Decrease In Free Energy Research Articles

Virtual screening of two-dimensional selenides and transition metal doped SnSe for lithium-sulfur batteries: A first-principles study

Two-dimensional (2D) metal chalcogenides are promising sulfur host materials for lithium-sulfur (Li-S) battery owing to their abundance on earth and unique physicochemical properties. Although 2D metal sulfides have been investigated for applications in Li-S battery, selenides with higher conductivity than sulfides are scarcely studied. Herein, focusing on finding the optimal 2D selenide as sulfur host of Li-S battery, for the first time, a series of 2D selenides were screened in terms of adsorption capacity and catalytic effect on conversion reactions for lithium polysulfides (LiPSs) using first-principles approach. Among them, SnSe is the best performer with the LiPSs/S8 adsorption energies of −0.77 to −2.31 eV and lowers the free energy of overall S8 reduction reaction (SRR) by 2.31 eV. For further improving the performance of 2D SnSe, eleven transition-metal doped 2D SnSe (TM-SnSe) were constructed and show enhanced anchoring capability and catalytic effect, among which Ti-SnSe stands out with adsorption energies of −2.09 to −4.01 eV and SRR free energy decrease of 3.27 eV. The electronic and structural analyses unveil that the considerable interaction enhancement between Ti-SnSe and LiPSs/S8 comes from strong Ti–S bond and enhanced Sn–S bond. Combining with the experimentally mature synthesis of 2D SnSe and doping strategy, Ti-SnSe is of great possibility to be obtained and achieve great improvement for Li-S battery.

Thermodynamic relations and ro-vibrational energy levels of the improved Pöschl–Teller oscillator for diatomic molecules

In this paper, the formalism of improved quantization rule is used to obtain analytical expression for bound state ro-vibrational energies of the improved Pöschl–Teller oscillator (IPTO). In modeling the centrifugal term of the effective potential, a Pekeris-like approximation scheme is used. Expression for analytical normalized eigenfunctions is obtained by ansatz solution technique. The equation obtained for ro-vibrational energy is then used to derive relations for some important thermodynamic functions for the IPTO; these include ro-vibrational: partition function, Helmholtz free energy, mean energy, entropy and specific heat capacity. Using the spectroscopic data of RbH (X1Σ+) diatomic molecule, pure vibrational state energies for the IPTO are calculated. The results obtained are in good agreement with experimental Rydberg–Klein–Rees data and are better than energies of the RbH (X1Σ+) diatomic molecule obtained via improved generalized Pöschl–Teller potential. Studies have also shown that the ro-vibrational partition function increases monotonically with increase in either temperature (T) or upper bound vibrational quantum number (λ). On the other hand, increase in any of T or λ results in monotonic decrease in ro-vibrational Helmholtz free energy of the system.

Development of a novel dual-bioinspired method for synthesis of a hydrophobic/hydrophilic polyethersulfone coated membrane for membrane distillation

This study presented a novel method for the surface modification of a hydrophilic polyethersulfone (PES) membrane via dip-coating. The performance of the new membrane was investigated in a membrane distillation process. The surface free energy (SFE) of the modified PES was studied by the Owens–Wendt method. A significant decrease of surface free energy from 36.1 mN/m to 16.4 mN/m was observed after modifying the membrane surface with fluoro-organothiol (1H, 1H, 2H, 2H-perfluorodecanethiol). The water contact angle of the membrane increased from 66° for PES to 115° for surface-modified membrane. This remarkable increase suggests a successful switch from hydrophilicity to hydrophobicity owing to the creation of hierarchical submicro/nanostructures on the surface of PES. This structure was achieved by depositing polydopamine and silver nanoparticles, followed by lowering the surface free energy by fluoro-organothiol treatment. The performance of the modified membranes was evaluated through a direct contact membrane (DCMD) process in the presence of anionic and non-ionic surfactants and high salt concentrations (4.5 wt%). The membranes reached a high and stable flux of approximately 39.37 kg/m2h after surface modification. Besides, the newly engineered membranes had excellent stability during long-term operation, showing a salt rejection rate of 99.80% after 36-h.

