Liquid Molecules Research Articles

Enhanced Evaporation of Ultrathin Water Films on Silicon-Terminated Si3N4 Nanopore Membranes.

Water evaporation confined in nanoscale is a ubiquitous phenomenon in nature and has crucial importance in a broad range of technical applications. With the nonequilibrium molecular dynamics simulation, we elucidate nanothin water film evaporation characteristics on a silicon nitride nanopore membrane considering the effects of pore size and pore chemistry. Pore chemistry plays the main role in regulating the evaporation flux. The terminated Si atoms on the pore surface lead to a higher evaporation intensity than the N ones. We attribute this enhancement to the transition of the structural properties of fluid, where liquid molecules are packed loosely and disorderedly under the inducement of terminated silicon atoms. The findings in the present work can contribute to the fundamental understanding of the nanopore-enhanced evaporation process and provide new guidance to the design of advanced nanopore membrane materials.

Computational study of the electrostatic potential and charges of multivalent ionic liquid molecules

The electrostatic interactions in ionic liquids (ILs) can be difficult to quantify, but this information is very valuable for improving intermolecular potentials for performing molecular-level simulations. Although polarizable forcefields can provide improved accuracy, the computational efficiency of fixed charge molecular models is often preferred for larger systems. Here, we propose a multi-scale screening approach for analyzing the charge scaling behavior and other electrostatic properties of ILs, which is more attainable than previous analysis methods that rely on the IL crystalline structures. Based on isolated molecules and small clusters, we study the electrostatic potential properties and charges of multivalent IL molecules using density-functional theory calculations and ab initio molecular dynamics simulations. The charges of the IL molecules are calculated and compared using several different charge estimation techniques. Although there are some differences among the estimated partial charges on the atoms, the total anion and cation charges are very similar. The charge scaling factors are substantial, and they are only slightly affected by the IL cluster size model.

The Role of Pulmonary Surfactant in COVID-19 Understanding

Background: In Covid-19 the virus infects the respiratory tract in human. When lung tissue becomes diseased, the walls and lining of the alveoli and capillaries are damaged. At this point lung compliance and ventilation decrease. Pulmonary surfactant that is produced and dispersed into alveolar space, has a significant role in understanding how heavily covid-19 interferes and infects lung cells. The importance of pulmonary surfactant in alveoli is to lower surface tension at air/liquid interface in the lung. This is achieved by reducing the work of breathing and preventing alveolar collapse. The main constituent of pulmonary surfactant is dipalmitoylphosphatidylcholine (DPPC) (C40H80NO8P). It is a phospholipid containing two non polar palmitic acid C16 chains as hydrophobic tails linked to a polar head group of a phosphatidylcholine (also known as lecithin).
 Rationale of the Review and Objective Method: When DPPC molecules are in contact with a polar solvent, micelles which grow further into bilayers are formed considering their cylindrical structures. This trait makes the whole structure of pulmonary surfactant as amphipathic and surface active molecules. The head group of phosphatidylcholine in the pulmonary surfactant is attracted by polar liquid molecules causing a reduction of the liquid surface tension.
 Conclusion: This review complements the quoted information analysing them theoretically and integrates recent advances in pulmonary surfactant research with the global pandemic.

How coronavirus survives for hours in aerosols.

COVID (CoronaVirus Disease)-19, caused by severe acute respiratory syndrome-CoronaVirus-2 (SARS-CoV-2) virus, predominantly transmits via airborne route, as highlighted by recent studies. Furthermore, recently published titer measurements of SARS-CoV-2 in aerosols have disclosed that the coronavirus can survive for hours. A consolidated knowledge on the physical mechanism and governing rules behind the significantly long survival of coronavirus in aerosols is lacking, which is the subject of the present investigation. We model the evaporation of aerosolized droplets of diameter m. The conventional diffusion-limited evaporation is not valid to model the evaporation of small size (μm–nm) droplets since it predicts drying time on the order of milliseconds. Also, the sedimentation timescale of desiccated droplets is on the order of days and overpredicts the virus survival time; hence, it does not corroborate with the above-mentioned titer-decay timescale. We attribute the virus survival timescale to the fact that the drying of small (m–nm) droplets is governed, in principle, by the excess internal pressure within the droplet, which stems from the disjoining pressure due to the cohesive intermolecular interaction between the liquid molecules and the Laplace-pressure. The model predictions for the temporal reduction in the aerosolized droplet number density agree well with the temporal decay of virus titer. The findings, therefore, provide insight on the survival of coronavirus in aerosols, which is particularly important to mitigate the spread of COVID-19 from indoors.

