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Silicone rubber foam (SRF) is a kind of polymer material with excellent performance but flammable. The flame-retardant SRF was prepared with diatomite (Dia) and hexaphenoxycyclotriphosphazene (HPCTP) as flame retardants. Cone calorimetry tests (CCT), scanning electron microscopes (SEM) and mechanical tests were used to investigate the effects of Dia and HPCTP on the flame retardancy, smoke suppression and mechanical properties of SRF. The results showed that Dia and HPCTP had a synergistic effect on flame retardancy and smoke suppression. With the addition of 5 wt% Dia and 5 wt% HPCTP, the peak heat release rate (PHRR), the total heat release rate (THR), the peak smoke release rate (PSPR) and the total smoke production (TSP) of SRF decreased by 54.43, 37.64, 62.3 and 58%, respectively. With the addition of Dia and HPCTP, the thickness of the carbon layer became thicker, the cracks became smaller and the microstructure became denser. In addition, when the contents of 5 wt% Dia and 5 wt% HPCTP were added, the mechanical properties of SRF were the best; the tensile strength increased to 0.195 MPa, and the elongation at break increased by 109.85%. It provided a new flame-retardant method for SRF. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is a highly toxic, and flammable acid gas that is widely present in confined spaces. However, conventional adsorption materials are inefficient and have poor reuse properties. Metal‐organic frameworks (MOFs) show potential viability as novel materials in gas adsorption. Herein, mainstream MOFs were investigated based on molecular simulation techniques to explore the differences contributing to H2S adsorption. The adsorption process of H2S in MOFs was simulated by Grand Canonical Monte Carlo (GCMC) method, and the diffusion behavior was investigated based on molecular dynamics (MD) simulations. The results showed that the interaction energy and isosteric heat of adsorption were important criteria for determining the adsorption performance of H2S. The regulation of open metal sites could help to further enhance the adsorption of H2S, and the pore structure of MOFs affected the capture of H2S. A higher self‐diffusion rate implies faster H2S capture. Hydrogen bonds affect the trapping efficiency of MOFs for H2S and the relative positions of ligands in the benzene ring cause subtle differences in adsorption. This study provides design strategies for the improvement of new high‐performing MOFs for H2S adsorption in confined spaces. [ABSTRACT FROM AUTHOR]

Talcum powder is one of the leading causes of pneumoconiosis, adding compound surfactants to the dust removal process can significantly increase the effectiveness of the dust removal. Therefore, it is of great significance to study the effect of compound surfactants on the wettability of talcum powder. This paper focuses on the ability of compound surfactants to increase the wettability of talcum powder surface by using Materials Studio 8.0. The simulation results were analyzed from the water adsorbed amount, interaction energy, and water molecule concentration profile. Combined with the experimental data of contact angle, the optimal surfactant compounding method was obtained. The simulation results revealed that stable adsorption structures can be formed by the compound of anionic and nonionic surfactants, which can reduce the electrostatic repulsion between anionic surfactants effectively and promote the directional arrangement of nonionic surfactants on the talcum powder surface. When the molar ratio of sodium dodecyl sulfate (SDS) and Polysorbate 80 was 0.4:0.6, the amount of absorbed water reached 113, which is better than monomers and other compound surfactants. The contact angle experiment results indicated a consistent variation law with the simulation results. The contact angle decreased from 68.48° to 19.84° using the compounding method mentioned above, which has the optimum wetting effect among the four compounding methods. The research results will provide a reference for the application of compound surfactants in talcum powder dustproof work. [ABSTRACT FROM AUTHOR]