Mechanistic insights into and modeling the effects of relative humidity on low-concentration VOCs adsorption on hyper-cross-linked polymeric resin by inverse gas chromatography

Water vapor is very common in contaminated streams, which has a great influence on the adsorption of low-concentration volatile organic compounds (VOCs) due to the competition between water and VOCs. Understanding adsorption mechanisms and predicting adsorption of VOCs under different relative humidity (RH) are of great importance to design effective adsorption unit. In this study, we comprehensively investigated the effects of RH on the surface properties of hyper-cross-linked polymeric resin (HPR) and adsorption of 18 VOCs at low concentration on HPR under five levels of RH using inverse gas chromatography (IGC). Further, a promising RH-dependent poly-parameter linear free energy relationships (PP-LFERs) model was developed. It was found that water vapor caused the decrease of surface free energy (γst) of HPR due to the occupation of active sites by water molecules, resulting in the decrease of adsorption partition coefficients (K). Moreover, the γst could accurately quantify the effects of RH on the surface properties of HPR. Therefore, the RH-dependent PP-LFERs model was established by correlating RH and γst. The developed model overcame the limited predictive ability of existing models only under a specific RH level, and excellently predicted the lnK values of VOCs (R2 = 0.944, RMSEt = 0.36 and RMSEv = 0.47) under various RH.

Realization of synergistic enhancement for fracture strength and ductility by adding TiC particles in wire and arc additive manufacturing 2219 aluminium alloy

TiC reinforced Al-matrix composites were fabricated by wire and arc additive manufacturing (WAAM) method. The effects of TiC content on the evolution of grain boundary structure, phase transformation, grains distribution, interface mismatch, and mechanical properties of the WAAM-deposited 2219 Al–Cu alloys were investigated. The columnar grains in the inner-layer zone were transformed to equiaxed grains by the addition of TiC particles, which eventually induced the decrease of free energy for the Al-matrix, promoting an opportunity for nuclei to grow on the TiC substrate. TiC particles played an important role in generating the nucleation supercooling (ΔTns, 3.8 °C), multi-site heterogeneous nucleation with a lower value of ΔTns inhibited the constitutional supercooling (ΔTcs) caused by segregation of Cu. The degree of grain boundary segregation was greatly weakened, and the α-Al+θ-CuAl2 phase was semi-coherent with the matrix at the grain boundary, i.e. [1–31]Al2Cu//[0–11]Al, (211)Al2Cu//(100)Al. The fine spot-like phase possessed a strong interfacial bonding with the Al-matrix. The Al2Cu and TiC possessed a coherent interface with crystal orientation relations, i.e. [00–1]TiC//[01-1]Al2Cu, (110)TiC//(100)Al2Cu. Besides that, the fine spot-like phases and the well-dispersed TiC particles within the grains promoted the formation of dislocations. Therefore, the strength and toughness of the deposited 2219 alloy were improved synergistically. Eventually, the deposited sample exhibited a tensile strength around 384 MPa, and the elongation was up to 18.3%.

Effect of Silver Clusters Deposition on Wettability and Optical Properties of Diamond-like Carbon Films

In this study, the effect of silver clusters deposition was investigated on optical, wettability and surface properties of diamond-like carbon (DLC) films. Silver clusters and DLC films were deposited on Ni-Cu (70.4-29.6;W/W) alloy substrates by ion beam sputtering deposition (IBSD) technique. Optical and structural properties were measured using UV-visible spectroscopy and Raman spectroscopy, respectively. The wettability and surface free energy of films were determined by the contact angle (CA) measurements. Raman spectra of DLC thin film with 121±6nm thickness without accumulated Ag showed that the size of the graphite crystallites with sp 2 bands (La) was 3.36A by the ID/IG ratio equal to 0.062 with large optical band gap equal 3eV extracted from Tauc relation. The results of the deposition Ag in the various ion beam energy between 0.6 to 2keV showed the Ag clusters were accumulated uniformity on the surface of DLC films at 0.9keV. The volume percentage of silver clusters was varied from 5.0±2.01 to 16.3±1.4. The variation was caused by controlling the screen voltage and the deposition time. The CA of the deposited films increases from 79°±2 to 95°±2 as well as the reflection values in the visible and near-infrared region due to the increase in the Ag concentration in the surface of DLC films; while the surface free energy decrease from 86±1 to 66±2mJ/m2 and the optical transmittance is almost constant. Our results demonstrate that the deposition of silver particles on DLC films is potentially useful for biomedical applications having good hydrophobic characteristics without causing a destructive effect on the optical properties of DLC films.

