Molecular dynamics simulation of the aggregation phenomenon in the late stages of silica materials preparation

Modeling Colloidal Particle Aggregation Using Cluster Aggregation with Multiple Particle Interactions

In this study, we investigate the aggregation dynamics of colloidal silica by generating simulated structures and comparing them to experimental data gathered through scanning transmission electron microscopy (STEM). More specifically, diffusion-limited cluster aggregation and reaction-limited cluster aggregation models with different functions for the probability of particles sticking upon contact were used. Aside from using a constant sticking probability, the sticking probability was allowed to depend on the masses of the colliding clusters and on the number of particles close to the collision between clusters. The different models of the sticking probability were evaluated based on the goodness-of-fit of spatial summary statistics. Furthermore, the models were compared to the experimental data by calculating the structures' fractal dimension and mass transport properties from simulations of flow and diffusion. The sticking probability, depending on the interaction with multiple particles close to the collision site, led to structures most similar to the STEM data.

An ab initio molecular dynamics investigation of the behaviour of amorphous substances in anodic aluminium oxide under electric field

In order to elucidate the diffusion behaviour of ions in alumina during the anodic alumina process, the effects of electric field strength, hydration content, and electrolyte on amorphous alumina and hydrated alumina were studied using ab initio molecular dynamics. The results show that the diffusion rate of ions in alumina increases with the increase in electric field strength, but there is an extreme value. The maximum diffusion rate of Al ions in alumina monohydrate is 21.8 μm2/ms/V, while in alumina trihydrate, it is 16.7 μm2/ms/V. The ionic diffusion rate of hydrated alumina is one to two orders of magnitude larger than that of anhydrous amorphous alumina due to the effect of the drag of H ions, which reduces the migration activation energy. Electrolytes also affect the diffusion rate of alumina through the action of H ions. The increase in H ions will not only enhance the diffusion rate of hydrated alumina but also render the hydrous compound more vulnerable to breakdown.

Bipolar Molecular Torque Wrench Modulates the Stacking of Two-Dimensional Metal-Organic Framework Nanosheets

The precise modulation of nanosheet stacking modes introduces unforeseen properties and creates momentous applications but remains a challenge. Herein, we proposed a strategy using bipolar molecules as torque wrenches to control the stacking modes of 2-D Zr-1,3,5-(4-carboxylphenyl)-benzene metal-organic framework (2-D Zr-BTB MOF) nanosheets. The bipolar phenyl-alkanes, phenylmethane (P-C1) and phenyl ethane (P-C2), predominantly instigated the rotational stacking of Zr-BTB-P-C1 and Zr-BTB-P-C2, displaying a wide angular distribution. This included Zr-BTB-P-C1 orientations at 0, 12, 18, and 24° and Zr-BTB-P-C2 orientations at 0, 6, 12, 15, 24, and 30°. With reduced polarity, phenyl propane (P-C3) and phenyl pentane (P-C5) introduced steric hindrance and facilitated alkyl hydrophobic interactions with the nanosheets, primarily resulting in the modulation of eclipsed stacking for Zr-BTB-P-C3 (64.8%) and Zr-BTB-P-C5 (93.3%) nanosheets. The precise angle distributions of four Zr-BTB-P species were in agreement with theoretical calculations. The alkyl induction mechanism was confirmed by the sequential guest replacement and 2-D 13C-1H heteronuclear correlation (HETCOR). In addition, at the single-particle level, we first observed that rotational stacked pores exhibited similar desorption rates for xylene isomers, while eclipsed stacked pores showed significant discrepancy for xylenes. Moreover, the eclipsed nanosheets as stationary phases exhibited high resolution, selectivity, repeatability, and durability for isomer separation. The universality was proven by another series of bipolar acetate-alkanes. This bipolar molecular torque wrench strategy provides an opportunity to precisely control the stacking modes of porous nanosheets.