To enhance the flame retardancy and smoke suppression of silicone rubber foams (SRFs), a novel flame retardant, zinc borate-graphite intercalation compound (ZB-GIC), was synthesized and used in conjunction with Fe 2 O 3. The results showed that ZB-GIC markedly improved the flame retardancy and smoke suppression of SRFs, and Fe 2 O 3 significantly improved the smoke suppression of SRFs. ZB-GIC and Fe 2 O 3 had an excellent synergistic effect on flame retardant and smoke suppression. 5 wt% ZB-GIC synergistically with 5 wt% Fe 2 O 3 resulted in SRFs passing the UL-94 V-0 rating, whose limiting oxygen index (LOI) value reached up to 43.7%. Its peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), and total smoke production (TSP) decreased by 67.42%, 89.55%, 76.86%, and 91.67% compared to pure SRF. The ZB-GIC produced incombustible gas and a large amount of H 2 O when heated, which reduced the intensity of gas-phase combustion. The ZB filled the interlayer gaps formed after the expansion of GIC to enhance the strength of the char layer, and Fe 2 O 3 further strengthened the char layer. Our work has greatly reduced the fire hazards of SRFs and provided a promising flame retardant for the large-scale production of high-performance SRFs. ● A novel flame retardant ZB-GIC was synthesized. ● Fe 2 O 3 was used for the first time to improve the fire safety of SRFs. ● ZB-GIC/Fe 2 O 3 signally improved the flame retardancy and smoke suppression of SRFs. ● The flame retardant and smoke suppression mechanisms of ZB-GIC/Fe 2 O 3 were revealed. [ABSTRACT FROM AUTHOR]

By studying the key mechanical properties and their damage mechanisms of coal at the nanoscale, a better understanding of the strength and damage of coal in complex stress environments can be obtained. The micro-mechanical properties and damage mechanism of coal under cyclic loading were investigated by nanoindentation experiment and molecular dynamics (MD) simulation of nanoindentation. Molecular dynamics simulations were conducted by building models containing approximately 2.5 million atoms, it was found that the coal substrate showed cyclic hardening under cyclic loading. The hardness and elastic modulus of the coal samples measured by the nanoindentation experiment gradually increased from 0.476 GPa to 0.740 GPa and from 4.70 GPa to 5.997 GPa, respectively. The simulation results display a good agreement with the experimental results. The simulation results show that the plastic damage of coal substrate under cyclic loading is related to the stretching, bending, rotation, and fracture of chemical bonds. At the same time, the formation and recovery of elastic deformation are related to the changes of van der Waals force, Coulomb force, and bond angle. Additionally, the carbon hexatomic ring in the coal macromolecule is critical in resisting the influence of loading. [ABSTRACT FROM AUTHOR]

This work provides a more favorable implementation of synergistic drag reduction strategies based on molecular simulations of the strength of polymer-surfactant interactions. The simulated preferred system identifies polyethylene oxide (PEO) and guar gum (GG) as polymers, and dodecyl dimethyl benzyl ammonium chloride (DDBAC) and dodecyl hydroxy sulfobetaine (DHSB). To forecast the drag reduction capability and identify the drag reduction process, important elements such as aggregation phenomena, charge distribution, shear deformation, and interfacial behavior were examined. Experimental measurements of viscosity, surface tension, and drag reduction validate the interactions. It was found that the compound system demonstrates enhanced viscosity, surface tension, and drag reduction efficiency compared to individual systems. The PEO-DHSB system achieves a drag reduction rate of 63.68% during initial flow, while the GG-DHSB system maintains a rate of 47.26% even after prolonged water circulation. This work visualizes the poly-surface aggregation phenomenon using the density distribution of surfactant hydrophobic tail chains, dynamically demonstrating the deformation of polymer and surfactant molecules during the shear process and interfacial behavior, and providing molecular-scale intuitive insights for understanding the drag reduction mechanism of poly-surface systems. Meanwhile, by comparing the effects of molecular type and structure on poly-surface interactions and drag reduction performance, it provides a theoretical foundation for the development and application of subsequent poly-surface drag reduction schemes, thereby broadening the application of drag reduction technology in the field of energy conservation and emission reduction. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The addition of the polymer improved the hydrophobicity of the polyurethane surface. • PAM and PEO combine directly with hydrophobic surfaces and form a cover layer. • XG and GG form aggregates with water first and then transfer to hydrophobic surfaces. • PAM-polyurethane hydrophobic surface has a better synergistic effect than others. The drag reduction synergy of four types of high-molecular polymers, namely polyacrylamide, poly(ethylene oxide), xanthan gum, and guar gum, with polyurethane hydrophobic surfaces, was investigated by both experiments and molecular simulations. The synergistic mechanisms of polymers and hydrophobic surfaces were revealed using Monte Carlo and molecular dynamics simulations in terms of interfacial interactions between polymers and water molecules, intermolecular interactions, and the adsorption conformation of polymers on hydrophobic surfaces. The addition of the polymer improved the hydrophobicity of the polyurethane surface, with flexible polymers having a more substantial effect than rigid polymers, according to both simulations and contact angle experiments. Furthermore, based on the transient configuration of polymer and water molecules moving on the hydrophobic surface, the kinetic process is divided into three stages: water molecule aggregation, water molecule-induced deformation, and polymer extension on the hydrophobic surface. Meanwhile, PAM and PEO combine directly with hydrophobic surfaces and form a cover layer with water molecules, whereas XG and GG prefer to form aggregates with water molecules first and then transfer to hydrophobic surfaces. The PAM-polyurethane hydrophobic surface, in particular, has a better synergistic effect than others, and its synergistic mechanism is related to the larger radius of gyration, stronger interaction with water molecules, and higher stability of the drag reduction system. [ABSTRACT FROM AUTHOR]

