Van Der Waals Liquid Research Articles

Experimental examination of dipole-dipole cross-correlations by dielectric spectroscopy, depolarized dynamic light scattering, and computer simulations of molecular dynamics.

The contribution of cross- and self-correlations to the dielectric and light-scattering spectra of supercooled polar glass formers has recently become a most challenging problem. Herein, we employ dielectric spectroscopy, depolarized dynamic light scattering (DDLS), and rheology to thoroughly examine the dynamics of van der Waals liquid 1,2-Diphenylvinylene. Carbonate (DVC), which is a polar counterpart of canonical glass former ortho-Terphenyl (OTP). We show that the light-scattering data correspond well with the dielectric permittivity function over a wide T range. This pattern is very different from the peaks' separation ω_{max}^{DDLS}/ω_{max}^{BDS}=3.7 reported recently for tributyl phosphate (TBP), despite the same dielectric characteristics of these two glass formers (β_{KWW}=0.75,Δɛ=20 for both TBP and DVC; KWW stands for Kohlrausch-Williams-Watts). This indicates different influence of orientational correlations in both methods for these two systems. We also show the results of the computer simulations of the model, polar molecules, which clearly indicate that the contribution of the cross-term to the correlation function probed in the DDLS experiment can be significant.

Einstein–AdS gravity coupled to modified arctan-electrodynamics, magnetic black hole thermodynamics and Joule–Thomson expansion

The metric and mass functions of Einstein–AdS gravity coupled to modified arctan- electrodynamics (proposed here) are obtained. We find corrections to the Reissner–Nordström solution. It is demonstrated that if the Schwarzschild mass is zero and as r→0 the asymptotic has the de Sitter core. Thermodynamics of magnetically charged black holes in Anti-de Sitter spacetime in an extended phase space, where the cosmological constant is treated as a pressure and the black hole mass is considered as the chemical enthalpy, is studied. It is shown that the black hole thermodynamics mimics the Van der Waals liquid–gas thermodynamics. The magnetic potential and vacuum polarization are calculated. We formulate the first law of black hole thermodynamics and proof that the generalized Smarr relation holds. The critical specific volume, temperature and pressure are evaluated and the critical behaviour of black holes is investigated. We calculate and study the Gibbs free energy and show that phase transitions take place. The local stability are studied by calculating the heat capacity. The black hole Joule–Thomson adiabatic expansion, cooling and heating phase transitions are investigated. We evaluate the Joule–Thomson coefficient and the inversion temperature.

Microscopic investigation of the Johari-Goldstein relaxation in cumene: Insights on the mosaic structure in a van der Waals liquid

The Johari-Goldstein (βJG) relaxation anticipates in time, and is closely connected to, the structural relaxation in deeply supercooled liquids. Probing its microscopic properties is a crucial step for a complete understanding of the glass-transition. We here report the investigation of the van der Waals glass-former cumene using time-domain interferometry, a technique able to probe microscopic density fluctuations at the spatial and temporal scales relevant for the βJG-relaxation. We find that the molecules participating in it undergo a restricted motion, though sufficient to induce local, cage-breaking events at the characteristic time-scale for molecular re-orientations. A detailed characterization of the relaxation strength, i.e. the fraction of molecules involved in the relaxation process, shows that such molecules are connected in a percolating cluster which, above the glass-transition temperature, Tg, is weakly dependent on temperature. Our results confirm thus previous observations of a mosaic structure associated to the βJG-relaxation in the supercooled state, and provide additional information on its temperature evolution above the glass-transition temperature. We conclude that the observed microscopic properties of the βJG-relaxation, and thus of the associated mosaic structure, are generic and independent of the molecular interaction potential. In addition, we show that, while the dynamics within the percolating cluster becomes progressively slower on approaching Tg, the fraction of the molecules involved in cage-breaking events within the βJG-relaxation is not affected by temperature.

Collective dynamics and self-motions in the van der Waals liquid tetrahydrofuran from meso- to inter-molecular scales disentangled by neutron spectroscopy with polarization analysis.