Effects of surface wettability on contact line motion in liquid–liquid displacement

The behaviors of oil–water–solid interfaces are of basic and applied importance for many fields, such as energy, geochemistry, and biomedical sciences, yet molecular mechanisms are still poorly known. In particular, the traditional adsorption–desorption mechanism based on a single compound does not work to describe the contact line for liquid–liquid–solid systems where the two liquids have similar interactions with the solid surface. Here, we present a series of experiments of water spreading in alkanes, i.e., n-decane, n-dodecane, and n-hexadecane, under various surface wettabilities. The contact line motion is captured by the high-speed camera, allowing us to analyze the friction coefficient, displacement distance and frequency, and activation free energy during the contact line motion via the molecular kinetic theory. We further develop a friction model of contact line motion in liquid–liquid–solid systems by establishing the activation free energy of liquid–liquid–solid systems as a function of the activation free energies of separate one-liquid systems. Results show that the contact line friction coefficients increase with the increasing hydrophobicity (e.g., for n-decane, the coefficient changes from 0.3072 to 2.1967 Pa·s), explained by the increase in the displacement distance and sharp decrease in the displacement frequency of the molecules. Additionally, we find a non-monotonic dependence of the contribution of the surface part to the activation free energy on the wettability, with a maximum percentage of 70%–80% at the intermediate wettability, where the reduced collisions of liquid molecules weaken the molecular adsorption/desorption process. Finally, we find that the correlation coefficient n in our model is affected by the surface wettability, with a maximum at the intermediate wettability, showing a good prediction of the results in the literature. The reason can be attributed to the non-monotonic effects of wettability on the surface part of the activation free energy in two-liquid systems.

Molecular study on the role of solid/liquid interface in specific heat capacity of thin nanofluid film with different configurations

Nanoconfined liquids may have significantly different properties from their bulks. This can be prominent for nanofluids due to the interaction between nanoparticles and solid/liquid interface, which is studied under different configurations (including confined, sessile, and freestanding forms) in the present work by calculating a typical thermophysical property (the specific heat capacity) using the molecular dynamics simulation method. It is found that the copper-water nanofluid film has a relatively higher specific heat capacity than the water film with the same thickness; and the specific heat capacity is closely related to the configuration: the confined nanofluid film has the highest value, followed by the sessile and freestanding nanofluid films. The reason behind this is explored in terms of interface effects: the influence of nanoparticles on the interface energy and hence specific heat capacity is weaker than the plate which has adjacent liquid molecules with highly impacted molecular structure; and compared to the symmetrical density distributions in confined and freestanding films, the asymmetry in the sessile film causes changes of the interfacial parameters including mean square displacement, radial distribution function, and vibration density of state of water molecules. Thus, this work provides insight into the variation of thermophysical properties for nanofluids with various forms of nanoconfinement or configurations in applications such as distillation, evaporation, and interface separation.

