One-component Liquid Research Articles

Crystallization and the liquid-liquid critical point in nonbonded modified-WAC models.

For decades, it has been known that Liquid-Liquid Critical Points (LLCPs) can exist in one-component liquids, yet a comprehensive understanding of the conditions under which they arise remains elusive. To better comprehend the possible interplay between the LLCP and the crystalline phase, we conduct molecular dynamics simulations using the nonbonded family of modified-WAC (mWAC) models, which are known to exhibit a LLCP for certain parameter values. By comparing different versions of the mWAC model-those featuring a LLCP and those lacking one-we identify several key differences between the models relating to crystallization. Those models that do have a LLCP are found to have multiple stable crystalline phases, one of them being a solid-state ionic conductor similar to superionic ice. Moreover, we find that for models that do not have a LLCP, the liquid becomes a glass at a larger range of temperatures, possibly preventing the occurrence of a LLCP. Further studies are required to determine if these results are general or model-specific.

Cavitation in a binary Lennard–Jones mixture: van der Waals gradient theory and molecular dynamics simulation

The size dependence of the surface tension of critical bubbles in a superheated (stretched) Lennard–Jones solution with complete solubility of the components is considered. Two approaches are used to determine this dependence. The first one is based on the van der Waals gradient theory, and the second one is based on molecular dynamic simulation results of nucleation in a solution. It is established that, unlike in a one-component liquid, where the surface tension of the equilibrium bubble is less than that for the flat interface, in solution, it can exceed the flat limit. The ranges of temperatures, pressures, and mixture compositions, where this effect occurs, are determined. The asymptotic behavior of the surface tension of vapor phase nuclei within the limits of zero and infinitely large curvature of the dividing surface is analyzed.

Dilution and packing of anionic liquid surfactant in presence of divalent and trivalent counter-ions

Alkyl ether carboxylates are part of a new class of ionic liquids based on the Concept of Melting Point Lowering due to Ethoxylation (COMPLET) and possess unique aggregation behaviour due to the simultaneous anionic and non-ionic nature of the surfactant anion. Previous publications on H[C8E8c] (Polyoxyethylene(8) octyl ether carboxylic acid) and its monovalent salts have shown a variety of phases in aqueous systems with a transition from small spherical micelles at high water contents towards a phase of interdigitated head groups at low water contents. In the present paper, we examine the shorter homologue H[C8E5c] (Polyoxyethylene(5) octyl ether carboxylic acid) and its di- and trivalent transition and rare earth metal salts using X-ray scattering methods in the small- and wide-angle range (SWAXS). These measurements confirm the presence of spherical micelles in diluted aqueous systems which aggregate and whose head groups interdigitate at higher concentrations of the isotropic, non-birefringent ionic liquid. Swelling experiments yield two-dimensional swelling of the microstructure, and combined with the scattering pattern, the data infer prolate spheroidal direct (o/w) micelles with interdigitated head groups, which align to form short linear chains. These chains are offset to form a localised hexagonal close-like packing of the micelles. Most interesting, within this packing, the metal cations are confined into channels between the micelles in linear chains with ion-ion distances of 0.4–1.1 nm. In particular, in the water-free ionic liquid, this confinement may be responsible for some of the unique properties of these systems. It is suggested that the confinement of the cations leads to strong ion-ion aggregation that could be at the origin of the very peculiar magnetic properties of these simple one-component liquids, which contrasts with classical ferrofluids, in which magnetic nanoparticles are dispersed in another liquid.

The Impact of Geometric Parameters on Three-Layer Flow Patterns in a Horizontal Channel: A Comprehensive Study

This paper focuses on studying stationary flows in horizontal layers, taking into consideration the effects of heat and mass transfer. A mathematical model is presented for a three-layer flow in an infinite channel with solid, impermeable walls. The gas-vapor mixture flows over one-component immiscible liquids in the lower and middle layers. The paper considers the processes of heat and mass transfer at the "liquid-gas" and "liquid-liquid" thermocapillary boundaries, respectively. The Dufour and Soret effects are also considered in the upper layer of the system. Mathematical modeling is based on exact solutions of a special form of the Navier-Stokes equations in the Boussinesq approximation. The procedure for determining unknown parameters is explained. The paper derives dependencies of the longitudinal temperature gradients at the system boundaries from each other. The influence of the flow region's geometry on the nature of the process is studied using the "silicone oil-water-air" system as an example. The paper presents longitudinal velocity profiles and temperature distribution for different values of the liquid layer heights while other parameters of the system remain fixed. The paper concludes that, in this case, the thickness of the lower layer is more influential than the thickness of the middle layer.