By using time-of-flight neutron spectroscopy with polarization analysis, we have separated coherent and incoherent contributions to the scattering of deuterated tetrahydrofuran in a wide scattering vector (Q)-range from meso- to inter-molecular length scales. The results are compared with those recently reported for water to address the influence of the nature of inter-molecular interactions (van der Waals vs hydrogen bond) on the dynamics. The phenomenology found is qualitatively similar in both systems. Both collective and self-scattering functions are satisfactorily described in terms of a convolution model that considers vibrations, diffusion, and a Q-independent mode. We observe a crossover in the structural relaxation from being dominated by the Q-independent mode at the mesoscale to being dominated by diffusion at inter-molecular length scales. The characteristic time of the Q-independent mode is the same for collective and self-motions and, contrary to water, faster and with a lower activation energy (≈1.4 Kcal/mol) than the structural relaxation time at inter-molecular length scales. This follows the macroscopic viscosity behavior. The collective diffusive time is well described by the de Gennes narrowing relation proposed for simple monoatomic liquids in a wide Q-range entering the intermediate length scales, in contraposition to the case of water.

Non-simple flow behavior in a polar van der Waals liquid: Structural relaxation under scrutiny.

The non-exponential character of the structural relaxation is considered one of the hallmarks of the glassy dynamics, and in this context, the relatively narrow shape observed by dielectric techniques for polar glass formers has attracted the attention of the community for long time. This work addresses the phenomenology and role of specific non-covalent interactions in the structural relaxation of glass-forming liquids by the study of polar tributyl phosphate. We show that dipole interactions can couple to shear stress and modify the flow behavior, preventing the occurrence of the simple liquid behavior. We discuss our findings in the general framework of glassy dynamics and the role of intermolecular interactions.

Phenol, the simplest aromatic monohydroxy alcohol, displays a faint Debye-like process when mixed with a nonassociating liquid.

Solvated in propylene carbonate, viscous phenol is studied using dielectric spectroscopy and shear rheology. In addition, several oxygen-17 and deuteron nuclear magnetic resonance (NMR) techniques are applied to specifically isotope labeled equimolar mixtures. Quantum chemical calculations are used to check the electrical field gradient at phenol's oxygen site. The chosen combination of NMR methods facilitates the selective examination of potentially hydrogen-bond related contributions as well as those dominated by the structural relaxation. Taken together the present results for phenol in equimolar mixtures with the van der Waals liquid propylene carbonate provide evidence for the existence of a very weak Debye-like process that originates from ringlike supramolecular associates.

Simulation of van der Waals liquid droplets within a hot air atmosphere using the smoothed particle hydrodynamics method

The mass and heat transfer of van der Waals liquid droplets within a hot air atmosphere in microgravity have been studied using adaptive Smoothed Particle Hydrodynamics by assuming that the gas atmosphere is in contact with a thermal reservoir for a single-component two-dimensional system. A better definition of the diffuse interface between the phases was obtained through the introduction of a Korteweg tensor. As in previous works, the best initial particle distribution was obtained using the process of spinodal decomposition. The temperature obtained from the van der Waals cycle was compared with the temperature that arises from the integration of the conservation laws that contain the heat-flux vector. The calculated temperature profiles are the same for both the liquid and gas phases. The interface satisfies the condition of coexistence between the phases. In addition, the mass and heat transfer rates as well as the decrease of the drop radius were obtained for the three temperatures studied, finding that these are enhanced as the temperature of the reservoir is increased. Finally, it was possible to observe a damped oscillatory behavior of the temperature between the liquid phase and the interface for the first instants of time. We conclude that this is the mechanism by which the areas with lower temperature within the drop are heated before starting the mass transfer between the liquid and the gas phase.

AdS Black Holes in the Framework of Nonlinear Electrodynamics, Thermodynamics, and Joule–Thomson Expansion

The thermodynamics and phase transitions of magnetic Anti-de Sitter black holes were studied. We considered extended-phase-space thermodynamics, with the cosmological constant being a thermodynamic pressure and the black hole mass being treated as a chemical enthalpy. The extended-phase-space thermodynamics of black holes mimic the behavior of a Van der Waals liquid. Quantities conjugated to the coupling of nonlinear electrodynamics (NED) and a magnetic charge are obtained. Thermodynamic critical points of phase transitions are investigated. It was demonstrated that the first law of black hole thermodynamics and the generalized Smarr relation hold. The Joule–Thomson adiabatic expansion of NED-AdS black holes is studied. The dependence of inversion temperature on pressure and the minimum of the inversion temperature are found.