Long-Life Lithium-Ion Sulfur Pouch Battery Enabled by Regulating Solvent Molecules and Using Lithiated Graphite Anode

The development of lithium-sulfur (Li-S) batteries is severely limited by the shuttle effect and instability of Li-metal anode. Constructing Li-ion S batteries (LISBs), by using more stable commercial graphite (Gr) anode instead of Li-metal, is an effective way to realize long-cycle-life Li-S batteries. However, Gr electrode is usually incompatible with the ether-based electrolytes commonly used for Li-S batteries due to the Li+ -ether complex co-intercalation into Gr interlayers. Herein, a solvent molecule structure regulation strategy is provided to weaken the Li+ -solvent binding by increasing steric hindrance and electronegativity, to accelerate Li+ de-solvation process and prevent Li+ -ether complex co-intercalation into Gr anode. Meanwhile, the weakly solvating power of solvent can suppress the shuttle effect of lithium polysulfides and makes more anions participate in Li+ solvation structure to generate a stable anion-derived solid electrolyte interface on Gr surface. Therefore, a LISB coin-cell consisting of lithiated graphite anode and S@C cathode displays a stable capacity of ≈770 mAh g-1 within 200 cycles. Furthermore, an unprecedented practical LISB pouch-cell with a high Gr loading (≈10.5 mg cm-2 ) also delivers a high initial capacity of 802.3 mAh g-1 and releases a stable capacity of 499.1 mAh g-1 with a high Coulombic efficiency (≈95.9%) after 120 cycles.

Co-Intercalation-Free Ether-Based Weakly Solvating Electrolytes Enable Fast-Charging and Wide-Temperature Lithium-Ion Batteries

Ether-based electrolytes are competitive choices to meet the growing requirements for fast-charging and low-temperature lithium-ion batteries (LIBs) due to the low viscosity and low melting point of ether solvents. Unfortunately, the graphite (Gr) electrode is incompatible with commonly used ether solvents due to their irreversible co-intercalation into Gr interlayers. Here, we propose cyclopentyl methyl ether (CPME) as a co-intercalation-free ether solvent, which contains a cyclopentane group with large steric hindrance to obtain weakly solvating power with Li+ and a wide liquid-phase temperature range (-140 to +106 °C). A weakly solvating electrolyte (WSE) based on CPME and fluoroethylene carbonate (FEC) cosolvents can simultaneously achieve fast desolvation ability and high ionic conductivity, which also induces a LiF-rich solid electrolyte interphase (SEI) on the Gr anode. Therefore, the Gr/Li half-cell with this WSE can deliver outstanding rate capability, stable cycling performance, and high specific capacity (319 mAh g-1) at an ultralow temperature of -60 °C. Furthermore, a practical LiFePO4 (loading ≈25 mg cm-2)/Gr (loading ≈12 mg cm-2) pouch cell with this WSE also reveals outstanding rate capability and stable long-term cycling performance above 1000 cycles with a high Coulombic efficiency (≈99.9%) and achieves an impressive low-temperature application potential at -60 °C.

Regulation of recombinant humanized collagen on HAP growth and its molecule simulation

Hydroxyapatite (HAP) in natural bone is formed under the regulation of natural collagen I. Here, we report how recombinant humanized collagen I (rhCol I) regulates the growth of HAP nanocrystals in a long belt shape 100-150 nm in width and 200-300 nm in length. MD simulation results showed that the interactions between rhCol I and the (001), (100), and (211) planes of HAP mainly contributed to the electrostatic force and van der Waals forces via COO⋯Ca, -NH⋯Ca, CH⋯OPO3, and NH⋯OPO3 bonds, respectively. On the (001) plane, the interaction between -COO- and Ca was stronger than on the (100) and (211) planes, resulting in a large electrostatic force, which inhibited the growth of the (001) plane. The lowest energy of adsorption to the (211) plane resulted in the preferential growth of the (211) plane due to the weakest interaction with rhCol I. The detailed correlation between HAP and rhCol I could explain HAP growth under regulation by rhCol I. This study provides a reference for the bio-application of recombinant collagen.

