Coulomb Force Research Articles

Contact ion-pair SN2 reactions activated by Lewis Base Phase transfer catalysts

We present experimental probes of contact ion-pair (CIP) SN2 reactions for simplest prototype systems by 19F-NMR spectroscopy. This study provides crucial evidences for the reactions of CIP metal salts facilitated by Lewis base phase transfer catalysts (PTCs) [2,2,2]-cryptand, 18-crown-6, pentaethylene glycols (pentaEGs) and BINOL–based pentaEG. The 19F-NMR spectra of MF (M = K, Cs) ion-pairs in various solvents are used as fingerprinting tools to identify the CIP CsF/PTC/substrate complexes in SN2 reactions. Examination of the prototype reactions demonstrates that the novel CIP mechanism, which is in sharp contrast to the conventional perspectives, may account for the observed phenomenal efficiency of the SN2 processes using the alkali metal salts under the influence of various PTCs. In this extremely efficient and selective protocol of wide applicability, the CIP MF is activated by the Lewis base PTCs acting on the counter-cation M+ to drastically mitigate the latter’s retarding Coulomb forces on the adjacent nucleophile F-, with or without the participation of hydrogen bonds.

Unraveling Ofloxacin Behavior in Aqueous Environments: Molecular Dynamics of Colloidal Formation and Surface Adsorption Mechanisms.

Ofloxacin, a commonly prescribed antibiotic, raises serious environmental concerns due to its persistence in aquatic systems. This study offers new insights into the environmental behavior of ofloxacin and its interactions with carbon-based adsorbents with the aim of enhancing our understanding of its removal mechanisms via adsorption processes. Using a comprehensive computational approach, we analyzed the speciation, pKa values, and solubility of ofloxacin across various pH conditions, accounting for all four microspecies, including the often-overlooked neutral form. Our findings indicate that clustering of ofloxacin in water is influenced not only by solubility but also by electrostatic repulsion, dipole creation, and π-π interactions. At extreme pH levels, clustering is primarily driven by Coulombic forces and strong π-π interactions between different ofloxacin molecules. Density functional theory (DFT) was employed to optimize the molecular structures, and molecular dynamics (MD) simulations explored interactions among ofloxacin, water, and carbon surfaces. Hybrid Reverse Monte Carlo (HRMC) simulations were used to determine the disordered structure of an activated carbon cloth (ACC), specifically, KIP1200 (Dacarb company, France), for use in MD simulations. KIP1200 contains a small amount of oxygen (less than 2%), which supports our assumption of a predominantly carbon-based structure. Surface interactions were found to vary significantly depending on the ofloxacin form. The neutral form exhibited strong π-π interactions with flat surfaces, whereas the zwitterionic form displayed a greater affinity for curved surfaces. On KIP1200, adsorption was pH-dependent: acidic conditions enhanced adsorption due to reduced repulsion, while adsorption decreased under basic conditions. The aromatic rings in ofloxacin, combined with the high electronegativity of its fluorine atoms, played a critical role in facilitating adsorption through π-π interactions. These results deepen our understanding of ofloxacin microspecies, colloid formation, and adsorption mechanisms under diverse conditions.

Pressure-Dependent Nonlinearities of a Compact Hydropneumatic Strut with Integrated Gas–Oil Chamber

<div>Hydropneumatic Struts (HPS) are widely implemented in automobile, aerospace, and construction industries, mainly for the purpose of vibration and shock absorption. The HPS design with integrated gas–oil chamber is relatively more compact and robust, while mixing gas and oil inside the HPS generates gas–oil emulsion and more nonlinearities. This study formulated a nonlinear analytical model of the compact HPS with gas–oil emulsion, considering the real gas law and pressure-dependent LuGre friction model. The polytropic version of the van der Waals (vdW) method for real gas is applied to represent the thermodynamic behavior of nitrogen. The experimental data were collected at a near temperature of 30°C with three charging pressures under excitations in the frequency range of 0.5–6 Hz, considering two flow connection configurations between chambers as one- and two-bleed orifice. The nonlinear behavior of the gas volume fraction of the emulsion was identified based on peak strut velocity and charge pressure. Discharge coefficients of bleed and check valves were determined as a function of the instantaneous pressure difference between chambers. The parameters of the pressure-dependent LuGre model, such as the stiction force and Coulomb force apart from stiffness and damping coefficient of bristle deflection, were also investigated considering the effect of pressure variation. Compared to the generally used ideal gas and models, the proposed model considerably improved the prediction accuracy of the total force and pressures of HPS, with normalized root-mean-square deviations of about 8%.</div>