About the current flow in a discharge tube with a metal section. I-model of a conductive liquid

The work is devoted to the study of the current flow through a glass cylindrical discharge tube with a metal section. A hydrodynamic model of a one-component conductive liquid is considered. The parameters of the conductive liquid are set in accordance with the parameters of the discharge in neon at a pressure of 1 Torr and a current of 10 mA. It is shown that the presence of a metal section leads to a branching of the discharge current into a component flowing through the gas volume and a component flowing along the approximately equipotential metal surface. Two-dimensional distributions of the electric potential, electric field, and current density are obtained depending on the size of the metal section and the radius of the discharge tube. Based on the calculated electric field, the spatial distribution of excitation sources describing the emission of spectral lines and ionization is calculated. The occurrence of a space charge near the glass-metal interface is analysed.

The effect of intra-molecular bonds on the liquid-liquid critical point in modified-WAC models.

To obtain a better understanding of liquid-liquid critical points (LLCPs) in one-component liquids, we extend the modified-WAC model by E. Lascaris, Phys. Rev. Lett. 116, 125701 (2016) which is known to have a LLCP. The original WAC model is a model for silica (SiO2) and consists of a mixture of non-bonded Si and O ions. By adding explicit intra-molecular Si-O bonds to the model, we are able to study how several parameters (Si-O bond length, O-Si-O angle, and bond stiffness) affect the existence and location of the LLCP. We find that for this model, only the Si-O bond length has a strong effect on the LLCP, while the bond angle and bond stiffness have no significant effect on the LLCP. An analysis of the relevant coordination numbers indicates that increasing the bond length decreases the ratio RSi/O of additional Si ions per additional O ion in the first coordination shell of the Si, which causes the LLCP to move to higher, more accessible temperatures. The behavior of the RSi/O parameter shows a strong correlation with the behavior of the LLCP and might be a useful tool to determine if a LLCP exists at low, hard-to-reach temperatures in other models.

The Phase Behavior of a Mixture of the Ionic Liquids [C8mim][AzoO] and [C8mim][PF6

Abstract Mixtures of the ionic liquids 1-methyl-3-octylimidazolium phenylazophenolate, abbreviated as [C8mim][AzoO] and 1-methyl-3-octylimidazolium hexafluorophosphate, abbreviated as [C8mim][PF6], have been known as smart materials with high moldability, electric conductivity, and self-healing properties. However, the structure and the phase behavior at low temperature are not well known in detail, which may change depending on the composition. Differential scanning calorimetry shows that a tiny amount of water is required for the crystallization of neat [C8mim][AzoO]. X-ray diffraction profiles indicate the coexistence of the crystalline phase and the liquid state for the one-component ionic liquid. Polarized optical microscopy indicates that the crystalline phase comprises needle-like microcrystals and coarse crystals. As a result, the phase diagram of the mixture [C8mim][AzoO]n[PF6]1−n is established. The mixture undergoes a complex phase behavior containing glass transition and crystallization, which drastically changes depending on the composition. Noteworthy, it is indicated that [C8mim][PF6] promotes the formation of microcrystals of [C8mim][AzoO], but not coarse crystals. On the other hand, [C8mim][AzoO] facilitates the supercooling of the liquid [C8mim][PF6]. These asymmetric effects enable [C8mim][AzoO]n[PF6]1−n to display moldable but electroconductive features.

Classical bridge functions in classical and quantum plasma liquids

Bridge functions, the missing link in the exact description of strong correlations, are indirectly extracted from specially designed molecular dynamics simulations of classical one-component plasma liquids and accurately parameterized. Their incorporation into an advanced integral equation theory description of Yukawa one-component plasma liquids and a novel dielectric formalism scheme for quantum one-component plasma liquids lead to an unprecedented agreement with available molecular dynamics simulations and new ab initio path integral Monte Carlo simulations, respectively.