Electrophilic and Nucleophilic Modifiers as a Factor of Formation of Lipophilic Properties of Surface-Modified Materials

Stabilization of the functional properties of dispersed and compact solid metals, as well as regulation of their reactivity, improvement of water-repellent, antifriction and anti-corrosion properties by creating the protective films on the surface is an urgent problem of obtaining resource-saving materials. Previously, the research conducted at REC "Nanotechnology" of Mining University proved that chemisorption of ethylhydridesiloxane vapors together with cationic surfactants based on quaternary ammonium compounds has a beneficial effect on the water-repellent properties of metals. In order to obtain the physicochemical substantiation of the effect of hydrophobization of the surface of modified dispersed metals for the first time, the study of the electrophilic-nucleophilic properties of the active substances of the surface modifiers of dispersed and compact metals was carried out using the methods of quantum-chemical modeling in HyperChem software package. The dipole moment, energy of the highest occupied and the lowest unoccupied molecular orbitals, electrophilic-nucleophilic properties were determined. The series of enhancement of nucleophilic/electrophilic properties and dipole moment for modifiers were obtained. The donor-acceptor properties, the differences in the characteristics of the molecules of alkamone (A), triamone (T) and hydrophobic silicone organic liquid were quantitatively and qualitatively established. The patterns of the formation of hydrophobic properties of the surface during the layering of molecules of ammonium and organosilicon compounds with different electrophilic-nucleophilic properties on dispersed metals have been established. Recommendations for the use of modifiers for the production of high - and superhydrophobic materials are proposed.

Promoted Disappearance of CO2 Hydrate Self-Preservation Effect by Surfactant SDS

The capture, storage and utilization of CO2 through hydrate-related technology is a promising approach to addressing the global warming issue. Dissociation is required after the transportation of CO2 gas in the form of a self-preserving hydrate. In order to investigate the dissociation behaviors as the self-preservation effect is removed, CO2 hydrates were frozen, and then the self-preservation effect was removed through uniform heating. An evident dependence of hydrate dissociation duration on the initial dissociation rates after losing the preservation effect was observed. The results in the silica gel powder and sodium dodecyl sulphate solution showed significant reductions in the initial dissociation temperatures and a slight decrease in the initial dissociation rates when compared with those of pure water. The reductions in the former were 2.88, 2.89, and 5.73 °C in silica gel, sodium dodecyl sulphate, and a combination of the two, respectively, while the reductions in the latter were 0.12, 0.12, and 0.16 mmol/min, respectively. As the results are inconsistent with the conventional mechanism elucidating a self-preservation effect, the ice shell theory was hence further supplemented by introducing innovative contribution factors—nonenclathrated liquid water and gas molecules dissolved inside. These findings are expected to provide references for CO2 gas transportation and usage of the self-preservation effect.

Direct Current Electricity Generation from Dynamic Polarized Water–Semiconductor Interface

Liquid electricity generator and hydrovoltaic technology have received numerous attentions, which can be divided into horizontal movement generator and vertical movement generator. The horizontal movement generator is limited for powering the integrated and miniaturized energy chip as the current output direction is depending on the moving direction of the water droplet, which means a sustainable and continuous direct-current (DC) electricity output can be hardly achieved because of the film of limited length. On the other hand, the existing vertical movement generators include triboelectricity or humidity gradient-based liquid electricity generator, where the liquid or water resource must be sustainably supplied to ensure continuous current output. Herein, we have designed an integratable vertical generator by sandwiching water droplets with semiconductor and metal, such as graphene or aluminum. This generator, named as polarized liquid molecular generator (PLMG), directly converts the lateral kinetic energy of water droplet into vertical DC electricity with an output voltage of up to ~1.0 V from the dynamic water-semiconductor interface. The fundamental discovery of PLMG is related to the non-symmetric structure of liquid molecules, such as water and alcohols, which can be polarized under the guidance of built-in field caused by the Fermi level difference between metal and semiconductor, while the symmetric liquid molecules cannot produce any electricity on the opposite. Integratable PLMG with a large output power of ~90 nW and voltage of ~2.7 V has been demonstrated, meanwhile its small internal resistance of ~250 kilohm takes a huge advantage in resistance matching with the impedance of electron components. The PLMG shows potential application value in the Internet of Things (IoTs) after proper miniaturization and integration.