High-Energy-Density Lithium Metal Batteries with Impressive Li+ Transport Dynamic and Wide-Temperature Performance from -60 to 60 °C

High-energy-density Li metal batteries (LMBs) with Nickel (Ni)-rich cathode and Li-metal anode have attracted extensive attention in recent years. However, commercial carbonate electrolytes bring severe challenges including poor cycling stability, severe Li dendrite growth and cathode cracks, and narrow operating temperature window, especially hardly work at below -40 °C. In this work, a 2.4 m lithium difluoro(oxalato)borate (LiDFOB) in ethyl acetate (EA) solvent with 20 wt% fluorocarbonate (FEC) (named 2.4m-DEF) is designed to solve Li⁺ transport dynamic at low temperature and improve interfacial stability between electrolyte with Li anode or Ni-rich cathode. Beneficial lower freezing point, lower viscosity, and higher dielectric constant of EA solvent, the electrolyte exhibits excellent Li⁺ transport dynamic. Relying on the unique Li⁺ solvation structure, more DFOB^- anions and FEC solvents are decomposed to establish a stable solid electrolyte interface at electrolyte/electrode. Therefore, LiNi_0.9 Co_0.05 Mn_0.05 O₂ (NCM90)/Li LMB with 2.4m-DEF enables excellent rate capability (184 mA h g^-1 at 30 C) and stable cycling performance with ≈93.7% of capacity retention after 200 cycles at 20 C and room temperature. Moreover, the NCM90/Li LMB with 2.4m-DEF exhibits surprising ultra-low-temperature performance, showing 173 mA h g^-1 at -40 °C and 152 mA h g^-1 at -60 °C, respectively.

Solubility Determination and Comprehensive Analysis of the New Heat-Resistant Energetic Material TNBP

To improve the crystal quality of 4,8-bis(2,4,6-trinitrophenyl)difurazolo [3,4-b:3′,4′-e] pyrazine (TNBP), the solubility of TNBP in organic solvents (six pure and four mixed solvents) was determined by the laser monitoring technique from 293.15 to 353.15 K. The results showed that the solubility was positively correlated with the increase in the experimental temperature and the main solvent content, except for the co-solvent phenomenon in the DMSO + ethyl acetate solvent mixture. To explain the dissolution behavior of TNBP, the KAT-SER model was analyzed for pure solvent systems, and it was found that hydrogen bonding alkalinity and self-cohesiveness were the main influencing factors. The free energy of solvation and radial distribution function of TNBP in mixed solvents were also obtained by molecular dynamics simulation, and the effect of solute–solvent and solvent–solvent interactions on the solubility trend was analyzed. The experimental data were correlated using three empirical equations (van’t Hoff equation, modified Apelblat equation, and λh equation), and the deviation analysis showed the good applicability of the modified Apelblat model. Furthermore, the dissolution of TNBP was heat-absorbing and not spontaneous, according to the thermodynamic characteristics estimated by the van’t Hoff equation.

Hierarchical Materials from High Information Content Macromolecular Building Blocks: Construction, Dynamic Interventions, and Prediction

Hierarchical materials that exhibit order over multiple length scales are ubiquitous in nature. Because hierarchy gives rise to unique properties and functions, many have sought inspiration from nature when designing and fabricating hierarchical matter. More and more, however, nature's own high-information content building blocks, proteins, peptides, and peptidomimetics, are being coopted to build hierarchy because the information that determines structure, function, and interfacial interactions can be readily encoded in these versatile macromolecules. Here, we take stock of recent progress in the rational design and characterization of hierarchical materials produced from high-information content blocks with a focus on stimuli-responsive and "smart" architectures. We also review advances in the use of computational simulations and data-driven predictions to shed light on how the side chain chemistry and conformational flexibility of macromolecular blocks drive the emergence of order and the acquisition of hierarchy and also on how ionic, solvent, and surface effects influence the outcomes of assembly. Continued progress in the above areas will ultimately usher in an era where an understanding of designed interactions, surface effects, and solution conditions can be harnessed to achieve predictive materials synthesis across scale and drive emergent phenomena in the self-assembly and reconfiguration of high-information content building blocks.