A Relation between the Formation of a Hydrogen-Bond Network and a Time-Scale Separation of Translation and Rotation in Molecular Liquids.

We study the relation between the translational and rotational motions of liquids, which is anticipated in the framework of the Stokes-Einstein-Debye (SED) treatment. For this purpose, we exploit the fact that 1H field-cycling nuclear magnetic resonance relaxometry and molecular dynamics simulations provide access to both modes of motion. The experimental and computational findings are fully consistent and show that the time-scale separation between translation and rotation increases from the van der Waals liquid o-terphenyl over ethylene glycol to the hydrogen-bonded liquid glycerol, indicating an increasing degree of breakdown of the SED relation. Furthermore, the simulation results for two ethylene glycol models with different molecular conformations indicate that the translation is more retarded than the rotation when the density of intermolecular hydrogen bonds increases. We conclude that an increasing connectivity of a hydrogen-bond network leads to an increasing time-scale separation and, thus, to a stronger SED violation.

Effectiveness of selective area growth using van der Waals h-BN layer for crack-free transfer of large-size III-N devices onto arbitrary substrates

Selective Area van der Waals Epitaxy (SAVWE) of III-Nitride device has been proposed recently by our group as an enabling solution for h-BN-based device transfer. By using a patterned dielectric mask with openings slightly larger than device sizes, pick-and-place of discrete LEDs onto flexible substrates was achieved. A more detailed study is needed to understand the effect of this selective area growth on material quality, device performance and device transfer. Here we present a study performed on two types of LEDs (those grown on h-BN on patterned and unpatterned sapphire) from the epitaxial growth to device performance and thermal dissipation measurements before and after transfer. Millimeter-size LEDs were transferred to aluminum tape and to silicon substrates by van der Waals liquid capillary bonding. It is shown that patterned samples lead to a better material quality as well as improved electrical and optical device performances. In addition, patterned structures allowed for a much better transfer yield to silicon substrates than unpatterned structures. We demonstrate that SAVWE, combined with either transfer processes to soft or rigid substrates, offers an efficient, robust and low-cost heterogenous integration capability of large-size devices to silicon for photonic and electronic applications.

Dipole-dipole correlations and the Debye process in the dielectric response of nonassociating glass forming liquids.

The nonexponential shape of the α process observed in supercooled liquids is considered as one of the hallmarks of glassy dynamics and has thus been under study for decades, but is still poorly understood. For a polar van der Waals liquid, we show here-in line with a recent theory-that dipole-dipole correlations give rise to an additional process in the dielectric spectrum slightly slower than the α relaxation, which renders the resulting combined peak narrower than observed by other experimental techniques. This is reminiscent of the Debye-process found in monohydroxy alcohols. The additional peak can be suppressed by weakening the dipole-dipole interaction via dilution with a nonpolar solvent.

Polymorphic phase transition in liquid and supercritical carbon dioxide

We present experiments on molecular density fluctuations in liquid and supercritical (SC) CO2 using small-angle neutron scattering. Thermal density fluctuations in SC-CO2 determine susceptibility and correlation length identifying the Widom line at their maxima. Droplet formation occurs at the gas–liquid line and between 20 and 60 bar above the Widom line, the corresponding borderline identified as the Frenkel line. The droplets start to form spheres of constant radius of ≈ 45 Å and transform into rods and globules at higher pressure. Droplet formation represents a liquid–liquid (polymorphic) phase transition of the same composition but different density, whose difference defines its order parameter. Polymorphism in CO2 is a new observation stimulating interesting discussions on the topics of gas-like to liquid-like transition in SC fluids and polymorphism since CO2 represents a “simple” van der Waals liquid in contrast to water, which is the most widely studied liquid showing polymorphism in its supercooled state.

