Molecular Liquids Research Articles

Solvation dynamics on the diffusion timescale elucidated using energy-represented dynamics theory.

Photoexcitation of a solute alters the solute-solvent interaction, resulting in the nonequilibrium relaxation of the solvation structure, often called a dynamic Stokes shift or solvation dynamics. Thanks to the local nature of the solute-solvent interaction, the characteristics of the local solvent environment dissolving the solute can be captured by the observation of this process. Recently, we derived the energy-represented Smoluchowski-Vlasov (ERSV) equation, a diffusion equation for molecular liquids, which can be used to analyze the solvation dynamics on the diffusion timescale. This equation expresses the time development for the solvent distribution on the solute-solvent pair interaction energy (energy coordinate). Since the energy coordinate can effectively treat the solvent flexibility in addition to the position and orientation, the ERSV equation can be utilized in various solvent systems. Here, we apply the ERSV equation to the solvation dynamics of 6-propionyl-2-dimethylamino naphthalene (Prodan) in water and different alcohol solvents (methanol, ethanol, and 1-propanol) for clarifying the differences of the relaxation processes among these solvents. Prodan is a solvent-sensitive fluorescent probe and is thus widely utilized for investigating heterogeneous environments. On the long timescale, the ERSV equation satisfactorily reproduces the relaxation time correlation functions obtained from the molecular dynamics (MD) simulations for these solvents. We reveal that the relaxation time coefficient on the diffusion timescale linearly correlates with the inverse of the translational diffusion coefficients for the alcohol solvents because of the Prodan-solvent energy distributions among the alcohols. In the case of water, the time coefficient deviates from the linear relationship for the alcohols due to the difference in the extent of importance of the collective motion between the water and alcohol solvents.

Phonon thermophoresis of crystalline nanoparticles in liquids.

Our nonequilibrium thermodynamic model of thermodiffusion in molecular liquid systems is used to examine the role of thermal phonons in the thermophoresis of liquid suspensions of crystalline nanoparticles, which tend to have high thermal conductivity. The Soret coefficient used to characterize stationary thermodiffusion is related to differences in entropy between a particle and the body of liquid that it displaces. Calculated phonon Soret coefficients for graphite and diamond nanoparticles in three polar solvents are used to establish parameters where the phonon mechanism is expected to dominate particle thermophoresis compared to slip-flow caused by forces induced in the surface layer by the temperature gradient. Because the active mode of thermal conductivity in crystals varies with particle size, phonon thermophoresis is expected to dominate within a specific range of particle size, which varies with the properties of the particle and suspending liquid. For graphite and diamond particles in polar solvents the model estimates a size range of around 10-100 nm. Finally, thermophoretic particle accumulation is ultimately limited by the increasing concentration of particles having high thermal conductivity because the zone of particle concentration decreases the local temperature gradient that drives thermophoresis. The respective nonperturbing concentration is evaluated as the function of the size of a given material.

Comparative investigations on α relaxation and conductivity of probe ions in a series of small molecular liquids

The coupling between translational motion and rotational motion in liquids is one of the long-standing concerns in condensed matter physics. The relaxation times of α relaxation and probe ion conductivities in a series of small molecular liquids, 15 types of single and binary small molecular liquids with different molecular shapes and functional groups when the number of carbon atoms is in a range from 3 to 14, are simultaneously obtained by dielectric spectroscopy method in this work. The results indicate that the coupling between translation and rotation is not directly related to the functional group of liquid molecules, nor very sensitive to the shape nor the size of molecules or ion size. However, the microstructure of liquid is a key factor affecting the coupling between translation and rotation. In other words, when the microstructure of the liquid is unchanged, the dependence of relaxation time on temperature is consistent with the dependence of conductivity reciprocal on temperature, whether in single small molecular liquids or in binary small molecular liquids, which provides a method for measuring relaxation time. The research results also show that the temperature dependence of the conductivity of the impurity ions carried by the liquid itself is consistent with the one of quantitatively doped ions, providing the ideas for investigating the ion conductivity behavior in organic small molecular liquids with low electrolyte solubilities. The experimental results of monohydroxy alcohol are consistent with the viewpoint that α relaxation rather than Debye relaxation corresponds to the system structure relaxation.