Spinodal limits of supercooled liquid Al deduced from configuration heredity of crystal clusters

Whether one-component supercooled liquid encounters a spinodal limit at a sufficiently low temperature has been a controversial issue. To explore the homogeneous nucleation limit (HNL) in liquid Al, a series of molecular dynamics simulations have been performed, and a unique technique able to distinguish the critical nucleus from various embryos has been adopted to measure the crystal nucleation time τN of supercooled liquids and evaluate the nucleation energy barrier ΔEcri∗ in isothermal crystallization. The estimated kinetic spinodal (i.e., HNL) temperature Tks and thermodynamic spinodal temperature Tts are 0.51 Tm and 0.45 Tm, respectively. At the HNL, the nucleation energy barrier ΔEcri∗ is discovered to be very small, and a critical slowdown behavior is also observed near Tks. A careful analysis for the Stokes-Einstein (SE) relation reveals the temperature TSE of SE relation breakdown is only 0.02 Tm higher than Tks, and the occurrence of HNL is not affected by whether the SE relation breaks down or not. These results are consistent with previous reports. To some extent, the small gap between TSE and Tks can be attributed to a weak glass formation ability of liquid Al.

Preparation of one-component addition-cure liquid silicone rubber coating with enhanced storage stability and bond strength

It is of great interest and challenge to simultaneously improve the storage stability and bond strength of one-component addition-cure liquid silicone rubber (OLSR) coating for electronic circuit board. In this work, we proposed an efficient approach to address this issue by incorporating both cyano-modification platinum catalyst (CN–PT) and urethane-containing poly(hydromethylsiloxane) (N-PHMS) into OLSR coating using a mechanical mixer. The CN–PT and N-PHMS were synthesized through thermal polymerization reaction and hydrosilylation reaction, respectively. The OLSR coating containing 0.3 phr CN–PT and 3 phr N-PHMS showed the best properties, with a tensile bond strength of 1.63 MPa, a storage period > 180 d at 25 °C, and a curing rate < 2 h at 80 °C. The salt-spray resistance and continuous power-on performance of OLSR coating were also improved, compared with pure OLSR coating. The synergism of CN–Pt and N-PHMS on the enhancement of both the storage stability and bond strength of OLSR coating was also explored. Our findings exhibited great potentials for fabricating OLSR coating with excellent long-term stable service performance including high storage stability and protective ability.

Dendritic growth of ice crystals: a test of theory with experiments

Motivated by an important application of dendritic crystals in the form of an elliptical paraboloid, which widely spread in nature (ice crystals), we develop here the selection theory of their stable growth mode. This theory enables us to separately define the tip velocity of dendrites and their tip diameter as functions of the melt undercooling. This, in turn, makes it possible to judge the microstructure of the material obtained as a result of the crystallization process. So, in the first instance, the steady-state analytical solution that describes the growth of such dendrites in undercooled one-component liquids is found. Then a system of equations consisting of the selection criterion and the undercooling balance that describes a stable growth mode of elliptical dendrites is formulated and analyzed. Three parametric solutions of this system are deduced in an explicit form. Our calculations based on these solutions demonstrate that the theoretical predictions are in good agreement with experimental data for ice dendrites growing at small undercoolings in pure water.

Surprising peculiarities of the shear viscosity for water and alcohols

This work is devoted to the discussion of surprising behavior of the kinematic shear viscosities for water, methanol and ethanol properties ethanol – one of monohydric alcohols of methanol series. We will show that the application of the standard activation approach to them is conjugated with insuperable difficulties. In order to describe the behavior of the shear viscosity in them the approach, developed for low-molecular argon-like liquids is used. The non-spherical shape of alcohol molecules is taken into account. The special attention is focused to the shear viscosity of aqueous solutions of ethanol, demonstrating a strong dependence on alcohol concentration. A new approach, generalizing that for one-component liquids, is proposed. The careful comparison with experimental data supports our main assumptions.

An Aminopyridinium Ionic Liquid: A Simple and Effective Bifunctional Organocatalyst for Carbonate Synthesis from Carbon Dioxide and Epoxides.