Study on the glass transition dynamics and crystallization kinetics of molecular liquid, dimethyl phthalate, confined in Anodized Aluminum Oxide (AAO) nanopores with Atomic Layer Deposition (ALD) coatings

The properties of liquids under geometrical confinement are affected by a subtle counterbalance between the genuine confinement effect and surface conditions. Therefore, depending on the interactions of the guest molecules with the solid surface, the effect caused by increasing geometrical constraints might be diversified. In this work, using Dielectric Spectroscopy (DS) and Differential Scanning Calorimetry (DSC), we aim to examine the effect of surface modification on the glassy dynamics and crystallization tendency of van der Waals liquid - dimethyl phthalate - embedded within cylindrical nanopores. The inner surface of the pore walls was modified by Atomic Layer Deposition (ALD) using two oxide coatings of much different hydrophilicity, namely, alumina oxide (Al2O3) and hafnium oxide (HfO2). The analysis of experimental data revealed that the changes in the surface conditions produced by both types of ALD coatings do not affect significantly the average time of the α-relaxation and the values of the glass transition temperatures for the interfacial and core layers as compared to native nanopores. However, the distribution of the α-relaxation time clearly broadens in the presence of more hydrophobic HfO2 coating. Finally, we also show that the changes in the hydrophilic-hydrophobic nature of the pores can be used to control the crystallization tendency of the nano-confined liquid. We found that with increasing the hydrophobic character of the surface crystallization rates increase while the values of the Avrami parameter decrease.

P–v criticality and heat engine efficiency for Bardeen Einstein–Gauss–Bonnet AdS black hole

In this paper, we discuss the P–v criticality and the heat engine efficiency in the Bardeen Einstein–Gauss–Bonnet (EGB) AdS black hole space–time. From the P–v plane in the extended phase space, we find that the Bardeen EGB-AdS black hole conforms to Van der Waals (VdW) liquid–gas systems in the extended phase space, and of the Bardeen EGB-AdS black hole system is between 0.3333 of the Gauss–Bonnet AdS black hole system and 0.375 of the VdW gas system in the 5-dimensions. Then we construct a heat engine by taking the Bardeen EGB-AdS black hole as the working substance, and consider a rectangle heat cycle in the P–v plane. We find that two cases with different Bardeen parameter e and Gauss–Bonnet parameter α both have the same situation, i.e. as the entropy difference between small black hole S1 and large black hole S2 increases, the heat engine efficiency will increase. Furthermore, as the Bardeen parameter e increases, the efficiency will decrease. However, for the Gauss–Bonnet parameter α, the result is contrary. By comparing with the well-know Carnot heat engine efficiency, we have found the efficiency ratio η/ηc versus entropy S2 is bounded below 1, so it is coincided with the thermodynamical second law.

Coarse graining Euler-Lagrange simulations of cohesive particle fluidization

Although Euler-Lagrange simulations can be performed with millions of particles, particle coarsening where particles are replaced by parcels is necessary for simulation of large particulate and fluid-particle flows. The present study examines coarsening strategies for cohesive particles, where cohesion arises through either van der Waals interaction or liquid bridges between particles. In the latter case, the dynamics of liquid transfer between particles is also taken into account. Strategies based on matching dimensionless overlap, stress and effective coefficient of restitution are shown to lead to same coarse graining rules, while that based on matching the Bond number yields a different set of rules. Test simulations involving fluidization of cohesive particles reveal that the stress-based coarse graining rules provide better approximation of the average slip velocity between the gas and the particles.

Experimental Evidence for a State-Point-Independent Density-Scaling Exponent in Ionic Liquids.

This Letter addresses a fundamental issue of condensed-matter physics, which is the validity of the density-scaling concept. For this purpose, the ambient and high-pressure conductivity measurements of two selected ionic liquids (ILs), with the different contribution of H-bonding interactions, were performed in the dynamic range of 13 orders of magnitude and corresponding to the density changes as large as 20%. All experimental data obtained within one compound are shown to superimpose each other when plotted as a function of ρ^{γ}/T. These results clearly show that for studied ILs the scaling exponent is a state-point-independent parameter that is in odds with the recent findings for van der Waals liquid [Sanz etal., Phys. Rev. Lett. 122, 055501 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.055501].