Collective Solvation and Transport at Tetrahydrofuran-Silica Interfaces for Separation of Aromatic Compounds: Insight from Molecular Dynamics Simulations.

We have performed umbrella sampling molecular dynamics simulations to study the separation mechanism of aromatic compounds at the tetrahydrofuran (THF)-methanol-silica interface by liquid chromatography. Solute molecules with different polarities (naphthol and naphthalene) are selected as representative aromatic compounds. For the polar solute (naphthol), the free energy profile shows a deep minimum near the THF-silica interface, suggesting strong interactions with the polar surface. When methanol is added to the interface, there is a sharp increase in naphthol's free energy minimum, and the corresponding diffusion dynamics also undergoes a dramatic change. These findings explain the fast separation mechanism in recent experiments of separating fused ring compounds in asphaltenes with liquid chromatography. Further solvation structure and orientation analysis suggest that apolar and polar solutes may find their own comfort zones several angstroms away from the interface, and their phenyl ring's orientations would undergo a parallel-to-perpendicular transition as the solute molecule moves away from the surface. Extending our simulation studies to systems with different solute concentrations reveals that there is a decrease in the adsorption free energy accompanied by enhanced surface diffusion as the solute concentration increases, which is related to the crowding in the interfacial layers. Our simulation analysis gives a detailed microscopic description of solute solvation and transport at the THF-silica chromatography interface and will be helpful for improving separation protocols in future applications.

Entropy and enthalpy changes during adsorption and displacement of shale gas

Shale gas is a major component of the hydrocarbon economy, and there are abundant studies in related exploration and exploitation fields using simulations and experiments. In this paper, the kinetic processes of adsorption and displacement during shale gas exploitation are analyzed using enthalpy-driven and entropy-driven processes with molecular dynamics simulations and statistical mechanics analyses. First, the changes in symmetry of CH4 and CO2 adsorbed on the graphene surface are analyzed. The adsorption process is a spontaneous process, where the Gibbs free energy decreases. During this process, the gas molecular entropy and the enthalpy of the system decrease, which indicates an enthalpy-driven process. The changes in entropy and enthalpy of various gas molecules (CH4, CO2, N2, and H2O) during the adsorption process are obtained. Through comparing the entropy and enthalpy changes before and after the displacement of CH4 by the different displacement media (CO2, N2, and H2O). The CO2-injected displacement of CH4 is driven by both enthalpy and entropy, and the N2-injected displacement of CH4 is driven by entropy. However, H2O-injected displacement of CH4 is not a spontaneous process. It plays a certain displacement role by reducing the partial pressure of CH4. To clarify the detailed spontaneous processes, the entropy change and exothermic processes during the supercritical fluid displacement of shale gas are discussed; then, the differences in displacement efficiency of different supercritical fluids are explained. This study is useful for understanding the kinetics mechanism of adsorption and displacement of shale gas.

The freezing behavior of aqueous n-alcohol nanodroplets.

We generate water-rich aerosols containing 1-propanol and 1-pentanol in a supersonic nozzle to study the effects of these solutes on the freezing behavior of water. Condensation and freezing are characterized by two complementary techniques, pressure trace measurements and Fourier Transform Infrared spectroscopy. When 1-pentanol and 1-propanol are present, condensation occurs at higher temperatures because particle formation from the vapor phase is enhanced by the decrease in interfacial free energy of mixed aqueous-alcohol critical clusters relative to those of pure water. FTIR results suggest that when ∼6 nm radius droplets freeze, the tetrahedral structure of the ice is well preserved up to an overall alcohol mole fraction of 0.031 for 1-propanol and 0.043 for 1-pentanol. In this concentration range, the ice nucleation temperature decreases continuously with increasing 1-propanol concentration, whereas the onset of freezing is not significantly perturbed by 1-pentanol up to a mole fraction of 0.03. Furthermore, once freezing starts the ice nucleation rates in the aqueous-alcohol droplets are very close to those for pure water. In contrast, at the highest mole fractions of either alcohol it is not clear whether droplets freeze to form crystalline ice since the final state of the particles cannot be adequately characterized with the available experimental techniques.

