior studies.

cond-mat.soft↗

arXiv2019

Effects of Cooling Rate on Structural Relaxation in Amorphous Drugs: Elastically Collective Nonlinear Langevin Equation Theory and Machine Learning Study

Theoretical approaches are formulated to investigate the molecular mobility under various cooling rates of amorphous drugs. We describe the structural relaxation of a tagged molecule as a coupled process of cage-scale dynamics and collective molecular rearrangement beyond the first coordination shell. The coupling between local and non-local dynamics behaves distinctly in different substances. Theoretical calculations for the structural relaxation time, glass transition temperature, and dynamic fragility are carried out over twenty-two amorphous drugs and polymers. Numerical results have a quantitatively good accordance with experimental data and the extracted physical quantities using the Vogel-Fulcher-Tammann fit function and machine learning. The machine learning method reveals the linear relation between the glass transition temperature and the melting point, which is a key factor for pharmaceutical solubility. Our predictive approaches are reliable tools for developing drug formulation.

cond-mat.soft↗

arXiv2019

Theoretical model for the structural relaxation time in co-amorphous drugs

We propose a simple approach to investigate the structural relaxation time and glass transition of amorphous drugs. Amorphous materials are modeled as a set of equal sized hard spheres. The structural relaxation time over many decades in hard sphere fluids is theoretically calculated using the Elastically Collective Nonlinear Langevin Equation theory associated with Kramer's theory. Then, a new thermal mapping from a real material to an effective hard sphere fluid provides temperature-dependent relaxation time, which can compare to experiments. Numerical results quantitatively agree with previous experiments for pharmaceutical binary mixtures having different weight ratios. We carry out experiments to test our calculations for an ezetimibe-simvastatin-Kollidon VA64 mixture. Our approach would provide a simple but comprehensive description of glassy dynamics in amorphous composites.

cond-mat.soft↗

arXiv2018

On the breakdown of the simple Arrhenius law in the normal liquid state

It is common practice to discuss the temperature effect on molecular dynamics of glass formers above the melting temperature in terms of the Arrhenius law. Using dielectric spectroscopy measurements of dc-conductivity and structural relaxation time on the example of the typical glass former propylene carbonate, we provide experimental evidence that this practice is not justified. Our conclusions are supported by employing thermodynamic density scaling and the occurrence of inflection points in isothermal dynamic data measured at elevated pressure. Additionally, we propose a more suitable approach to describe the dynamics both above and below the inflection point based upon a modified MYEGA model.

cond-mat.mtrl-sci↗

arXiv2017

High-pressure cell for simultaneous dielectric and neutron spectroscopy

In this article we report on the design, manufacture and testing of a high-pressure cell for doing simultaneous dielectric and neutron spectroscopy. This cell is a unique tool for studying dynamics on different timescales, from kilo- to picoseconds, covering universal features such as the alpha relaxation and fast vibrations at the same time. The cell, constructed in cylindrical geometry, is made in high-strength aluminum alloy and operates up to 500 MPa in a temperature range between roughly 2 and 320 K. In order to measure the scattered neutron intensity and the sample capacitance simultaneously, a cylindrical capacitor is positioned within the bore of the high-pressure container. The capacitor consists of two concentric electrodes separated by insulating spacers. The performance of this setup has been successfully verified by collecting simultaneous dielectric and neutron spectroscopy data on dipropylene glycol, using both backscattering and time-of-flight instruments. We have carried out the experiments at different combinations of temperature and pressure in both supercooled liquid and glassy state.

physics.ins-det↗

arXiv2017

In search of invariants for viscous liquids in the density scaling regime: Investigations of dynamic and thermodynamic moduli

In this paper, we report on nontrivial results of our investigations of dynamic and thermodynamic moduli in search of invariants for viscous liquids in the density scaling regime by using selected supercooled van der Waals liquids as representative materials. Previously, the dynamic modulus $M_{p-T}$ (defined in the pressure-temperature representation by the ratio of isobaric activation energy and activation volume) as well as the ratio $B_{T}/M_{p-T}$ (where $B_T$ is the thermodynamic modulus defined as the inverse isothermal compressibility) have been suggested as some kind of material constants. We have established that they are not valid in the explored wide range of temperatures $T$ over dozen decades of structural relaxation times $τ$. The temperature dependences of $M_{p-T}$ and $B_T/M_{p-T}$ have been elucidated by comparison with the well-known measure of the relative contribution of temperature and density fluctuations to molecular dynamics near the glass transition, i.e., the ratio of the isochoric and isobaric activation energies, $E^{act}_{V}/E^{act}_{p}$. Then, we have implemented an idea to transform the definition of the dynamic modulus $M_{p-T}$ from the p-T representation to the V-T one. This idea relied on the disentanglement of combined temperature and density fluctuations involved in isobaric parameters has resulted in finding an invariant for viscous liquids in the density scaling regime, which is the ratio of the thermodynamic and dynamic moduli, $B_{T}/M_{V-T}$. In this way, we have constituted a characteristic of thermodynamics and molecular dynamics, which remains unchanged in the supercooled liquid state for a given material, the molecular dynamics of which obeys the power density scaling law.

cond-mat.soft↗

arXiv2015

Adam-Gibbs model in the density scaling regime and its implications for the configurational entropy scaling