Electrochemical storage systems: Safer and more sustainable batteries

Lithium-ion batteries (LIBs) are the predominant power source for portable electronic devices, and in recent years their use has extended to higherenergy and larger devices. However, to satisfy the stringent requirements of safety and energy density, further material advancements are required. Due to the inherent flammability of organic solvent-based liquid electrolytes and their instability against materials utilized in high-energy systems, a transition to alternative ionconductive media becomes urgent. In this paper, some possible solutions, shifting from molecular liquids to a class of materials based on ions, such as ionic liquids (ILs), and polymers, such as gel polymer electrolytes (GPEs), will be briefly discussed. Moreover, innovative technologies, the so-called beyond-lithium batteries, will be presented, considering a more sustainable anode material based on calcium.

An innovative method for calculating partial molar volume from a standard molecular trajectory

In this research, we present a novel method for calculating the partial molar volume (PMV) of system components through post-processing the output trajectory of a molecular dynamic simulation. The method involves employing linear regression and sampling small volumes from the system during the simulation time, to obtaining the PMV of its components. To validate our approach, simulations were conducted on two systems previously studied in the Journal of Molecular Liquids (386, 2023, 122498). A comparison between our results and experimental values revealed average relative deviations as minimal as 2.49 %, and specific sampling methods achieved even lower relative deviations, down to 1.21 % and 1.18 %. The average relative deviation across all components for the two systems was calculated at 7.24 %, translating to average deviations of 6.19 cm^3/mol for mesitylene and 7.80 cm^3/mol for isopropanol. To demonstrate the method's implications, we conducted simulations on a series of systems comprising model asphaltene, an organic solvent, and a chemical inhibitor. By analyzing the PMV results for the precipitant phase (asphaltene and inhibitor), we offer insights into the inhibition mechanism, showcasing how it enhances the solubility of the precipitants in the employed solvents. Finally, we aim to hypothesize a molecular-level explanation of the inhibition process through quantitative measures by comparing the size and number of nanoaggregates and exploring the molecular positioning within these aggregates. Our method introduces a valuable approach to calculate PMVs to comprehend the behavior of self-associating solutes and their interactions with solvents.

Improved data analysis for molecular dynamics in liquid CCl4

Previously reported inelastic x-ray scattering spectra of a typical van der Waals molecular liquid CCl4 were reanalyzed using a generalized Langevin formalism with a memory function including a thermal and two viscoelastic relaxation processes and simple sparse modeling. The obtained excitations of longitudinal acoustic phonons show a largely positive deviation from the hydrodynamic value by about 57%, much larger than about 37% by the previously reported damped harmonic oscillator result. Such large values of fast sounds in molecular liquids larger than 15-20% of typical liquid metals are interpreted as extra energy losses for terahertz phonons by molecules' vibrational and rotational motions. The rates of the fast and slow viscoelastic relaxations in the memory function at low Q indicate large values, about 0.5 and 2 ps, which correspond to the vibrational and rotational motions of CCl4 molecules, respectively. These values are larger than those of the typical polar molecular liquid acetone, which may reflect the heavier atomic mass of CCl4. The Q dependences of the viscoelastic relaxation rates are discussed in terms of the lifetime and propagating length of the terahertz phonon oscillations. The microscopic kinematic longitudinal viscosity was obtained from the viscoelastic relaxation magnitudes and times, rapidly decreasing with Q from a macroscopic value at Q→0.

LiNO3-assisted electrochemical extraction of metallic Sm from a molecular liquid-based electrolyte

Developing efficient, green, and cost-effective methods for extracting rare earth (RE) metals is essential to accelerate breakthroughs in critical technologies in the field of RE-based functional materials. In this study, a low-cost aprotic polar molecular liquid, N,N-Dimethylformamide (DMF), was used for electrowinning metallic Sm with upstream SmCl3 as the raw material, inspired by previous applications of diverse specialised ionic liquids for the electrochemical recovery of RE metals. Cyclic voltammetry and electrodeposition experiments demonstrated that metallic Sm cannot be obtained from the binary DMF-SmCl3 system, but can be electrodeposited with LiNO3. Therefore, the mechanism underlying the observed electrochemical behaviour is elucidated and discussed in detail. Sm and Sm–Co metallic elements were successfully electrodeposited on an Al substrate at a relatively high current density, characterised, and evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Moreover, a unique two-step method involving electrodeposition and direct smelting is prospectively described for the continuous preparation of bulk RE-containing alloys to stabilise highly active RE elements. Therefore, this study provides valuable insights into practical solvometallurgical processes for RE metal extraction, refinement, and recycling.