Engineering carbon nanotubes enhanced hydrophobic membranes with high performance in membrane distillation by spray coating

The commonly used commercial hydrophobic membranes are facing great challenges in wetting and low permeation when used in membrane distillation (MD) because of the limited materials and structures. To address these problems, we herein fabricated a kind of carbon nanotubes (CNTs) enhanced membrane with high flux and stable performance in membrane distillation, where a porous hydrophobic network of multi-walled carbon nanotubes (MWCNTs) was spray-coated onto the commercial flat-sheet hydrophobic membrane surface. Then, we systematically investigated the impact of the CNTs loading on the substrate surface properties, membrane structures and MD performance (flux and rejection), and experimentally illustrated the role of CNTs towards improving MD performance. Results illustrate that there is an optimal match of the CNTs spray amount with the substrate pore size and the substrate materials to achieve the maximum specific surface area of membrane, and thus the maximum flux and salt rejection of the resultant CNTs-enhanced membrane, which is governed by the interfacial energy of the CNTs and the substrate, and thus the CNTs packing density. Results find that the CNTs packing density decreases with the decrease of the substrate free surface energy, and the loosest CNTs packing is formed on the polytetrafluoroethylene (PTFE) membrane with the lowest free surface energy. Under the optimized conditions, the CNTs enhanced PTFE membrane exhibited salt rejection of >99.9% and water flux of 33.2 LMH in MD, which was three times as high as that of the pristine PTFE membrane under the temperature difference of 40 °C between hot and cold streams when operated in direct contact membrane distillation. Our research here provides an efficient method to enhance the permeation and stability of commercial membranes by spray-coating CNTs and also supplies some insights on the design of next-generation MD membranes.

Effects of nano-pore and macromolecule structure of coal samples on energy parameters variation during methane adsorption under different temperature and pressure

Research on methane adsorption in coal reservoirs by combining adsorption energy variation with molecular structure helps to explain the micro adsorption mechanism of methane. According to experimental data obtained from methane isothermal adsorption at different temperatures (20, 30 and 40 degrees centigrade) and pressure (0 ~ 10 MPa), effects of temperature and pressure on the energy parameters (adsorption potential, adsorption space, surface free energy and isosteric heat of adsorption) of middle and high rank coal samples were discussed from the angles of adsorption kinetics and thermodynamics. Moreover, pore and macromolecular structure of all the samples were elucidated by employing low temperature liquid nitrogen, carbon dioxide adsorption and infrared spectroscopy. Then, relationship between micro-pore structure, chemical structure parameters and adsorption energy variation were discussed. The following results has been achieved. 1) As adsorption pressure increases, reduction rate of surface free energy grows rapidly at the early period of lower pressure stage (0 ~ 8 MPa), then it becomes less than that of higher pressure stage (8 ~ 10 MPa). At the same adsorption pressure, reduction value rate of surface free energy decreases as coal rank increase. 2) Increasing temperature causes the decrease of adsorption capacity (VL and PL), and the sensitivity of temperature to adsorption capacity of high rank samples is stronger than that of middle rank samples. As Ro, max increases, initial isosteric heat of adsorption gradually increases. 3) In contrast to meso-macropore, micro-pore is critical affecting adsorption capacity. Larger specific surface area and adsorption potential of micro-pore results in a decrease in the surface free energy. 4) When Ro, max is less than 2.5%, the graphitization degree of aromatic increase linearly, and the length of the aliphatic chain reaches the minimum value. After that, macromolecule parameters varies smoothly. Then, functional groups variation affects the micro-pore structure evolution, whereas has a weak effect on the meso-macropore structure. Moreover, as apparent aromaticity (fa) increases, maximum surface free energy of coal sample increases linearly and the initial isosteric heat of adsorption increases exponentially, respectively. Above all, gas adsorption energy variation affects methane adsorption capacity, then it is also influenced by the micro-pore and internal chemical structure.