To solve a long-standing problem of condensed matter physics with determining a proper description of the thermodynamic evolution of the time scale of molecular dynamics near the glass transition, we extend the well-known Adam-Gibbs model to describe the temperature-volume dependence of structural relaxation times, $τ_α (T,V)$. We employ the thermodynamic scaling idea reflected in the density scaling power law, $τ_α=f(T^{-1} V^{-γ} ) $, recently acknowledged as a valid unifying concept in the glass transition physics, to discriminate between physically relevant and irrelevant attempts at formulating the temperature-volume representations of the Adam-Gibbs model. As a consequence, we determine a straightforward relation between the structural relaxation time $τ_α$ and the configurational entropy $S_c$, giving evidence that also $S_c (T,V)=g(T^{-1} V^{-γ} )$ with the exponent γ that enables to scale $τ_α (T,V)$. This important finding has meaningful implications for the linkage between thermodynamics and molecular dynamics near the glass transition, because it implies that $τ_α$ can be scaled with $S_c$.

cond-mat.soft↗

arXiv2013

Equation of state in the generalized density scaling regime studied from ambient to ultra-high pressure conditions

In this paper, based on the effective intermolecular potential with well separated density and configuration contributions and the definition of the isothermal bulk modulus, we derive two similar equations of state dedicated to describe volumetric data of supercooled liquids studied in the extremely wide pressure range related to the extremely wide density range. Both the equations comply with the generalized density scaling law of molecular dynamics versus $h(ρ) / T$ at different densities $ρ$ and temperatures $T$, where the scaling exponent can be in general only a density function $γ(ρ) = \it{d} \rm{ln} \it{h / d} \rm{ln}ρ$ as recently argued by the theory of isomorphs. We successfully verify these equations of state by using data obtained from molecular dynamics simulations of the Kob-Andersen binary Lennard-Jones liquid. As a very important result, we find that the one-parameter density function $h(ρ)$ analytically formulated in the case of this prototypical model of supercooled liquid, which implies the one-parameter density function $γ(ρ)$, is able to scale the structural relaxation times with the value of this function parameter determined by fitting the volumetric simulation data to the equations of state. We also show that these equations of state properly describe the pressure dependences of the isothermal bulk modulus and the configurational isothermal bulk modulus in the extremely wide pressure range investigated by the computer simulations. Moreover, we discuss the possible forms of the density functions $h(ρ)$ and $γ(ρ)$ for real glass formers, which are suggested to be different from those valid for the model of supercooled liquid based on the Lennard-Jones intermolecular potential.

cond-mat.soft↗

arXiv2013

Dynamic heterogeneity of glass-forming liquids in the density scaling regime

Recent analyses of high pressure measurement data suggest that the degree of the dynamic heterogeneity (χ_4)^max cannot be in general a single variable function of the structural relaxation time τ. For a wide class of real and model supercooled liquids, the molecular dynamics of which obeys a density scaling law at least to a good approximation, we argue that the important relation between the length and time scales that characterize molecular motions near the glass transition is controlled by a density factor. If a power law density scaling is valid for both the structural relaxation times and the degrees of the dynamic heterogeneity we find that the factor is a density power, the exponent of which is a measure of the observed decoupling between τ and (χ_4)^max. Then, the measure can be quantified by a difference between the power law density scaling exponents, which are usually different for τ and (χ_4)^max.

cond-mat.soft↗

arXiv2012

Activation Volume in the Density Scaling Regime: Equation of State and Its Test by Using Experimental and Simulation Data

In this paper, a formalism for the activation volume of glass forming materials is suggested. An isothermal equation of state for the activation volume is formulated, which is extended to a generalized equation of state that describes the activation volume as a function of temperature and pressure. Both the equations of state are very successfully validated by using experimental and simulation data collected for supercooled Kob-Andersen binary Lennard-Jones liquid and materials from various material groups such as van der Waals liquids, polymers, protic ionic liquids, and strongly hydrogen bonded liquids. Some predictions based on these equations of state for the activation volume are also very satisfactorily verified in case of each considered system, especially a kind of the activation volume scaling with the scaling exponent that also constitutes the slope of the expected linear pressure dependence of the isothermal bulk modulus for the activation volume is confirmed. The until recently unexpected negative value of the slope are explained in case of the systems that obey the thermodynamic scaling law at least to a good approximation.

cond-mat.soft↗

arXiv2011

Scaling of Volumetric Data in Model Systems Based on the Lennard-Jones Potential

The crucial problem for better understanding the nature of glass transition and related relaxation phenomena is to find proper interrelations between molecular dynamics and thermodynamics of viscous systems. To gain this aim the recently observed density scaling of viscous liquid dynamics has been very intensively and successfully studied for last years. However, previous attempts at related scaling of volumetric data yielded results inconsistent with those found from the density scaling of molecular dynamics. In this Letter, we show that volumetric data obtained from simulations in simple molecular models based on the Lennard-Jones (LJ) potential, such as Kob-Andersen binary liquids and the Lewis-Wahnström o-terphenyl model, can be scaled by using the same value of the exponent, which scales dynamic quantities and is directly related to the exponent of the repulsive inverse power law that underlies short-range approximations of the LJ potential.

cond-mat.soft↗