Electrophilic-nucleophilic properties as a factor in the formation of antifriction and hydrophobic properties of surface-modified metals with ammonium and organosilicon compounds

Stabilisation of the functional properties of dispersed and compact metals, as well as the regulation of their reactivity, improvement of water-repellent, antifriction and anti-corrosion properties by creating the protective films on the surface is an urgent problem in relation to obtaining new materials. Previously, research conducted at REC “Nanotechnology” of the St. Petersburg Mining University proved that chemisorption of ethylhydridesiloxane vapours together with surfactants based on quaternary ammonium compounds has a beneficial effect on the water-repellent properties of metals. In order to obtain the physicochemical mechanism of the hydrophobisation of the surface of modified dispersed metals for the firsttime, the study of the electrophilic-nucleophilic properties of the active substances of the surface modifiers of metals was carried out using the methods of quantum-chemical modelling using HyperChem software package. The dipole moment, energy of the highest occupied and the lowest unoccupied molecular orbitals, electrophilic-nucleophilic properties were determined. The series of enhancement of ucleophilic/electrophilic properties and dipole moment for modifiers were obtained. The donor-acceptor properties, the differences in the characteristics of the molecules of alkamon, triamon, and hydrophobic silicone organic liquid were quantitatively and qualitatively established. The regularities of the formation of hydrophobic and antifriction properties in the composition of industrial oil I-20-surface-modified metal with various electrophilic-nucleophilic properties of the applied substances

Strengthened adsorption and corrosion inhibition of new single imidazole-type ionic liquid molecules to copper surface in sulfuric acid solution by molecular aggregation

This study proposes to use molecular aggregation method of organic ionic liquid molecules (OILMs) to intensify adsorption and corrosion inhibition to copper surface in sulfuric acid solution. Three new single imidazole-type OILMs including long carbon chain were synthesized, which were characterized by different methods such as nuclear magnetic resonance (NMR) and elemental analysis. The results suggest that the OILMs could process regular molecular assembly in sulfuric acid solution. The formed OILMs aggregates have been shown dependence on the OILMs concentrations and aggregation time. The chemistry adsorption of the OILMs aggregates on copper surface was demonstrated by various means including attenuated total reflection infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and spectroscopic ellipsometry and contacting angles, and atomic force microscopy (AFM) as well as scanning electron microscopy (SEM) imaging. Thus, the hydrophobic adsorption layers of the OILMs aggregates were yielded on copper surface. The electrochemistry survey suggests that the OILMs aggregates present nice corrosion resistance effect to copper in sulfuric acid solution (the maximal corrosion inhibition efficiency, >93%). The results were further understood by the theoretical simulation computation.

Effects of Layering and Supporting Substrate on Liquid Slip at the Single-Layer Graphene Interface

Understanding modulation of liquid molecule slippage along graphene surfaces is crucial for many promising applications of two-dimensional materials, such as in sensors, nanofluidic devices, and biological systems. Here, we use force measurements by atomic force microscopy (AFM) to directly measure hydrodynamic, solvation, and frictional forces along the graphene plane in seven liquids. The results show that the greater slip lengths correlate with the interfacial ordering of the liquid molecules, which suggests that the ordering of the liquid forming multiple layers promotes slip. This phenomenon appears to be more relevant than solely the wetting behavior of graphene or the solid-liquid interaction energy, as traditionally assumed. Furthermore, the slip boundary condition of the liquids along the graphene plane is sensitive to the substrate underneath graphene, indicating that the underlying substrate affects graphene's interaction with the liquid molecules. Because interfacial slip can have prominent consequences on the pressure drop, on electrical and diffusive transport through nanochannels, and on lubrication, this work can inspire innovation in many applications through the modulation of the substrate underneath graphene and of the interfacial ordering of the liquid.

Development of an Infinite Dilution Activity Coefficient Prediction Model for Organic Solutes in Ionic Liquids with Modified Partial Equalization Orbital Electronegativity Method Derived Descriptors.