Guest Editorial: Special Issue on Multi-Functional Molecular Liquids, Solids, and Crystals for Materials Engineering & Manufacturing — Part I

Guest Editorial: Special Issue on Multi-Functional Molecular Liquids, Solids, and Crystals for Materials Engineering & Manufacturing — Part I

Aqueous Humor Liquid Biopsy as a Companion Diagnostic for Retinoblastoma: Implications for Diagnosis, Prognosis, and Therapeutic Options: Five Years of Progress

To define the prospective use of the aqueous humor (AH) as a molecular diagnostic and prognostic liquid biopsy for retinoblastoma (RB). This is a prospective, observational study wherein an AH liquid biopsy is performed at diagnosis and longitudinally through therapy for patients with RB. Tumor-derived cell-free DNA is isolated and sequenced for single nucleotide variant analysis of the RB1 gene and detection of somatic copy number alterations (SCNAs). The SCNAs are used to determine tumor fraction (TFx). Specific SCNAs, including 6p gain and focal MycN gain, along with TFx, are prospectively correlated with intraocular tumor relapse, response to therapy, and globe salvage. A total of 26 eyes of 21 patients were included with AH taken at diagnosis. Successful ocular salvage was achieved in 19 of 26 (73.1%) eyes. Mutational analysis of 26 AH samples identified 23 pathogenic RB1 variants and 2 focal RB1 deletions; variant allele fraction ranged from 30.5% to 100% (median 93.2%). At diagnosis, SCNAs were detectable in 17 of 26 (65.4%) AH samples. Eyes with 6p gain and/or focal MycN gain had significantly greater odds of poor therapeutic outcomes (odds ratio = 6.75, 95% CI = 1.06-42.84, P = .04). Higher AH TFx was observed in eyes with vitreal progression (TFx = 46.0% ± 40.4) than regression (22.0 ± 29.1; difference: -24.0; P = .049). Establishing an AH liquid biopsy for RB is aimed at addressing (1) our inability to biopsy tumor tissue and (2) the lack of molecular biomarkers for intraocular prognosis. Current management decisions for RB are made based solely on clinical features without objective molecular testing. This prognostic study shows great promise for using AH as a companion diagnostic. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Simple elaboration of drug-SPION nanocapsules (hybridosomes®) by solvent shifting: Effect of the drug molecular structure and concentration

Drug nanocapsules coated with iron oxide nanoparticles (SPION) were elaborated by the simultaneous nanoprecipitation of the drug and the nanoparticles, through solvent shifting. We examined four drugs: sorafenib, sorafenib tosylate, α-tocopherol and paclitaxel, to cover the cases of molecular solids, ionic solids, and molecular liquids. We first investigated the formation of the drug core in the final mixture of solvents at different concentrations. A Surfactant-Free Micro-Emulsion domain (SFME, thermodynamically stable) was observed at low drug concentration and an Ouzo domain (metastable) at high drug concentration, except for the case of paclitaxel which crystallizes at high concentration without forming an Ouzo domain. When co-nanoprecipitated with the molecular drugs in the Ouzo domain (sorafenib or α-tocopherol), the SPION limited the coalescence of the drug particles to less than 100 nm, forming capsules with a drug encapsulation efficiency of ca 80 %. In contrast, larger capsules were formed from the SFME or when using the ionic form (sorafenib tosylate). Finally, the sorafenib-SPION capsules exhibit a similar chemotherapeutic effect as the free drug on the hepatocellular carcinoma in vitro.

Comments on the calculation of thermodynamic adsorption equilibrium constant using the distribution coefficient in Journal of Molecular Liquids 380 (2023) 121725

This comment discussed the calculation of the standard equilibrium constant thermodynamic parameters about the paper published in Journal of Molecular Liquids 380 (2023) 121725. Recently, Khankhasaeva et al. (2023) published a high academic paper to reveal the adsorption kinetic and thermodynamic regularities of diclofenac (DCF) on Fe2O3-pillared montmorillonites (Fe-PMts). Although the author tries to convert the distribution coefficient (Kd) to the standard equilibrium constant (Ko), the calculation formula is incorrect due to the confusion of adsorbate and adsorbent. This creates dimension for Ko obtained from Eq. (2). In this comment, the origin and background of this kind of error is analyzed and the method for correcting the error is presented. We hope this comment clarifies the essence of calculating the standard equilibrium constant by using the distribution coefficient, so others avoid the propagation of this kind of error.