Coal dust in the coal mining process may lead to a serious threat to the safety and health of miners. The addition of surfactants during coal seam water infusion can significantly improve the effect of dust suppression, so it is crucial to study the influence mechanism of surfactants on coal wettability. The variation of the hydration film thickness on the Tunliu coal surface at different concentrations of sodium dodecylbenzene sulfonate (SDBS) solution was investigated by atomic force microscopy. The experimental results indicate that the hydration film thickness increases initially and decreases afterward with the SDBS solution concentration increase, with a maximum value of 11.4 nm. The surface free energy (SFE) of coal molecules adsorbed with different numbers of SDBS molecules were calculated using two coal molecule cell models developed by Materials studio 8.0, and the simulation results display a good agreement with the experiments. The higher the SFE, the greater the hydration film thickness on the coal surface, and the stronger the enhancement effect of SDBS solution on the wettability of coal at the corresponding concentration. The interface formation energy (IFE) and cohesive energy density (CED) of coal molecules after adsorption of SDBS molecules were calculated separately. It was found that when three SDBS molecules were adsorbed, the absolute value of IFE and CED reached the maximum, and each SDBS molecule had the strongest average effect on coal molecules, the bond between them would be tighter. SFE simulations are helpful to optimize the selection of surfactants for practical engineering applications. [ABSTRACT FROM AUTHOR]

The surfactant can effectively improve the wetting effect of the solution on coal and improve the dust removal efficiency of coal dust, which is of great significance to mine dust control. To investigate the effect of alkyl chain length of surfactants on the wettability of low rank coal, ionic surfactants with different chain length structures were selected, and molecular dynamics and quantum chemistry simulation methods were used to reveal the effect of alkyl chain length on the wettability of low rank coal at the molecular level. The simulation results show that with the increase of alkyl chain length, the absolute value of coal-water interface formation energy increases gradually, and reaches the maximum when the chain length is 16. The wetting effect of anionic surfactant is better than that of cationic surfactant. Surfactants C 16 SNa and C 16 TAB show isotropy at the coal-water interface, which is beneficial to increase the adsorption thickness between coal and water and improve the wettability of low rank coal. The alkyl chain length mainly affects the hydrophobic interaction between surfactants and coal molecules, and then regulates the wettability of low rank coal surfaces. When the alkyl chain is longer than 16, the steric hindrance of surfactant molecules is large, which is not conducive to improving the wettability of low rank coal surface. The settlement experiment and contact angle experiment show that C 16 TAB has the best wetting effect on low rank coal, which is basically consistent with the simulation results. This study provides a basis for the molecular structure design of new high-efficiency surfactants. [Display omitted] • C 16 SNa and C 16 TAB exhibit isotropy at the coal-water interface. • Surfactants with chain length of 16 have the best wetting effect on coal surface. • The alkyl chain mainly affects the hydrophobic bonding between surfactant and coal. • The steric hindrance effect weakens the wettability of surfactants on coal. [ABSTRACT FROM AUTHOR]