Ultrahigh piezoelectric performances of (K,Na)NbO3 based ceramics enabled by structural flexibility and grain orientation

(K,Na)NbO3-based ceramics are deemed among the most promising lead-free piezoelectric materials, though their overall piezoelectric performance still lags behind the mainstream lead-containing counterparts. Here, we achieve an ultrahigh piezoelectric charge coefficient d33 ∼ 807 pC·N−1, along with a high longitudinal electromechanical coupling factor (k33 ∼ 88%) and Curie temperature (Tc ∼ 245 °C) in the (K,Na)(Nb1-xSbx)O3-Bi0.5Na0.5ZrO3-BiFeO3 (KNN-xSb) system through structural flexibility and grain orientation strategies. Phenomenological models, phase field simulations and high-angle annular dark-field scanning transmission electron microscopy reveal that the structural flexibility originates from the high Coulomb force between K+/Na+ ions and Sb ions in the KNN-xSb system, while the grain orientation promotes the displacement of B-site cations leveraging the engineered domain configuration. As a result of its excellent comprehensive piezoelectric properties, the textured KNN-5Sb/epoxy 1-3 piezoelectric composite is found to possess a broader bandwidth BW = 60% and higher amplitude output voltage than commercial PZT-5 and other KNN counterparts. These findings suggest that the textured KNN-5Sb ceramics could potentially replace current lead-based piezoceramics in transducer applications.

Molecular Dynamics Study of Polyacrylamide and Polysaccharide-Derived Flocculants Adsorption on Mg(OH)2 Surfaces at pH 11.

Brucite (Mg(OH)2) is a typical precipitate in the mining industry that adversely affects processes such as flotation and thickening. Gaining insights into the physicochemical properties of this mineral is critical for developing strategies to mitigate these challenges and improve operational efficiency. Additionally, incorporating natural-origin polymers aligns with the shift toward more sustainable mining practices. In this study, molecular dynamics simulations were employed to investigate the interaction of brucite with polysaccharides such as cellulose, guar gum, and alginate and to compare these with conventional polymers, including polyacrylamide, hydrolyzed polyacrylamide, and polyacrylic acid, under conditions of pH 11 in low-salinity water. The methodology enhanced adsorption sampling by incorporating additional temporary interactions between the polymer and the brucite surface. The results reveal that neutral polymers exhibit stronger and more stable interactions with brucite compared to charged polymers, which is consistent with the neutral nature of brucite under the studied conditions. Van der Waals forces predominantly govern the adsorption of polysaccharides, while Coulombic forces primarily drive interactions involving polyacrylamides. These findings provide valuable insights into the molecular mechanisms of polymer-brucite interactions, facilitating the development of more effective and sustainable mining additives.

Buzz pollination: investigations of pollen expulsion using the discrete element method.

Buzz pollination involves the release of pollen from, primarily, poricidal anthers through vibrations generated by certain bee species. Despite previous experimental and numerical studies, the intricacies of pollen dynamics within vibrating anthers remain elusive due to the challenges in observing these small-scale, opaque systems. This research employs the discrete element method to simulate the pollen expulsion process in vibrating anthers. By exploring various frequencies and displacement amplitudes, a correlation between how aggressively the anther shakes and the initial rate of pollen expulsion is observed under translating oscillations. This study highlights that while increasing both the frequency and displacement of vibration enhances pollen release, the rate of release does not grow linearly with their increase. Our findings also reveal the significant role of pollen-pollen interactions, which account for upwards of one-third of the total collisions. Comparisons between two types of anther exits suggest that pore size and shape also influence expulsion rates. This research provides a foundation for more comprehensive models that can incorporate additional factors such as cohesion, adhesion and Coulomb forces, paving the way for deeper insights into the mechanics of buzz pollination and its variability across different anther types and vibration parameters.