A Second Glass Transition Observed in Single-Component Homogeneous Liquids Due to Intramolecular Vitrification.

On supercooling a liquid, the viscosity rises rapidly until at the glass transition it vitrifies into an amorphous solid accompanied by a steep drop in the heat capacity. Therefore, a pure homogeneous liquid is not expected to display more than one glass transition. Here we show that a family of single-component homogeneous molecular liquids, titanium tetraalkoxides, exhibit two calorimetric glass transitions of comparable magnitude, one of which is the conventional glass transition associated with dynamic arrest of the bulk liquid properties, while the other is associated with the freezing out of intramolecular degrees of freedom. Such intramolecular vitrification is likely to be found in molecules in which low-frequency terahertz intramolecular motion is coupled to the surrounding liquid. These results imply that intramolecular barrier-crossing processes, typically associated with chemical reactivity, do not necessarily follow the Arrhenius law but may freeze out at a finite temperature.

The shift of excitation spectra at blue edge of emission (BEEmS) as a new methodology to probe heterogeneity

Many current methods for detecting molecular-level heterogeneity are complex and require stringent data analysis, limiting their widespread use. Herein, we propose a novel edge effect, i.e., the shift of excitation spectra at the blue edge of emission (which we termed as Blue Edge Emission Shift, BEEmS), to perceive the structural heterogeneity. This method is simple and can be easily implemented with commonly available fluorimeter. Red edge excitation shift (REES), a related technique, is already in use, but like most other known techniques, its usefulness is constrained by its dependence on environmental rigidity. Our method does not suffer from this drawback significantly. We showed the generality of the proposed method taking various chemically and biologically heterogenous systems including molecular liquid, deep eutectic solvents, organic cavitand, micelle and protein. BEEmS certainly comes out as a more effective sensor of heterogeneity than REES in certain cases (like denatured protein, hydrophobic deep eutectic solvent and SDS micelle) where solvation time is not sufficiently slow to be detected by REES, but can be measured though BEEmS. Furthermore, unlike most existing techniques, domain-specific heterogeneity of a model multi-domain protein is successfully measured.

Discrete Modeling Approach for Cluster-Based Excess Gibbs-Energy of Molecular Liquids.

The excess Gibbs-energy of a two-component liquid molecular mixture is modeled based on discrete clusters of molecules. These clusters preserve the three-dimensional geometric information about local molecule neighborhoods that inform the interaction energies of the clusters. In terms of a discrete Markov-chain, the clusters are used to hypothetically construct the mixture using sequential insertion steps. Each insertion step and, therefore, cluster is assigned a probability of occurring in an equilibrium system that is determined via the constrained minimization of the Helmholtz free energy. For this, informational Shannon entropy based on these probabilities is used synonymously with thermodynamic entropy. A first approach for coupling the model to real molecules is introduced in the form of a molecular sampling algorithm, which utilizes a force-field approach to determine the energetic interactions within a cluster. An exemplary application to four mixtures shows promising results regarding the description of a variety of excess Gibbs-energy curves, including the ability to distinguish between structural isomers.

Glass formation processes in fullerene mixtures

The local structural features of the A20B80 fullerene mixture (where A = C60 and B = C70) are studied by the molecular dynamics simulations for a wide temperature range, including the phase of an equilibrium liquid phase and a supercooled melt, in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Structural and cluster analyzes revealed the presence of icosahedral clusters in the supercooled melt phase and determined the critical glass transition temperature.

Modification of the Stefan’s Rule for the Surface Tension Coefficients of Liquids

A modification of the “Stefan’s rule” for the surface tension coefficients of liquids has been proposed, with the modification consisting in choosing a liquid as a system of comparison with respect to its surface. An expression for the surface tension coefficients has been derived and employed to interpret their temperature dependences for a number of molecular liquids with different physicochemical properties.