• Alkyl amine/APT hydrophobic effect is best than other types. • ODA/APT has the lowest surface energy with a maximum contact angle of 166.21°. • The hydrophobicity improves with increasing carbon chain for the same type of material. • ODA /SA/APT composite system has the best hydrophobicity. Material modification with low surface energy can offer lower surface free energy on micro- and nano-rough structures, which is necessary for developing superhydrophobic surfaces. Based on experiment and molecular simulation, the composite systems of attapulgite (APT) modified by alkylamine, alkylammonium salt and stearic acid were prepared. Combine surface free energy, electrostatic potential distribution, self-diffusion coefficient, and interfacial formation energy to favor the superhydrophobic composite system, and the interaction between low surface materials and attapulgite was explained. The results demonstrate that the hydrophobicity of APT are clearly modified by alkyl amine, alkyl ammonium salt, and stearic acid, and that when the molecular number of low surface energy monomers increases, the surface free energy of the composites first decreases and then increases. At the ideal concentration, the contact angles of alkyl amine/APT and SA/APT composites are all greater than 150°, and the antifouling performance is excellent. Finally, compounding technology was used to further optimize the superhydrophobic composite system. It was discovered that the hydrophobicity and antifouling properties of the composite system were superior to those of the monomer, and the octadecylamine/SA/APT composite system performed optimally at a contact angle of 167.54°. [Display omitted] [ABSTRACT FROM AUTHOR]

It is of great significance to study the effect of surfactants on the coal surface potential for effective dust suppression in mining faces. The effect of different concentrations of sodium dodecyl benzene sulfonate (SDBS) solution on the surface potential of the Zhaozhuang coal was measured by atomic force microscopy (AFM). The experimental results show that the SDBS solution has significant influence on the surface potential of the Zhaozhuang coal. The electrical characteristics of the coal surface at the nanometer scale are different from those of macroscopic or the mesoscopic level. The surface potential of coal is basically a normal distribution, showing certain electrical characteristics. The mean value of the surface potential of the Zhaozhuang coal is increased with the increase in concentration of the SDBS solution; when the concentration of the SDBS solution is 0.3%, the mean value of surface potential is 5.59 mv, which is about two times of the mean value of the surface potential without SDBS solution added. With the increase of the concentration of the SDBS solution, the maximum value of the surface potential of the Zhaozhuang coal increases, and the minimum value decreases. It shows that the SDBS solution has a significant effect on the potential distribution law and the magnitude of the coal surface. Subsequently, on the basis of the constructed Zhaozhuang coal macromolecule model, xtb and Multiwfn simulation software were used to calculate the molecular surface electrostatic potential value and electron density value of the Zhaozhuang coal molecules after adding water molecules. The variation law for the electrostatic potential surface of the molecule was obtained after adding numbers of water molecules to the surface of the coal molecule. The simulation results show that the area proportion of absolute molecular surface electrostatic potential greater than 10 kcal/mol is increased with the growth in the number of water molecules, while the area proportion of absolute molecular surface electrostatic potential less than 10 kcal/mol is decreased. Because of the free state O─H bond polarity of water molecules, the charges on the molecular surface are rearranged in order to change the electron density on the surface of coal molecules, which affects the overall electrostatic potential of the configuration. [ABSTRACT FROM AUTHOR]