Ultralow Adhesion and Phase Change Behaviors of Sulfur Droplets on the Superhydrophobic Surface and Its Application in the Granulation Process

Traditional sulfur granulation process is often accompanied by high dust and mechanical friction, which are dangerous and harmful to the environment. In this work, the application of the superhydrophobic surface to sulfur granulation is expected to solve the above problem. Two superhydrophobic metal sheets were prepared, and the rolling angles of the two samples are both less than 10°. The contact angles of liquid sulfur are 152.7 ± 0.5 and 151.3 ± 0.1°, respectively. The adhesion rates of both samples are less than 0.5 wt %. The solidifying process of a sulfur drop on the superhydrophobic surface was recorded and simulated, conforming that the substrate temperature has a great influence on the solidifying process. Based on the above findings, static granulation and rolling to granulation were proposed. The product obtained by the two methods has uniform particle size distribution and excellent compressive strength, showing a good industrial application prospect. This study provides a referral strategy for an economical and environmentally friendly sulfur granulation process.

Biomimetic Growth of Hydroxyapatite on SiO2 Microspheres to Improve Its Biocompatibility and Gentamicin Loading Capacity

The interest in multifunctional biomaterials to be implanted are also able to release drugs that reduce pain and inflammation or prevent a possible infection has increased. Bioactive materials such as silica (SiO₂) containing surface silanol groups contribute to the nucleation and growth of hydroxyapatite (HAp) in a physiological environment. Regarding biocompatibility, the spherical shape of particles is the desirable one, since it does not cause mechanical damage to the cell membrane. In this work, the synthesis of SiO₂ microspheres was performed by the modified Stöber method and they were used for the biomimetic growth of HAp on their surface. The effect of the type of surfactant (sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB), and polyethylene glycol (PEG)), and heat treatment on the morphology and size of SiO₂ particles was investigated. Monodisperse, spherical-shaped SiO₂ microparticles with an average particle size of 179 nm, were obtained when using PEG (SiO₂-PEG). The biomimetic growth of HAp was performed on this sample to improve its biocompatibility and drug-loading capacity using gentamicin as a model drug. Biomimetic growth of HAp was confirmed by FTIR-ATR, SEM-EDX and TEM techniques. SiO₂-PEG/HAp sample had a better biocompatibility in vitro and gentamicin loading capacity than SiO₂-PEG sample.

Molecular Cage-Mediated Radial Gradient Porous Sponge Nanofiber for Selective Adsorption of a Mustard Gas Simulant

Poisons and poisonous weapons in armed conflict, especially chemical warfare agents (CWAs), pose serious threats to global security. Porous materials have recently been regarded as promising candidates to defend personnel in a CWA-contaminated environment, but challenges remain for integrating these materials into protective garments without sacrificing the intrinsic flexibility of fibers. Here, we report a rigid-flexible coupling hypercross-linking methodology to create flexible sponge-like nanofibers featuring hierarchical radial gradient porous nanoarchitectures, in which the inner structure is a mesoporous multichambered network, and the outer structure is a dense domain with a microporous network structure. Experimental and computational evidence supports the contention that sponge nanofibers with distinctive pore topology and robust bendability can be designed by manipulating the flexibility of building blocks. The resulting heterogeneous nanofibers exhibit integrated properties of spatially selective superstructures, abundant micropores, interconnected mesopores, a high surface area (579 m² g^-1), remarkable flexibility, and exceptional CWA affinity, which are extraordinarily effective for adsorptive performance (498 mg g^-1). The successful synthesis of these materials might inspire the development of chemical protective materials in an efficient, self-standing, and structurally adaptive form.