Water-induced changes in choline chloride-carboxylic acid deep eutectic solvents properties

Deep eutectic solvents (DES) have become a promising alternative to molecular organic solvents and ionic liquids in a variety of scientific applications. Their customizable physicochemical properties make them attractive for extraction, catalysis, electrochemistry and drug delivery. Recently, the study of not so much DES themselves, as their mixtures with water, has attracted particular interest. In this study, six widely used DESs based on choline chloride and carboxylic acids (citric, tartaric, malic, glycolic, malonic and lactic) with a water content of 0–50 wt% were analyzed. Properties such as density, viscosity, conductivity and spectral properties of DES (IR spectroscopy and refractive index) were studied. The results show that in the entire range of water content under study, there are no abrupt changes in properties for all the studied parameters, which allows us to conclude that water is gradually incorporated into the DES structure without its destruction. However, within this class of eutectic solvents, subclasses can be distinguished, due to various changes in the studied properties. These results provide important information for optimizing the performance of DES in practical applications and highlight their potential as sustainable green solvents in modern science and technology.

Polymer gel electrolytes containing sodium salts with BF4−, ClO4− and CF3SO3− anions immobilized in TEGDME molecular liquid for sodium battery and electric double layer capacitor

The present study reports synthesis and analysis of different characteristics of sodium ion conducting polymer gel electrolytes (PGEs) containing sodium salts with BF4−, ClO4− and CF3SO3− anions dissolved in tetraethylene glycol dimethyl ether and immobilized in a copolymer matrix consisting of polymethyl methacrylate and poly(vinylidene fluoride-co-hexafluoropropylene). The PGE containing the NaBF4 salt could deliver an ionic conductivity of 1.4 × 10−3 S cm−1 at room temperature along with superior dielectric properties as compared to the electrolytes with NaClO4 and NaCF3SO3 salts. The feasibility of designing sodium-based batteries and EDLCs has been demonstrated using the optimized PGE containing NaBF4 salt. The prototype sodium‑sulfur (NaS) battery designed by utilizing the optimized PGE, sodium amalgam anode and sulfur cathode provides open circuit voltage of ∼2.4 V and initial discharge capacity of ∼163 mA h g−1 and 126 mA h g−1 at discharge currents of 33 mA g−1 and 66 mA g−1, respectively. This optimized PGE also demonstrate good compatibility with AC electrodes in electric double layer capacitor (EDLC) application and delivered a significant specific capacity ∼64 F g−1 at 0.5 mA cm−2 current.

Laboratory equipment for practice learning in the framework of educational course “Molecular Physics and Thermodynamics”

This article presents laboratory equipment for practice learning of physics specialties students in the framework of educational course “Molecular Physics and Thermodynamics”. The presented laboratory equipment allows measuring the temperature dependence of the thermal conductivity coefficient of molecular liquids under atmospheric pressure and saturated vapors pressure in the temperature range from 150K to 400K. A general scheme of the developed experimental setup for measuring the thermal conductivity of liquids by the steady-state method under isobaric condition has been described. The created laboratory setup uses general design solutions of the coaxial cylinder method, preserving its features and measurement precision in general. The measurements are carried out on coaxial-geometry cell under atmospheric pressure. A modified heat potentiometer method with one thermometer was used, which allowed us to minimize the error in the estimation of the thermal conductivity coefficient due to the uncontrollable heat flows and different calibration of thermometers. The total systematic error in the measurement of the molecular liquids thermal conductivity does not exceed 3%. The procedures for direct measurement and calculation of the thermal conductivity coefficient of molecular liquids using the developed laboratory equipment are described.

A possible origin of the very fast sound in terahertz region in liquid benzene

Previously reported inelastic X-ray scattering spectra of molecular liquid benzene were reanalyzed by a generalized Langevin formalism (GLF) with a memory function including a thermal and two viscoelastic relaxation processes. A new algorithm was containing a simple sparse modeling to smooth Q dependences of dynamical parameters used in the present GLF analysis. The obtained excitation energies of longitudinal acoustic phonons show a largely positive deviation from the hydrodynamic value by about 50%, the same as that by previous analysis and similar to existing results of several molecular liquids. Such a large deviation of dynamical sound velocity in liquid benzene is interpreted as extra energy-losses for terahertz phonons by vibrational and rotational motions of benzene molecules. The rates of the fast and slow viscoelastic relaxations in the memory function at low Q are undetectable and 0.4-0.8 ps, respectively. These can be explained by the vibrational and anisotropic rotational motions of benzene molecules. The microscopic kinematic longitudinal viscosity rapidly decreases with Q from a reasonable macroscopic value.