Due to its better energy storage density and lower costs for storage, cryo-compressed hydrogen (CcH2) storage provides a wide range of research potential. Based on the grid theory, The type III CcH2 storage cylinder's layup scheme is created using the working environment for on-board hydrogen storage. The failure of the composite layer of gas cylinders was determined using the maximum stress criterion, and hydrodynamic bursting tests on small-volume gas cylinders were utilized to confirm that the design method was appropriate. The innermost layer of the ring winding is where the largest fiber stress is found, according to simulation studies. The load-bearing capacity of the cylinder is improved and can reach 115.1 MPa with layers in the order of [ 90 / ± 11.8 / 90 ]. The equivalent stress and fiber stress ratio of the cylinder continuously drop as the autofrettage pressure rises, while the cylinder's fatigue life gradually lengthens. • A program for designing hydrogen storage cylinders under cryo-compressed situation. • Stress analysis of each component of the cryogenic hydrogen storage cylinder. B • Urst failure of hydrogen storage cylinders and experimental validation. • Layup order's impact on the durability of cryogenic hydrogen storage cylinders. • Autofrettage pressure's impact on hydrogen storage cylinder fatigue performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • The degree of polymerization significantly affects the interaction of PEO with the surface. • Surface type has a bigger impact on water adsorption than polymer type but less than DP. • The interaction between PAM and the surface is strongly influenced by temperature. • The adsorption of PEO on surfaces depends mainly on the chain's deformation. • For XG-TDI and GG-HDI systems, van der Waals has the most impact on the interaction. Hydrophobic surfaces and polymer additives are both desirable for effectively reducing drag when carrying fluids, and the synergy of these two has naturally attracted a great deal of attention. The interaction between a polyurethane surface with different raw material compositions and drag-reducing polymers such as polyacrylamide (PAM), polyethylene oxide (PEO), xanthan gum (XG), and guar gum (GG) was investigated using molecular simulation methods such as molecular dynamics and Monte Carlo. The effects of polymerization degree (DP), temperature, and water molecule adsorption on the interaction were further examined. The findings demonstrate that rigid polymers (XG and GG) have a higher capacity for adsorption on the polyurethane surface than do flexible polymers (PAM and PEO). Furthermore, the DP clearly affects the PEO interacts with surfaces. Under a fixed water molecule load, the influence of surface type on water molecule adsorption ability is greater than that of polymer type but weaker than that of DP. Temperature clearly influences the interaction of PAM and surfaces, whereas PEO has the opposite effect. Additionally, PEO's deformation energy contributes more to the adsorption energy than others, whereas PAM's adsorption energy is higher because its longer molecular chains occupy the adsorption site on the surface. [ABSTRACT FROM AUTHOR]

Underground coal is often subjected to periodic loads caused by mining stress. To determine the effect of cyclic load on mechanical properties of coal of different ranks and failure mechanisms, nanoindentation experiments and molecular dynamics (MD) simulations were used to study different rank coals. The results indicated that cyclic hardening occurred in all the coal matrices under cyclic loading. With the increase in coal rank, the change of the elastic modulus and the hardness, the energy dissipation rate, and the damage layer decreased, the cyclic hardening weakened, and the resistance of the six-membered ring structure increased. The plastic failure of the coal matrix was mainly connected with the bending and stretching of the bond, the dihedral angle twisting, and the out-of-plane bending vibration. The elastic deformation was correlated with the variation of the Coulomb force and the van der Waals force, the twisting and recuperation of the dihedral angle, and the out-of-plane bending vibration. With increasing coal rank, the effect of the elastic deformation of the Coulomb force weakened. When the coal rank exceeded a certain range, the influence of the plastic failure of the out-of-plane bending vibration was transformed into the elastic deformation, and the effect of the elastic deformation of the van der Waals force was transformed into the plastic failure. • The higher the coal rank is, the weaker the cyclic hardening. • Mechanical properties of coal are calculated by MD simulation and verified. • The resistance of the six-membered ring increased with increasing coal rank. • Failure mechanism of coal is revealed from the microscopic point of view. [ABSTRACT FROM AUTHOR]

[Display omitted] • The simulation system of bituminous coal-surfactant-water was established. • The wetting effects of surfactants were obtained by simulation and experiment. • The interaction was analyzed by molecular dynamics and quantum chemistry. • O and N in surfactants affect the regulation of bituminous coal wettability. The regulation of surfactant on the wettability of bituminous coal surface is influenced by its hydrophilic structure. Based on the water absorption simulation and contact angle experiment of bituminous coal under different surfactants, the wetting effect of different surfactants with different hydrophilic structures on bituminous coal was obtained. The mechanism of different surfactants at the coal-water interface was analyzed by molecular dynamics simulation. The frontier orbital distribution and surface electrostatic potential distribution of surfactants and bituminous coal molecules were calculated by quantum chemistry method. The results showed that the wetting effect of surfactants on bituminous coal was APG1214 > OA-12 > SDBS > DTAB. The structure of hydroxyl and amine oxide made surfactants more conducive to promoting the interaction between coal and water molecules. The more oxygen and nitrogen elements the hydrophilic structure contains, the more favorable the surfactant is to modulate the wettability of the bituminous coal surface. [ABSTRACT FROM AUTHOR]