Visible light-driven triazine-based S-scheme COF-TpTt@BiOBr heterojunction with oxygen vacancy for enhanced photocatalytic pollutants removal and hydrogen production.

S-scheme heterojunction is an effective tactic to improve photocatalytic property. But few studies on constructing heterojunction with BiOBr and covalent organic frameworks (COFs) are available. Herein, a novel series of COF-TpTt@BiOBr S-scheme heterojunctions with oxygen vacancies (OVs) were constructed via solvothermal method. COF-TpTt@BiOBr-10% showed enhanced photocatalytic performance under visible light. Pollutants (such as Methyl Orange (MO), methylene blue (MB), Rhodamine B (RhB), tetracycline (TC) and Levofloxacin hydrochloride (LEV)) can be efficiently degraded and the photocatalytic H2 generation rate reached 10828.075 μmol g-1 h-1, which was 12.4 and 8.5 times of COF-TpTt and BiOBr. In addition, 3,3',5,5'-tetramethylbenzidine (TMB) oxidation experiment showed it has excellent molecular oxygen activation capacity. Furthermore, the S-scheme heterojunction charge transfer mechanism was proved by density functional theory (DFT) calculations. Under the influence of internal electric field, energy band bending and Coulomb force, e- and h+ were efficiently separated and transferred. The formation of S-scheme heterojunction and generation of multiple free radicals assured the high redox activity of COF-TpTt@BiOBr-10% photocatalytic system. This study strengthened our deep understanding of S-scheme heterojunction charge transfer mechanism and offered a new way for high efficient hydrogen energy production.

Physical Propagation of Consciousness: On Essence of Universal Gravitation and Coulomb Force

Physical Propagation of Consciousness: On Essence of Universal Gravitation and Coulomb Force

Interactions Between [PdX4]2- (X=Cl, Br) Dianions in Presence of Counterions.

The interaction between two square palladium (II) dianions PdX4 2- (X=Cl, Br) is evaluated by crystal study and analyzed by quantum chemical means. The arrangement within the crystal between each pair of PdX4 2- neighbors is suggestive of a Pd⋅⋅⋅X noncovalent bond, which is verified by a battery of computational protocols. While the potential between these two bare dianions is computed to be highly repulsive, the introduction of even just two counterions makes this interaction attractive, as does the presence of a constellation of point charges. It is concluded that there is indeed a stabilizing Pd⋅⋅⋅X bond, but it is incapable of overcoming the strong coulombic repulsive force between two dianions. While the QTAIM, NBO, and NCI tools can indicate the presence of a noncovalent bond, they are unable to distinguish an attractive from a repulsive interaction.

Venus cloud catcher as a proof of concept aerosol collection instrument

We report on the proof-of-concept of a low-mass, low-power method for collecting micron-sized sulfuric acid aerosols in bulk from the atmosphere of Venus. The collection method uses four wired meshes in a sandwich structure with a deposition area of 225 cm2. It operates in two modes: passive and electrostatic. During passive operation, aerosols are gathered on the deposition surface by aerodynamic force. During electrostatic operation, a tungsten needle discharges a high voltage of − 10 kV at the front of the grounded mesh structure. The discharge ionizes aerosols and attracts them to the mesh by Coulomb forces, resulting in improved efficiency and tentative attraction of submicron aerosols. We describe the instrument construction and testing in the laboratory under controlled conditions with aerosols composed of 25%, 50%, 70%, 80%, 90% and 98%* concentration by volume of sulfuric acid, the rest water. We demonstrated the following: (i) both modes of operation can collect the entire range of sulfuric acid solutions; (ii) the collection efficiency increases steadily (from a few percent for water to over 40% for concentrated sulfuric acid) with the increased concentration of sulfuric acid solution in water in both modes; (iii) the relative improvement in the collection of the electrostatic mode decreases as the sulfuric acid concentration increases. We also demonstrated the operation of the instrument in the field, cloud particle collection on Mt. Washington, NH, and crater-rim fumaroles’ particle collection on Kīlauea volcano, HI. The collection rate in the field is wind-speed dependent, and we observed collection rates around 0.1 ml in low wind environments (1–2 m), and around 1 ml in stronger wind (7–9 m).