Solvent-free functionalization of graphene oxide powder and paper with aminobenzo-crown ethers and complexation with alkali metal cations

Graphene oxide powder and graphene oxide paper were covalently functionalized with the 4′-aminobenzo-15-crown-5 (AB15C5) and 4′-aminobenzo-18-crown-6 (AB18C6) ethers by a solvent-free gas-phase treatment. Then, we attempted the complexation with potassium and sodium cations. A comparative characterization in the functionalized graphene oxide structures was carried out using Fourier-transform infrared (FTIR), Raman and X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermal analysis (TGA and DTA, respectively), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The wettability of graphene oxide paper (GOP) samples was analyzed by measuring the contact angle. The degree of covalent functionalization in GO powder with aminobenzo-crown ethers was estimated at 27% (AB15C5) and 19% (AB18C6). The amount of organics attached to GOP samples was approximately 7%. After the interaction with potassium and sodium cations, the functionalized GOP samples showed an increase in the contact angle, followed by a decrease in surface free energy. The complexation with alkali metal cations suggests an uptake of about 3%. However, the cation selectivity for alkali metal ions was dependent on the ions' radius. Surface free energy measurements suggest that complexation with potassium effectively takes place when using AB18C6.

On the Role of Entropy in the Stabilization of α-Helices.

Protein folding evolves by exploring the conformational space with a subtle balance between enthalpy and entropy changes which eventually leads to a decrease of free energy upon reaching the folded structure. A complete understanding of this process requires, therefore, a deep insight into both contributions to free energy. In this work, we clarify the role of entropy in favoring the stabilization of folded structures in polyalanine peptides with up to 12 residues. We use a novel method referred to as K2V that allows us to obtain the potential-energy landscapes in terms of residue conformations extracted from molecular dynamics simulations at conformational equilibrium and yields folding thermodynamic magnitudes, which are in agreement with the experimental data available. Our results demonstrate that the folded structures of the larger polyalanine chains are stabilized with respect to the folded structures of the shorter chains by both an energetic contribution coming from the formation of the intramolecular hydrogen bonds and an entropic contribution coming from an increase of the entropy of the solvent with approximate weights of 60 and 40%, respectively, thus unveiling a key piece in the puzzle of protein folding. In addition, the ability of the K2V method to provide the enthalpic and entropic contributions for individual residues along the peptide chain makes it clear that the energetic and entropic stabilizations are basically governed by the nearest neighbor residue conformations, with the folding propensity being rationalized in terms of triads of residues.

A reaction density functional theory study of solvent effect in the nucleophilic addition reactions in aqueous solution

Whereas the proper choice of reaction solvent constitutes the cornerstone of the green solvent concept, solvent effects on chemical reactions are not mechanistically well understood due to the lack of feasible molecular models. Herein, by taking the case study of nucleophilic addition reaction in aqueous solution, we extend the proposed multiscale reaction density functional theory (RxDFT) method to investigate the intrinsic free energy profile and total free energy profile, and study the solvent effect on the activation and reaction free energy for the nucleophilic addition reactions of hydroxide anion with methanal and carbon dioxide in aqueous solution. The predictions of the free energy profile in aqueous solution for these two nucleophilic addition reactions from RxDFT have a satisfactory agreement with the results from the RISM and MD-FEP simulation. Meanwhile, the solvent effect is successfully addressed by examining the difference of the free energy profile between the gas phase and aqueous phase. In addition, we investigate the solvent effect on the reactions occurred near solid–liquid interfaces. It is shown that the activation free energy is significantly depressed when reaction takes place in the region within 10 Å distance to the substrate surface owing to the decrease of hydration free energy at the solid–liquid interface.

Design, characterization and in vitro evaluation of thin films enriched by tannic acid complexed by Fe(III) ions

Materials based on carbohydrate polymers may be used for biomedical application. However, materials based on natural polymers have weak physicochemical properties. Thereby, there is a challenge to improve their properties without initiation of toxicity. The alternative method compared to toxic chemical agents’ addition is the use of metal complexation method. In this study, chitosan/tannic acid mixtures modified by Fe(III) complexation are proposed and tested for potential applications as wound dressings. Thereby, surface properties, blood compatibility as well as platelet adhesion was tested. In addition, the periodontal ligament stromal cells compatibility studies were carried out. The results showed that the iron(III) addition to chitosan/tannic acid mixture improves properties due to a decrease in the surface free energy and exhibited a reduction in the hemolysis rate (below 5%). Moreover, cells cultured on the surface of films with Fe(III) showed higher metabolic activity. The current findings allow for the medical application of the proposed materials as wound dressings.

Impact of cigarette smoke on physical-chemical and molecular proprieties of human skin in an ex vivo model.