The objective of this study was to develop a robust prediction model for the infinite dilution activity coefficients (γ∞) of organic molecules in diverse ionic liquid (IL) solvents. Electrostatic, hydrogen bond, polarizability, molecular structure, and temperature terms were used in model development. A feed-forward model based on artificial neural networks was developed with 34,754 experimental activity coefficients, a combination of 195 IL solvents (88 cations and 38 anions), and 147 organic solutes at a temperature range of 298 to 408 K. The root mean squared error (RMSE) of the training set and test set was 0.219 and 0.235, respectively. The R2 of the training set and the test set was 0.984 and 0.981, respectively. The applicability domain was determined through a Williams plot, which implied that water and halogenated compounds were outside of the applicability domain. The robustness test shows that the developed model is robust. The web server supports using the developed prediction model and is freely available at https://preadmet.bmdrc.kr/activitycoefficient_mainpage/prediction/.

An Overview on Atomization and Its Drug Delivery and Biomedical Applications

Atomization is an intricate operation involving unstable and complex networks with rupture and fusion of liquid molecules. There are diverse details that typify the spray formation, which are the technique and configuration of the atomization process, dimension and structure of the nozzle, experimental parameters, etc. Ultimately, the process generates fine sprays from the bulk of a liquid. Some examples of atomization that we come across in our day-to-day life are antiperspirant or hair spray, shower head, garden sprinkler, or cologne mist. In this review paper we are briefly discussing the theoretical steps taking place in an atomization technique. The instabilities of the jet and sheet are explained to understand the underlying theory that breaks the jet or sheet into droplets. Different types of atomization processes based on the energy sources are also summarized to give an idea about the advantages and disadvantages of these techniques. We are also discussing the various biomedical applications of the electrohydrodynamic atomization and its potential to use as a drug delivery system. In short, this paper is trying to demonstrate the diverse applications of atomization to show its potency as a user friendly and cost-effective technique for various purposes.

Influence of the drying method on the structure of aluminum oxide capillary-porous nanomembranes

Porosity characteristics are widely used to assess the internal structure of nanomembranes. The membrane was considered complex in the analysis of the structure. The membrane was presented in a simplified way as a system interacting with a dispersion medium, for example, water. A physicochemical model of the membrane has been proposed, which allows one to study the logical and structural similarity between systems, the properties of which are known, with similar systems, but with unknown properties. We have chosen a simple mechanical model of a membrane permeable to liquid and gas molecules. Permeability was determined by the characteristics of the porosity, shape, and size of the pores.

Slip length of branched hydrocarbon oils confined between iron surfaces

In this paper, the slip length of branched hydrocarbon molecules, i.e., polyalphaolefin oils, under shear in a gap between iron surfaces were investigated utilizing large-scale Molecular Dynamics (MD) simulation. The results showed the expected singularity for the slip length with variation gap height. For large gap height, h→∞, the slip length approaches a constant asymptote λ→λ∞. This study indicated that as the number of branches of the liquid molecule raise, the slip length λ→λ∞ as well as viscosity increases. For given apparent shear rate, the friction force increased with increasing temperature due to the reduction of wall slip. MD Simulations demonstrate that the slip length of the polyalphaolefin-iron system increase by decreasing the liquid temperature, indicating an Arrhenius process.

Scalable Fabrication of Kevlar/Ti3C2Tx MXene Intelligent Wearable Fabrics with Multiple Sensory Capabilities.

Fiber-based wearable electronics are highly desirable for wearable devices that are expected to be lightweight, easily prepared, durable, flexible, washable, and conformable. However, developing fiber-based fabric electronics to simulate human perceptual systems or even transcend the sensory capabilities of natural creatures is still a pivotal challenge. Herein, we present a Kevlar/MXene (KM) intelligent wearable fabric with multiple sensory capabilities using an ingenious strategy of continuous wet-spinning. The KM fibers can be washed, knitted, sewed, and fabricated into smart KM fabric sensory systems. An intelligent KM sensory mask is prepared to monitor human breathing in time to detect respiratory problems with high accuracy and portability. It provides an important reference for judging diseases and achieving remote diagnosis. Additionally, a smart temperature-responsive sensory glove is developed to help people make proper behavioral prejudgments and prevent potential injuries by sensing surrounding hazards beforehand. Moreover, this sensory system allows soft robotics to make a rough identification about the basic properties of unknown liquid molecules. Overall, by the virtue of the ultrafast responsiveness (90 ms), resilience (110 ms), and ultrasensitive capability in pressure responding, this KM sensory system offers a gentle approach for wireless detection in information encryption, transmission, and preservation by touching the sensory system with variable pressing time on the basis of the International Morse code principles, establishing a competitive and promising candidate for next generation wearable flexible fabric electronics.