An aminopyridinium ionic liquid is presented as a green, tunable, and active metal-free one-component catalytic system for the atom-efficient transformation of oxiranes and CO2 to cyclic carbonates. Inclusion of a positively charged moiety into aminopyridines, through a simple single-step synthesis, provides a one-component ionic liquid catalytic system with superior activity; effective in ring opening of epoxide, CO2 inclusion, and stabilization of oxoanionic intermediates. An efficiency assessment of a variety of positively charged aminopyridines was pursued, and the impact of temperature, catalyst loading, and the kind of nucleophile on the catalytic performance was also investigated. Under solvent-free conditions, this bifunctional organocatalytic system was used for the preparation of 18 examples of cyclic carbonates from a broad range of alkyl- and aryl-substituted oxiranes and CO2 , where up to 98 % yield and high selectivity were achieved. DFT calculations validated a mechanism in which nucleophilic ring-opening and CO2 inclusion occur simultaneously towards cyclic carbonate formation.

Self-assembly of a triply periodic continuous mesophase with Fddd symmetry in simple one-component liquids.

Triply periodic continuous morphologies (networks) arising as a result of the microphase separation in block copolymer melts have so far never been observed self-assembled in systems of particles with spherically symmetric interaction. We report a molecular dynamics simulation where two simple one-component liquids form upon cooling an equilibrium network with the Fddd space group symmetry. This complexity reduction in the liquid network formation in terms of the particle geometry and the number of components evidences the generic nature of this class of phase transition, suggesting opportunities for producing these structures in a variety of new systems.

Quantum ion thermodynamics in liquid interiors of white dwarfs

ABSTRACT We present an accurate analytic approximation for the energy of a quantum one-component Coulomb liquid of ions in a uniform electron background that has been recently calculated from first principles. The approximation enables us to develop in an analytic form a complete thermodynamic description of quantum ions in a practically important range of mass densities at temperatures above crystallization. We show that ionic quantum effects in liquid cores of white dwarfs (WDs) affect heat capacity, cooling, thermal compressibility, pulsation frequencies, and radii of sufficiently cold WDs, especially with relatively massive helium and carbon cores.

Luttinger liquid and charge density wave phases in a spinless fermion wire on a semiconducting substrate

An interacting spinless fermion wire coupled to a three-dimensional (3D) semiconducting substrate is approximated by a narrow ladder model (NLM) with varying number of legs. We compute density distributions, gaps, charge-density-wave (CDW) order parameters, correlation functions, and the central charge using the density-matrix renormalization group method. Three ground-state phases are observed: a one-component Luttinger liquid, a quasi-one-dimensional (1D) CDW insulator, and a band insulator. We investigated the convergence of the NLM properties with increasing number of legs systematically and confirm that the NLM is a good approximation for the quasi-1D phases (Luttinger liquid and CDW) of the 3D wire-substrate model. The quantum phase transitions between these phases are investigated as function of the coupling between wire and substrate. The critical nearest-neighbor interaction increases with increasing coupling between wire and substrate and thus the substrate stabilizes the Luttinger liquid in the wire. Our study confirms that a Luttinger liquid or CDW insulator phase could occur in the low-energy properties of atomic wires deposited on semiconducting substrates.

Exploring “Dormant” Opto-Mechanical Properties of the Isotropic Phase of Liquid Crystals and Revealing Hidden Elasticity of (Ordinary) Liquids

There is little literature on the flow properties of the isotropic phase of liquid crystalline fluids. However, this phase is an ideal tool to bridge the physics of liquid crystals with those of (ordinary) fluids. Optical and mechanical studies are presented, demonstrating that away from any phase transition, the isotropic phase of liquid crystalline molecules (LCs) and liquid crystalline polymers (LCPs) can work as an optical oscillator in response to low-frequency mechanical excitation, establishing the elastic origin of the flow birefringence and “visualizing” the very existence of the elastic nature of the liquid state. Additionally, mimicking the excellent anchoring ability of liquid crystals, an alternative rheological protocol optimizing the fluid/substrate interfaces is presented to access the low-frequency shear elasticity in various one-component liquids and salt-free aqueous solutions.