Isochronal superpositioning in the equilibrium regime of superpressed propylene carbonate to ∼ 1.8 GPa: A study by diffusivity measurement of the fluorescent probe Coumarin 1

We address the problem of glass-forming of liquids by superpressing. We study the pressure-induced dynamic change of the fragile van der Waals liquid propylene carbonate towards the glassy state in the equilibrium regime by measuring the diffusivity of the fluorescent probe Coumarin 1 embedded in the host liquid. The probe diffusivity is measured by the fluorescence recovery after photobleaching (FRAP) technique across a bleached volume generated by the near-field diffracted pattern of a laser beam. The recovered fluorescence intensity fits to a stretched exponential with the diffusive time [Formula: see text] and the stretched exponent [Formula: see text] as free parameters. In the pressure range [0.3-1.0]GPa the diffusivity decouples from the Stokes-Einstein relation. The decoupling correlates well to a decrease of [Formula: see text]. The variation of [Formula: see text] is non-monotonous with [Formula: see text] showing a minimum at [Formula: see text] s. We evidence an isochronal superpositioning over about 3 decades of [Formula: see text] between ∼ 10 s and [Formula: see text] s and a density scaling in the whole investigated pressure range. The pressure at which [Formula: see text] is minimum coincides to the dynamical crossover pressure measured by other authors. This crossover pressure is compatible with the critical point of MCT theory. As our studied pressure range encompasses the critical pressure, the non-monotonous variation of [Formula: see text] opens new insight in the approach to the critical point.

Criticality associated with the variation of the Lovelock parameter

Criticality of Lovelock AdS black holes is investigated from a completely new perspective. Instead of viewing the cosmological constant as a variable, we treat the Lovelock parameter α as a variable and study the corresponding T–r+ criticality and T–S criticality. Specifically, we consider the seven-dimensional uncharged spherical Lovelock AdS black holes as an example. We obtain the analytical expression for the critical Lovelock parameter αc, which only depends on the cosmological constant Λ. The curves of Hawking temperature for the case α<αc exhibits similar behavior as the case Q<Qc observed in charged AdS black holes and is analogous to the van der Waals liquid–gas system. Moreover, we confirm our findings via the techniques of free energy analysis and specific heat analysis. Our research further supports the conjecture that the Lovelock parameter α plays similar role as the electric charge in the criticality of Lovelock AdS black holes.

Nano-viscosity of supercooled liquid measured by fluorescence correlation spectroscopy: Pressure and temperature dependence and the density scaling

The Stokes-Einstein relation allows us to calculate apparent viscosity experienced by tracers in complex media on the basis of measured self-diffusion coefficients. Such defined nano-viscosity values can be obtained through single particle techniques, like fluorescence correlation spectroscopy (FCS) and particle tracking (PT). In order to perform such measurements, as functions of pressure and temperature, a new sample cell was designed and is described in this work. We show that this cell in combination with a long working distance objective of the confocal microscope can be used for successful FCS, PT, and confocal imaging experiments in broad pressure (0.1-100 MPa) and temperature ranges. The temperature and pressure dependent nano-viscosity of a van der Waals liquid obtained from the translational diffusion coefficient measured in this cell by means of FCS obeys the same scaling as the rotational relaxation and macro-viscosity of the system.

Critical behavior and phase transition of dilaton black holes with nonlinear electrodynamics

In this paper, we take into account the dilaton black hole solutions of Einstein gravity in the presence of logarithmic and exponential forms of nonlinear electrodynamics. First of all, we consider the cosmological constant and nonlinear parameter as thermodynamic quantities which can vary. We obtain thermodynamic quantities of the system such as pressure, temperature and Gibbs free energy in an extended phase space. We complete the analogy of the nonlinear dilaton black holes with the Van der Waals liquid–gas system. We work in the canonical ensemble and hence we treat the charge of the black hole as an external fixed parameter. Moreover, we calculate the critical values of temperature, volume and pressure and show that they depend on the dilaton coupling constant as well as on the nonlinear parameter. We also investigate the critical exponents and find that they are universal and independent of the dilaton and nonlinear parameters, which is an expected result. Finally, we explore the phase transition of nonlinear dilaton black holes by studying the Gibbs free energy of the system. We find that in the case of T>T_c, we have no phase transition. When T=T_c, the system admits a second-order phase transition, while for T=T_mathrm{f}<T_c the system experiences a first-order transition. Interestingly, for T_mathrm{f}<T<T_c we observe a zeroth-order phase transition in the presence of a dilaton field. This novel zeroth-order phase transition occurs due to a finite jump in the Gibbs free energy which is generated by the dilaton–electromagnetic coupling constant, alpha , for a certain range of pressure.