This is a study about the skin ageing exposome, focusing on the effect of cigarette smoke. Human living skin explants (HSE) were exposed to cigarette smoke (CS) of two cigarettes for 2hours using a custom-made exposure chamber, the Pollubox® . Effects on the surface physico-chemistry and molecular properties of the skin were analyzed and reported for the first time. To this end, transcriptomic study followed by immunohistochemistry, MDA (Malondialdehyde Dosage), and surface physio-chemistry data: surface free energy determination, TEWL (Trans Epidermal Water Loss), skin pH and FT-IR (Fourier Transform-Infrared) spectroscopy of the explant were collected from untreated and treated HSE. Results showed a decrease of the total surface free energy of the treated HSE. This decrease reflected higher interactions with polar compounds from the environment and consequently a decrease of the surface hydrophobicity. Additionally, an increase of TEWL and skin pH was observed after treatment. The transcriptomic analysis showed downregulation of mitochondrial genes (PON2-NDUFA4L2-ATP1A1-ALDH2-PRODH) combined with an increase of MDA in CS-treated HSE. CS-induced oxidation of lipids at HSE surface alters the skin barrier: interactions with polar products are enhanced and the lipid chain packing at the surface is modified. Consequently, skin permeability could increase which correlated with repression of CA9 and AQP1 genes. Beside activation of AHR-NRF2 pathway in CS-exposed HSE, our results suggested that mitochondrial functions were strongly impacted and oxidized lipids failed to be eliminated promoting skin barrier alteration. A mitophagy activity was suggested through the confirmation of PINK1 accumulation in the epidermis by immunostaining.

Effective Reinforcement of Melamine-functionalized WS2 Nanosheets in Epoxy Nanocomposites at Low Loading via Enhanced Interfacial Interaction

We present a two-dimensional tungsten disulfide (WS2)-based material as a reinforcement additive to produce thermally stable, mechanically strong, and light-weight epoxy (EP) composites. An aqueous melamine solution was used to exfoliate the bulk WS2 into nanosheets while simultaneously functionalizing them to obtain melamine-functionalized WS2 (N-WS2) nanosheets. These non-covalently functionalized N-WS2 nanosheets were used as toughening agents for epoxy composites. The contents of the N-WS2 nanosheets were maintained at below 1 wt%. The effect of functionalization on the interfacial properties of EP composites was investigated in terms of the interfacial interactions between the EP and the nanosheets. The results demonstrated that the surface free energy of EP composites increased significantly after the incorporation of N-WS2 nanosheets into the EP matrix and further increased with the increased loading of N-WS nanosheets up to a maximal value of 54.38 mJ-m2 for the composite containing 0.18 wt% N-WS2 nanosheets, suggesting a stronger interfacial interaction between the EP and N-WS2 nanosheets. A gradual decrease in the surface free energy of the EP composites was observed at higher loadings, which might be attributed to the aggregation of N-WS2 nanosheets within the matrix or excessive bonding of the sheets with one another rather than with the EP matrix due to their larger Van der Waals forces and their large surface area. The mechanical properties of the EP composites were analyzed and demonstrated 55%, 101%, 44%, and 15% improvements in the fracture toughness, fracture energy, flexural strength, and flexural modulus, respectively, for the composite containing 0.18 wt% N-WS2 nanosheets. Moreover, the composites displayed increased glass transition temperatures and better thermal stabilities.

Investigating the Applicability of Molecular Dynamics Simulation for Estimating the Wettability of Sandstone Hydrocarbon Formations.

One of the techniques to increase oil recovery from hydrocarbon reservoirs is the injection of low salinity water. It is shown that the injection of low salinity water changes the wettability of the rock. However, there are argumentative debates concerning low salinity water effect on changing the wettability of the oil/brine/rock system in the oil reservoirs. In this regard, molecular dynamics simulation (MDS) as a tool to simulate the phenomena at the molecular level has been used for more than a decade. In this study, the Zisman plot (presented by KRUSS Company) was simulated through MDS, and then, contact angle experiments for n-decane interactions on the Bentheimer substrate in the presence of different concentrations of sodium ions were conducted. MDS was then used to simulate experiments and understand the wettability trend based on free-energy calculations. Hereafter, a new model was developed in this study to correlate free energies with contact angles. The developed model predicted the experimental results with high accuracy (R2 ∼ 0.98). A direct relation was observed between free energy and water contact angle. In contrast, an inverse relation was noticed between the ion concentration and the contact angle such that an increase in the ion concentration resulted in a decrease in the contact angle and vice versa. In other terms, increasing brine ionic concentrations in the presence of n-decane is linked to a decrease in free energies and an increase in the wetting state of a sandstone. The comparison between the developed model’s predicted contact angles and experimental observations showed a maximum deviation of 14.32%, which is in satisfactory agreement to conclude that MDS can be used as a valuable and economical tool to understand the wettability alteration process.