Self-diffusion in single-component Yukawa fluids

It was suggested in the literature that the self-diffusion coefficient of simple fluids can be approximated as a ratio of the squared thermal velocity of the atoms to the ‘fluid Einstein frequency,’ which can thus serve as a rough estimate of the friction (momentum transfer) rate in the dense fluid phase. In this article we test this suggestion using a single-component Yukawa fluid as a reference system. The available simulation data on self-diffusion in Yukawa fluids, complemented with new data for Yukawa melts (Yukawa fluids near the freezing phase transition), are carefully analyzed. It is shown that although not exact, this earlier suggestion nevertheless provides a very sensible way of normalization of the self-diffusion constant. Additionally, we demonstrate that certain quantitative properties of self-diffusion in Yukawa melts are also shared by systems like one-component plasma and liquid metals at freezing, providing support to an emerging dynamical freezing indicator for simple soft matter systems. The obtained results are also briefly discussed in the context of the theory of momentum transfer in complex (dusty) plasmas.

Microscopic Theory of Coupled Slow Activated Dynamics in Glass-Forming Binary Mixtures.

The Elastically Collective Nonlinear Langevin Equation theory for one-component viscous liquids and suspensions is generalized to treat coupled slow activated relaxation and diffusion in glass-forming binary sphere mixtures of any composition, size ratio, and interparticle interactions. A trajectory-level dynamical coupling parameter concept is introduced to construct two coupled dynamic free energy functions for the smaller penetrant and larger matrix particle. A two-step dynamical picture is proposed where the first-step process involves matrix-facilitated penetrant hopping quantified in a self-consistent manner based on a temporal coincidence condition. After penetrants dynamically equilibrate, the effectively one-component matrix particle dynamics is controlled by a new dynamic free energy (second-step process). Depending on the time scales associated with the first- and second-step processes, as well as the extent of matrix-correlated facilitation, distinct physical scenarios are predicted. The theory is implemented for purely hard-core interactions, and addresses the glass transition based on variable kinetic criteria, penetrant-matrix coupled activated relaxation, self-diffusion of both species, dynamic fragility, and shear elasticity. Testable predictions are made. Motivated by the analytic ultralocal limit idea derived for pure hard sphere fluids, we identify structure-thermodynamics-dynamics relationships. As a case study for molecule-polymer thermal mixtures, the chemically matched fully miscible polystyrene-toluene system is quantitatively studied based on a predictive mapping scheme. The resulting no-adjustable-parameter results for toluene diffusivity and the mixture glass transition temperature are in good agreement with experiment. The theory provides a foundation to treat diverse dynamical problems in glass-forming mixtures, including suspensions of colloids and nanoparticles, polymer-molecule liquids, and polymer nanocomposites.

Precision measurements of thermodynamic parameters of heavy alkali metals

On the temperature dependences of a number of one-component liquids, regions of anomalous behavior in the form of kinks and also in the form of limited areas of forced growth have been previously observed (LA Blagonravov, LA Orlov, et al., TVT 2000, vol. 38, No. 4, p.566-572). However, the interpretation of these anomalies is complicated by the small magnitude of the effects themselves (the magnitude of the observed effect was 5%, a random error of 2-3%). An increase in the accuracy of measurements is required for a more confident determination of the detailed shape of the anomalies. In the proposed work, thermodynamic parameters are studied using a technique that uses the elastic-thermal effect. The adiabatic thermal coefficient of pressure (a.t.p.c.) is measured: χ = (1/T)(∂T/∂p)S. An installation in which the pressure change is carried out in a periodic mode is used for measurements. The software allows simultaneous averaging of the values of the amplitude of pressure oscillations and the amplitude of temperature response oscillations with the subsequent determination of their ratio. The facility uses an advanced pressure modulator, which allows creating pressure oscillations of the shape close to sinusoidal (the value of the second harmonic is not more than 10%) and a precision SR-810 nanovoltmeter with a synchronous digital detector. The currently used technique provides an acceptable measurement accuracy (error in the region of 0.5-1%). However, to further increase the accuracy, it was decided to make changes in the measuring path. Namely, by developing and applying a scheme of a precision low-noise preamplifier based on the instrument amplifier INA333, a circuit allowing simultaneous measurement of not only the two above parameters but also the current temperature of the sample (to exclude the effect of temperature drift.) Preliminary results of measurements of the temperature dependence of the a.t.p.c. of liquid cesium in the temperature range up to 500 K. Measurements were made at a frequency of pressure oscillations of 2.51 Hz. The measurements of a.t.p.c. of rubidium are also planned.