• Hardness, elastic modulus and fracture toughness have a good linear relationship. • Minerals could strengthen the macro-mechanical properties of coal rock. • Six-membered ring structure plays an important role in deformation resistance. • Failure mechanism of coal by the load is revealed. It is of great significance to explore the mechanical properties and failure mechanism of different rank coals at the nanoscale for preventing mine dynamic disasters. X-ray diffraction (XRD), mercury intrusion, and nano-indentation were used to study the relationship between rank, microstructure and mechanical properties of different rank coals, and using Mori-Tanaka method to upgrade the scale. To reveal the failure mechanism of coal, the nanoindentation process was simulated through molecular dynamics (MD). The results indicated that with the increase in coal rank, the peak load, hardness, elastic modulus, resistance of the six-membered ring structure, fracture toughness, the aromatic layer interlayer spacing (d 002), positively proportional to lateral sizes (La), stacking height (Lc), and the number of aromatic layers (n) increased, while the plastic deformation, permeability, porosity, mineral content, and thickness of the damaged layer decreased. Minerals could strengthen the macro-mechanical properties of coal rock, while the pores weaken it. The load destroyed the bonds, angles, dihedral angles, and out-of-plane of coal macromolecules, which led to the plastic deformation of coal. And bonds and angles had the greatest influence on the failure of coal, followed by dihedral angles, and finally out-of-plane. [ABSTRACT FROM AUTHOR]

• Three-dimensional molecular model of carbon black was constructed. • Carbon black has a high degree of condensation polymerization. • Nonionic surfactants have the strongest interaction with the carbon black surface. • Molecular simulation can be used as a method to study the wettability of carbon black. An experiment and simulation study on the carbon black adsorption of surfactant were conducted to explore the adsorption mechanism to assist in the prediction and prevention of dust accidents. Elemental analysis, 13C solid nuclear magnetic resonance (13C-NMR), and X-ray photoelectron spectroscopy (XPS) were used to construct the model of the carbon black. Molecular dynamics (MD) and molecular mechanics (MM) were used to optimize the model of the carbon black, and the periodic boundary condition was added using the relationship between energy and density. The adsorption behavior of surfactants on the surface of carbon black molecules was studied using molecular dynamics simulation. In the molecular model of carbon black aromatic compounds mainly exist in the form of the benzene ring; aliphatic compounds mainly exist in the form of aliphatic side chains and cycloalkanes; oxygen atoms exist as carbonyl group, ether group, and carboxyl group; and nitrogen atoms exist as pyridine and pyrrole. The final density of the carbon black molecule model is 1.5 g/cm3. The molecular simulation results show that the nonionic surfactants have a better wetting effect on carbon black. Interaction between carbon black molecules and surfactants is caused by electrostatic force and van der Waals force, increasing the number of water molecules adsorbed by carbon black. The simulated adsorption results have a good predictive effect on the modification, removal, and dust control of carbon black. [ABSTRACT FROM AUTHOR]

There is a strong fluid-solid coupling effect during the process of coal seam pulse water infusion. Based on the basic principle of liquid-solid coupling, the dynamic damage evolution rule during coal seam pulse water infusion is simulated through secondary development of ABAQUS software. During this process the mathematical model of the strain accumulation model due to the periodic changes of pulse water pressure is embedded in SOIL module of ABAQUS software discussed in this paper, in order to obtain the dynamic damage evolution rule of coal seam around the pulse water infusion hole. It provides a new quantitative method of determining coal seam pulse water infusion parameters and location. The law of different parameters of pulse water infusion on the dynamic damage evolution of coal around the infusion hole is gotten. Numerical simulation results show that, during the process of coal seam high pressure pulse water infusion, the stress field and flow field are mutual influence and mutual restriction. The coupling of the stress and flow field have impact on the physical and mechanical properties of coal in front of the working face, these factors promote each other and prevent coal and gas outburst effectively. The coal damage quantity increases significantly with the water infusion time prolonging under constant water infusion pressure and frequency. The coal damage quantity increases significantly with the water infusion pressure increasing under constant water infusion time and frequency. The coal damage quantity increases significantly with the water infusion frequency increasing under constant water infusion pressure and time. So the pulse water infusion time needs to ensure a better effect of preventing coal and gas outburst is gotten. Meanwhile the pulse water infusion pressure needs to improve under the existing technical conditions. The frequency of pulse water infusion needs to improve under the existing technical conditions. This research results contribute to obtain accurate dynamic distribution law of damage fields around water infusion holes. It provides theoretical basis for optimizing pulse water infusion in technological parameters design and raising water infusion effect. [ABSTRACT FROM AUTHOR]