The Schrödinger Equation Used the Wrong Energy Relationship

According to the energy relationship of the ground state solution of a hydrogen atom using the Schrödinger equation, the kinetic energy of an electron at twice the Bohr radius becomes zero. The electron has zero kinetic energy, which means it is dead, indicating that the energy relationship used in the Schrödinger equation is incorrect. Then, the reasons for both the chaotic energy relationship of the Schrödinger equation and the half frequency problem encountered by Bohr are analyzed. Bohr only considered Coulomb force and established an equation with centrifugal force, but he did not consider Lorentz force. So, the frequency he obtained must be multiplied by 1/2 to match the experimental value. This article also analyzes other issues related to the Schrödinger equation.

LDOS of electron pair and the role of the Pauli exclusion principle

The local density of states (LDOS) for a pair of non-relativistic electrons, influenced by repulsive Coulomb forces, is expressed in term of one-dimensional integrals over Whittaker functions. The computation of the electron pair's LDOS relies on a two-particle Green's function (GF), a generalization of the one-particle GF applicable to a charged particle in an attractive Coulomb potential. By incorporating electron spins and considering the Pauli exclusion principle, the resulting LDOS consists of two components: one originating from an exchange-even two-particle GF and the other from an exchange-odd two-particle GF. The calculated LDOS reveals its dependence on both inter-electron distance and energy. The pseudo-LDOS, derived from the two-body contribution to the LDOS, is examined. This term ensures complete LDOS suppression atr = 0, exhibiting a limited spatial extent, and the reasons for its emergence are elucidated. It is shown that for energies exceeding the effective Hartree energy and inter-electron distances beyond the effective Bohr radius, the impact of many-body contributions to the LDOS can be disregarded. The induced LDOS for an electron pair subjected to an attractive contact potential in two dimensions is evaluated. At small distancesafrom the potential center, a predicted relative difference in LDOS between even and odd state pair reaches approximately 8%. The calculated LDOS is compared with available experimental findings from a two-dimensional electron gas (2DEG). Both exhibit similar oscillation periods; however, the LDOS of the electron pair decays as1/a3, significantly faster than the1/adecay observed for free electrons in a 2DEG.

The analytical resolution of Klein–Gordon equation with vector and scalar for Coulomb plus Yukawa potentials

Similar to how general relativity emerged, quantum mechanics resulted from experimental observations that made us radically rethink our previous assumptions. Scientists who study atoms need to solve these three equations. They are for a system with N electrons affected by the nucleus’s attractive Coulomb force and the repulsive force between each pair of electrons and other potentials. While general relativity has upended our large-scale conception of the universe, quantum mechanics calls into question all our intuition regarding particle physics. The Klein–Gordon (KG) resolution helps determine some physical systems and their properties by finding their bound states and eigenfunctions. These are resolved using analytical and numerical methods, as well as Coulomb and Yukawa potentials. In order to extract some of the first eigenvalues of the quantum mechanical system, we applied the Nikiforov–Uvarov (NU) method to the KGequation. The findings are significant for understanding nuclear charge radius, spin, nuclear diffusion and other topics in numerous theoretical physics and quantum chemistry fields because they are more generic and helpful.

Molecular simulation methods of evaporating electrosprayed droplets

A robust methodology for molecular simulations of evaporating droplets that enables comparison between the dynamics of the process of interest and the solvent evaporation rate has already been developed (Oh and Consta, 2017). The competition of these dynamics will determine the mass spectrum. However, the success of the approach depends on the accurate and effective treatment of electrostatic forces. Often, in droplet simulations, bulk solution parametrized force-fields are used where the Coulomb forces are directly taken into account with a cut-off distance longer than the droplet diameter. On the one hand this approach is inefficient for large droplets because the computational cost increases as the square of the number of the atomic sites, and on the other hand the force field is slightly different from that has been parametrized for the bulk solution. The effect of this new force field in the conformations of macromolecules is still unknown. Multilevel summation method (MSM) has been developed (Hardy et al. 2015) for the efficient treatment of electrostatic forces in non-periodic and semi-periodic systems, charged or neutral. MSM maintains the same force field in droplets as in the bulk solution. We compare MSM with direct electrostatic treatment in droplets. The comparison shows free energy differences between conformations of short peptides along the radius of gyration order parameter that indicate the need for validation of the direct method. We demonstrate the usage of MSM to study Rayleigh jet formation and charge emission from droplets. We conclude that robust approaches for droplet simulations that can be used with a force field of any complexity are available and can be implemented within many of the available open-source molecular modeling softwares. In the near future, the presented approach may provide reliable reference mass spectra for experiments, where the deviations from the experimental data may reveal valuable information about the processes that take place within the instrument.