Synthesis of a novel metal-organic nanocomposite film (MONF) with superior corrosion protection performance based on the biomimetic polydopamine (PDA)-based molecules and Sm2O3 particles on the steel surface

In recent years, the nanocomposite films have been utilized for the metals' corrosion resistance enhancement. In this research, an eco-friendly samarium (III) and bio-compatible polyodopamine-based biopolymer have been applied to mitigate the corrosion of steel through the construction of a hybrid film with effective anti-corrosion potency. For this purpose, the PDA micro/nano-particles were synthesized via two well-known self-polymerization and oxidant-facilitated methods. Then, they were introduced into the Sm (III)-based chemical modification bath, and the resulting solutions were sprayed on the steel surface continuously. The steel panels coated with samarium-oxide nanofilm, as well as the Sm-PDA composite coating, have shown excellent water-repellency performance. Results evidenced 34% enhancement in the water contact angle (CA) and a 74% decrease in surface free energy (γs). Also, the SEM/EDS, XRD, and FT-IR analyses results revealed that the great surface hydrophobicity characteristic of the Sm-PDA modified sample is because of the synergistic effect of the nano-roughness of the Sm-nano film and the micro-scale roughness of the PDA particles. In addition, the XRD and FT-IR analysis outcomes affirmed the development of the films composed of the samarium oxide and PDA on the treated steel surface. The EIS and polarization test results revealed that via the steel surface treatment by Sm-PDA film, the total resistance (Rt) and icorr values increased/decreased for 4-fold and 65%, respectively. The Rt of the steel sample subjected to 0.6 M NaCl solution for 96 h is about 1163 (Ω.cm2), while this value for the Sm-treated, Sm-PDAS, and Sm-PDAO samples was 2778, 2915 and 4735 (Ω.cm2), respectively. Overall, the results confirmed the high water-proof and superior anti-corrosion potency of the composite Sm-PDA film.

Thermodynamically consistent forward and reverse degrees of rate control in reversible reactions

The net rate of a composite reaction is the difference between the forward and reverse reaction rates, which are kinetically distinct despite sharing elementary reaction steps and therefore have different rate-controlling transition states and species. Thus, degrees of rate control defined to identify rate-controlling transition states and species for the net rate confound contributions from the forward and reverse reactions. Herein, the forward and reverse degrees of rate control are defined to independently quantify the extent that species and transition states control the forward and reverse rates in reversible reactions. These degrees of rate control are defined as the relative change in the forward and reverse reaction rates per kBT decrease in the standard-state molecular free energies of transition states and species, and they are related to experimentally measurable quantities such as steady-state fractional coverages, reaction orders, and energies and entropies of activation of the forward and reverse reaction rates. The forward/reverse degrees of rate control represent stoichiometric coefficients for species and transition states in an equilibrium between the initial states and transition states of the apparent rate-controlling steps of forward and reverse overall reactions. At equilibrium, the apparent transition states for the forward reaction and reverse reaction converge, and thus the forward and reverse rate-controlling steps combine to form a single apparent rate-controlling step. This apparent rate-controlling step is comprised of an apparent initial state, transition state, and final state, where the apparent final state of the forward reaction is the apparent initial state of the reverse reaction. The apparent rate-controlling step behaves identically to an elementary step reaction at equilibrium with a pseudo-mass-action rate function given by the transition-state-theory (TST) form rate function (Foley and Bhan, 2020) with a stoichiometric number equal to the affinity-averaged stoichiometric number, σ¯. The ratio of the forward and reverse TST-form rate functions is identical to the overall thermodynamic equilibrium relation, consistent with the principles of microscopic reversibility and detailed balance at equilibrium.