Systematic thermodynamic analysis of apremilast polymorphs via solubility measurement with modeling: Mechanism evaluation through molecular simulation

The polymorphism of apremilast has been investigated. Two polymorphs have been identified and characterized by differential scanning calorimeter, fourier transform infrared spectroscopy, and powder X-ray diffractometer. Solubilities of apremilast forms B and E in three binary solvents of methanol-water, acetonitrile-water, and acetonitrile-methanol have been measured using the static method at a temperature ranging from 288.15 K to 328.15 K under standard atmospheric pressure. Subsequently, the solubility data have been analyzed using the Wilson, NRTL, and UNIQUAC thermodynamic models, respectively. Furthermore, the Gibbs energy of solution and the radial distribution function have been calculated using the molecular simulation method to evaluate the dissolution mechanism. The Gibbs energy of solution reveals that the rank of solute-solvent interaction correlated well with solubility order in binary solvent mixtures, and the radial distribution function indicates that weakening of solvent-solvent interaction led to an increase in solubility.

Penetration and Displacement Behavior of N2 in Porous Interlayer Structures Containing Water/Salt Component by Molecular Dynamics Simulation

The penetration and displacement behavior of N₂ molecules in porous interlayer structures containing a water/salt component with porosities of 4.29%, 4.73%, 5.17%, 7.22%, and 11.38% were explored using molecular dynamics simulations. The results demonstrated that the large porosity of the interlayer structures effectively enhanced the permeation and diffusion characteristics of N₂. The water and salt in the interlayer structures were displaced during the injection of N₂ in the porosity sequence of 4.29% < 4.73% < 5.17% < 7.22% < 11.38%. The high permeance of 7.12 × 10⁻⁶ indicated that the interlayer structures with a porosity of 11.38% have better movability. The strong interaction of approximately 15 kcal/mol between N₂ and H₂O had a positive effect on the diffusion of N₂ and the displacement of H₂O before it reached a stable equilibrium state. The distribution of N₂ in porous interlayer structures and the relationship between the logarithm of permeability and breakthrough pressure were presented. This work highlighted the effects of porosity on the permeability and diffusion of N₂/H₂O in the interlayer, thus providing theoretical guidance for the development of petroleum resources.

Influence of Pore Size and Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores: A Molecular Dynamics Simulation

The transport properties of chloride ions in cement-based materials are one of the major deterioration mechanisms for reinforced concrete (RC) structures. This paper investigates the influence of pore size and fatigue loading on the transport properties of NaCl in C-S-H nanopores using molecular dynamics (MD) simulations. Molecular models of C-S-H, NaCl solution, and C-S-H nanopores with different pore diameters are established on a microscopic scale. The distribution of the chloride ion diffusion rate and the diffusion coefficient of each particle are obtained by statistically calculating the variation of atomic displacement with time. The results indicate that the chloride ion diffusion rate perpendicular to C-S-H nanopores under fatigue loading is 4 times faster than that without fatigue loading. Moreover, the diffusion coefficient of water molecules and chloride ions in C-S-H nanopores increases under fatigue loading compared with those without fatigue loading. The diffusion coefficient of water molecules in C-S-H nanopores with a pore size of 3 nm obtained from the MD simulation is 1.794 × 10⁻⁹ m²/s, which is slightly lower than that obtained from the experiment.

Thin-film composite membrane breaking the trade-off between conductivity and selectivity for a flow battery

A membrane with both high ion conductivity and selectivity is critical to high power density and low-cost flow batteries, which are of great importance for the wide application of renewable energies. The trade-off between ion selectivity and conductivity is a bottleneck of ion conductive membranes. In this paper, a thin-film composite membrane with ultrathin polyamide selective layer is found to break the trade-off between ion selectivity and conductivity, and dramatically improve the power density of a flow battery. As a result, a vanadium flow battery with a thin-film composite membrane achieves energy efficiency higher than 80% at a current density of 260 mA cm⁻², which is the highest ever reported to the best of our knowledge. Combining experiments and theoretical calculation, we propose that the high performance is attributed to the proton transfer via Grotthuss mechanism and Vehicle mechanism in sub-1 nm pores of the ultrathin polyamide selective layer.

Low-cost flow batteries with high power density are promising for energy storage, but membranes with simultaneously high ion conductivity and selectivity should be developed. Here the authors report a thin-film composite membrane that breaks the trade-off between ion conductivity and selectivity.