Construction of vitrinite molecular structures based on 13C NMR and FT-IR analysis: Fundamental insight into coal thermoplastic properties

Attempts were made to construct the molecular structures of vitrinite samples from four bituminous with different ranks and to investigate the correlation of molecular structures to thermoplastic properties of vitrinite by using a number of advanced analytical techniques combined with theoretical methods. The Gieseler plastometry and caking index showed that the Ewirgol vitrinite had a high fluidity (MF = 17675 ppm), wide plastic range (ΔT = 105.1 °C) and good caking properties (G = 99.32). Various analytical technique, e.g. Solid-state 13C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction analysis and Raman spectroscopy, provided comprehensive structural information for establishing molecular models of vitrinite samples with Density Functional Theory. These molecular models showed that the Ewirgol vitrinite had more cyclic aliphatic structures that contribute significantly to the fluidity development and caking properties. These cyclic aliphatic structures could be precursors of the aromatic rings in liquid molecules during coking and provide transferable hydrogens that saturate the free radicals in the thermoplastic range. The cyclic aliphatic structures may facilitate the formation of such molecular structures with an appropriate molecule size that maintains the mobile phase in the thermoplastic range to develop fluidity.

Optical Feedback for Sensitivity Enhancement in Direct Raman Detection of Liquids

Detection of low-concentration molecules in liquids has been a challenge in sensing technologies. Raman spectroscopy is an effective approach for trace detection, which is in fact a “volume-excitation” and “volume-collection” technique in the analysis of liquid samples. However, for the commonly employed one-pass excitation and back-scattering detection scheme, a large portion of both the excitation laser energy and the Raman-scattering light energy is wasted without efficient reuse or collection. In this consideration, we demonstrate a broadband optical feedback scheme by a curved high-reflection mirror for both the excitation and the Raman-scattering light, so that the excitation and the forward-propagating Raman signal can be back-reflected and collected with a high efficiency. Using the “F+2f” design, where F and f are the focal lengths of the focusing lens and curved reflection mirror, respectively, we were able to not only produce two focuses of the excitation laser beam but also extend the Raman interaction by a doubled distance. For the detection of pure ethanol molecules and the R6G molecules in water with a concentration of 10−3 M, the Raman signal was enhanced by a factor of about 5.6. The optical feedback scheme and discovered optical mechanisms supply effective improvements to the Raman spectroscopic measurements on liquid samples.

How wettability affects boiling heat transfer: A three-dimensional analysis with surface potential energy

How surface wettability affects boiling heat transfer is still a challenging problem at nanoscale. In this work, a three-dimensional analysis of surface potential energy is used to address its relationship to surface wettability and nanoscale pool boiling characteristics of liquid molecules. It is found that the major reason for the enhanced heat transfer by increasing the surface wettability is essentially the improvement of surface potential energy, of which the influence is summarized using logic order. Moreover, the nanoscale boiling of water on copper surfaces with various wettability is investigated, which reveals that the increase in surface wettability can improve the heat transfer coefficient and critical heat flux under high superheat conditions in both nano- and macroscale systems. Besides, the effects of surface potential energy on contact angle, Kapitza resistance, heat transfer coefficient, and critical heat flux are analyzed systematically to demonstrate their relationships. A nondimensional analysis is finally implemented to correlate the normalized surface potential energy (P), the Nusselt number (Nu), and the normalized critical heat flux (J): Nu = 0.081P0.34, J = 0.827P0.50 (P < 2.387) and J = 1.221P0.05 (P > 2.387). This work provides insights into the enhancement mechanisms for the phase-change heat transfer of liquid molecules over surfaces with different wettability.