• Wetting mechanism of SDBS on different rank coal is analyzed. • Surface free energy affects hydration film thickness and thus changes the wettability. • The SEF of different-rank coal increased and then decreased with adsorbed SDBS increased. • SDBS had a greater effect on high-rank coal samples' wettability than low-rank. • The wettability of SDBS on high-rank coal is influenced by Van der Waals forces. Surfactants to improve the wetting ability of water sprays are considered an effective method of suppressing coal dust. Sodium dodecyl benzene sulfonate (SDBS) was used to understand the wetting mechanisms of an anionic surfactant on coals of different ranks. Atomic force microscopy (AFM) experiments and molecular dynamics simulations were used to investigate the surface free energy and hydration film. The analysis showed that the hydration film thicknesses obtained by both the experiment and simulation increase and then decrease with increasing SDBS concentration, and the high-rank coal had a thicker hydration film than the low-rank coal. The electrostatic potential distribution, hydrogen bonding, Mulliken charge, and interface formation energy were analyzed to illustrate the wetting mechanism. It was confirmed that coal's wettability is mostly determined by the electrophilicity of hydrogen atoms in oxygen-containing groups, and for high-rank coal, van der Waals forces gradually become the dominant forces in the wetting of the coal by SDBS. In conclusion, surface free energy theory by MD simulation proved to be a reasonable way to reveal the wetting mechanism of surfactants on coal, and the enhancement effect of SDBS on the wettability of high-rank coal is stronger than that of low-rank coal, which contributes to the development of surfactants for practical engineering applications. [ABSTRACT FROM AUTHOR]

The coalbed methane need to be exploited before coal mining through gas drainage, in order to obtain the dual purposes of lower coal mine accident rate and transfer gas into treasure. There is a strong fluid-solid coupling effect during the gas drainage processing. The seepage law of coal from Guzhuang mine of China at different gas pressure is tested, and its klingberg coefficients is obtained by curve fitting method. Based on the klingberg effect, the liquid-solid coupling effect of coal and gas is simulated through secondary development of ABAQUS software in this paper, in order to obtain the dynamic variation rule of gas pressure field and seepage field around the gas drainage hole. It provides a new quantitative method of determining gas drainage parameters and location. Numerical simulation results show that, during the processing of gas drainage, the stress field and seepage field are mutual influence and restriction, the gas pressure around the drainage holes is reduced and the coal seam stress relief, permeability increases, these play a prominent role in the effective prevention of coal and gas outburst. Research results contribute to obtain accurate dynamic distribution law of the stress and seepage fields around gas drainage holes. It provides theoretical basis for optimizing gas drainage technology and raising gas drainage effect. Gas drainage generally defined as the high concentration gas is extracted using gas pumps or other drainage device, and high density gas is discharged into the ground or the total return airway through the isolated pipe network [1]. The gas drainage is an effective measure for preventing coal and gas outburst, gas explosions and gas emission. The dual purpose with lower coal mine accident rate and transfer gas into treasure can be gotten. At present, China's coalbed methane exploitation is lagging behind. Theoretical research and effective analysis method about gas drainage technology design are rare [2-8]. As the gas pressure changes, the permeability of the coal body significantly changes due to klingberg effect during the gas drainage process. It has important impact on the gas seepage. So the fluid-solid coupling effect has important impact on gas seepage during gas drainage process. The fluid-solid coupling law of gas and coal is analyzed using the ABAQUS software during gas drainage process. The research result of coupling effect of gas pressure field and stress field has important theoretical value and practical significance on revealing the mechanism of gas drainage preventing coal and gas outburst and field implementation of the gas drainage for preventing coal and gas outburst. [ABSTRACT FROM AUTHOR]