Accurate, Fast, and Non-Destructive Net Charge Measurement of Levitated Nanoresonators Based on Maxwell Speed Distribution Law

Nanoscale resonant devices based on optical tweezers are widely used in the field of precision sensing. In the process of driving the nanoresonator based on the Coulomb force, the real-time, precise regulation of the charge carried by the charged resonator is essential for continuous manipulation. However, the accuracy of the existing charge measurement methods for levitated particles is low, and these methods cannot meet the needs of precision sensing. In this study, a novel net charge measurement protocol for levitated particles based on spatial speed statistics is proposed. High-precision mass measurement based on Maxwell’s rate distribution law is the basis for improving the accuracy of charge measurement, and accurate measurement of net charge can be achieved by periodic electric field driving. The error of net charge measurement is less than 7.3% when the pressure is above 0.1 mbar, while it can be less than 0.76% at 10 mbar. This proposed method features real-time, high-precision, non-destructive, and in situ measurement of the net charge of particles in the medium vacuum, which provides new solutions for practical problems in the fields of high-precision sensing and nano-metrology based on levitated photodynamics.

Interfacial Proton Precompensation: Suppressing Deprotonation-Driven Lattice Collapse for Enhanced Efficiency and Stability in Perovskite Solar Cells.

The chemical property of the buried interface plays a crucial role in improving the performance and stability of perovskite solar cells (PSCs). The SnO2/perovskite interface prepared from SnO2 alkaline hydrogel with high proton affinity triggers directional migration and irreversible reactions of protons, exacerbating the disintegration of perovskite crystal. In this study, we proposed proton precompensation strategy to suppress the deprotonation effect of the buried interface and improve the durability of the devices. By modulating the chemical environment and surface energy state of the buried interface, the domain-limiting and spontaneous compensation of protons in formamidinium (FA+) under coulomb force were achieved, thereby stabilizing the perovskite crystal structure. The stability of target perovskite films under UV illumination and heating at 85 °C was significantly enhanced. As a result, the devices can retain around 90 % of their initial power conversion efficiency (PCE) after 1000 h of continuous irradiation at the maximum power point (MPP). Moreover, due to the reduction of defect content at the buried interface and the improvement of conductivity and carrier mobility by the precompensation treatment, the interfacial energy loss and non-radiative recombination were substantially diminished. The target PSC devices exhibited much higher PCE of 25.55 % than the control devices (23.03 %).

Interfacial Proton Precompensation: Suppressing Deprotonation‐Driven Lattice Collapse for Enhanced Efficiency and Stability in Perovskite Solar Cells

The chemical property of the buried interface plays a crucial role in improving the performance and stability of perovskite solar cells (PSCs). The SnO2/perovskite interface prepared from SnO2 alkaline hydrogel with high proton affinity triggers directional migration and irreversible reactions of protons, exacerbating the disintegration of perovskite crystal. In this study, we proposed proton precompensation strategy to suppress the deprotonation effect of the buried interface and improve the durability of the devices. By modulating the chemical environment and surface energy state of the buried interface, the domain‐limiting and spontaneous compensation of protons in formamidinium (FA+) under Coulomb force were achieved, thereby stabilizing the perovskite crystal structure. The stability of target perovskite films under UV illumination and heating at 85 °C was significantly enhanced. As a result, the devices can retain around 90% of their initial power conversion efficiency (PCE) after 1000 h of continuous irradiation at the maximum power point (MPP). Moreover, due to the reduction of defect content at the buried interface and the improvement of conductivity and carrier mobility by the precompensation treatment, the interfacial energy loss and non‐radiative recombination were substantially diminished. The target PSC devices exhibited much higher PCE of 25.55% than the control devices (23.03%).

Heat transfer enhancement for electro-thermo-convection of FENE-P viscoelastic fluid in a square cavity

This study numerically investigates the heat transfer enhancement for viscoelastic electro-thermo-convection in a two-dimensional differentially heated cavity with injection from below. The flow motion is assumed to be incompressible, which is driven by the Coulomb force and the thermal buoyant force. The polymers are described by the FENE-P model which exhibits typical shear-thinning and elastic properties. Based on the extensibility parameter (L), the cases are divided into several scenarios, corresponding to weak elasticity with strong shear-thinning, moderate elasticity with moderate shear-thinning, and strong elasticity with weak shear-thinning, respectively. We find that the competition between the shear-thinning and elasticity dominates the flow state and heat transport. The shear-thinning effect tends to facilitate heat transfer, while its elastic properties tend to decrease it. In the scenario of weak elasticity with strong shear-thinning (L2=10), the polymer additives significantly improve the heat transfer enhancement (HTE) of the electric field as the polymer viscosity ratio (β) decreases or Weissenberg number (Wi) increases, where the maximum HTE reaches around 92.1%. The amount of HTE first increases rapidly with Wi but then remains almost constant once a critical Wi is exceeded. However, the HTE significantly decreases in the scenario of strong elasticity with weak shear-thinning (300≤L≤1000) since the elasticity dominates over the shear-thinning. These heat transfer performances are then corroborated with the boundary layer and kinetic energy budget analysis.

The additionally charged forces in the Sun-Earth and Earth-Moon systems

We build a model to describe the net charges existing in the Sun and Earth. According to statistical mechanics, electrons on average move much faster than protons and neutrons at the same temperature. Electrons escape the Sun more easily than protons and neutrons, so the Sun becomes a charged star. We estimate the maximal net charges in the Sun by using statistical mechanics first. Then, we analyze the dynamical cycles between the positive and negative charged states. At a distance far away from the Sun, the effective net charges including the leaving protons and electrons are about 6.3×109C with energies of 1 GeV initially. We also use another way based on the observations of the Earth's perihelion precession to estimate the minimum and maximum net charges between 1.15×108C and 2.80×1010C in space from the Sun to Earth. The most charged particles from the Sun to the Earth are electrons, so both the Moon and Earth are impacted by them and very possibly have the same electricity. Next, we propose new physical mechanisms causing the slowdown of the Earth's spin and propose Coulomb's repulsive force resulting in the increasing distance between the Moon and Earth. As a result, it gives the net charges of 1.11×106C surrounding the Earth and 8.29×103C surrounding the Moon. Our estimations also correspond to early works. The charges surrounding the Sun and Earth cause the Earth to be long-term accelerated in the radial direction by Coulomb's force. Finally, using the effective net charges of the Sun and Earth, we calculate the increasing distance between 11.4 m and 19.4 m on average per century if the initial radial velocities of the Earth are in between 3.59×10−9m/s and 6.12×10−9m/s, which satisfies the observed reports.

F−surface modified ZnO for enhanced photocatalytic H2O2production and its fs-TAS investigation

Pure ZnO exhibits low photocatalytic H2O2 production activity due to the rapid charge recombination. To realize the spatial separation of photogenerated electrons and holes, constructing an electron transfer channel on the ZnO surface is an effective approach. This study successfully modified the surface of ZnO using F– (ZnO/F) by introducing NH4F in an aqueous phase photocatalytic system. The F– is adsorbed on the ZnO surface by Coulombic force and significantly improves the photocatalytic H2O2 production performance of ZnO, with the highest efficiency of 4137.2 μmol·g–1·L–1·h–-1. The photocatalytic performance enhancement mechanism of ZnO/F is explained in terms of electron transfer dynamics by femtosecond transient absorption spectroscopy (fs-TAS) measurements. F– surface modification constructs a new ultrafast electron transport pathway from the ZnO CB to F–, and the optimal ZnO/F exhibits the fastest interfacial electron transfer lifetime of 5.8 ps. The F– surface modification effectively facilitates the charge separation, thereby increasing the number of electrons available for photocatalytic H2O2 reaction. This study has revealed the roles of F– surface modification in the photocatalytic H2O2 production by ZnO and provides guidance for ionic modification to improve photocatalytic performance.