[Display omitted] • The simulation model of coal-surfactant-water adsorption is given. • Nonionic surfactants are more likely to accumulate on the surface of coal molecules and have a greater impact on the wettability of the coal surface. • The middle position of the benzene ring structure in coal is the best adsorption site for the hydrophobic tail of the surfactant. • The phenomenon of "reverse adsorption" between nonionic surfactants and low metamorphic coal is caused by hydrogen bonding. To study the effect of different surfactants on the wettability of coal surface, the adsorption simulation of different coal-surfactant-water model systems was carried out by using materials Studio 8.0 molecular simulation software. Combined with the contact angle experiments between different surfactants and coal samples, the effect law of different surfactants on the wettability of three coal samples was obtained. The adsorption simulation results were analyzed from the aspects of adsorption spacing, adsorption sites and "reverse adsorption" phenomenon, and the mechanism of the influence of different surfactants on the wettability of coal surface was revealed from a microscopic point of view. The research results show that: the higher the degree of coal metamorphism, the lower the water absorption and the worse the wettability of coal. Anionic surfactant SDBS has better effect on improving the wettability of Hami (HM) coal with low metamorphic degree, while nonionic surfactant AEO 9 has better effect on improving the wettability of Yuwu (YW) and Tunliu (TL) coal with high metamorphic degree. By comparing intermolecular distances, it is shown that nonionic surfactants are more likely to aggregate on the surface of coal molecules and have a greater effect on the wettability of the coal surface. The middle position of the benzene ring structure of coal is the best adsorption site for the hydrophobic tail of the surfactant. By calculating the adsorption energy of different simulation systems, it is confirmed that the phenomenon of "reverse adsorption" between nonionic surfactants and low metamorphic coal is caused by hydrogen bonding. The results of the study provide a theoretical basis for the effective application of different surfactants in coal dust control. [ABSTRACT FROM AUTHOR]

• The real coal molecular models at different ranks were constructed by relevant experiments. • Combined GCMC and DFT methods were used to reveal the adsorption mechanism of coal molecules at different ranks. • The aromatic structure in the coal molecules has stronger adsorption capacity than oxygen functional groups. • The adsorption capacity of the adsorption sites in the aromatic structure is ranked as T > B > C. • Coal molecules change the structure and chargeability of the adsorbed methane molecules. The adsorption mechanism of methane molecules and coal molecules at different ranks is of significant practical and theoretical importance in prevention gas disaster and methane storage. In this paper, four coal samples at different ranks were selected for experiments. The real coal molecules at different ranks were constructed. The relationship between the coal components and the gas adsorption capacity was analyzed. The adsorption mechanism was studied by performing combined Grand Canonical Monte Carlo(GCMC) and Density Functional Theory (DFT)simulation at temperatures of 298 K and at pressure range of 0–100 bar. The simulation results display a good agreement with the experimental results. In the process of methane adsorption simulation, methane molecules are preferentially adsorbed on the edge of the unit cell and then adsorbed inside the coal molecules. The methane molecules in the Up orientation have stronger adsorption capacity then Down orientation. The adsorption capacity order is as follows: aromatic structure > oxygen functional groups. In the aromatic structure, the adsorption capacity of adsorption sites is ranked as T > B > C. In the oxygen functional groups, the adsorption of methane by the coal molecule is caused by both the adsorption position and the adsorption direction. Under the influence of coal molecules, the structure and the Mulliken charge of methane molecules change significantly during the adsorption simulation. The adsorption forces between the coal molecules and methane molecules are mainly induced force, dispersion force, orientaion force and electrostatic force. This study enables us to better understand the adsorption mechanism of coal molecules at different ranks. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) must be suppressed owing to its adverse effect on high-power fiber lasers. We propose a bending-sensitive multi-ring fiber composed of three parts: a core, multiple high-refractive-index rings, and a cladding. Appropriate bending of the fiber produces a high loss of the first-order Raman Stokes wavelength at 1114 nm and low loss of the signal wavelength at 1064 nm, thus enabling the signal light to be confined to the core while maintaining single-mode transmission. This principle relies on the resonant coupling between the core and ring modes. Numerical analysis indicated that the loss ratio of the fundamental mode could reach 2650.041 by optimizing the structural parameters. Moreover, when the three-ring fiber was subjected to a bending radius of 6 cm, a bend-induced loss of the Raman wavelength reached 11.315 dB/m , which effectively suppressed the first Stokes SRS generation. [ABSTRACT FROM AUTHOR]

Self-developed electric explosion technology (EET) equipment is used to conduct rock-breaking experiments. A high-speed camera is used to record the expansion of cracks during rock breaking. The Hilbert-Huang transform (HHT) is used to analyze the vibration signals, which reflected the action pattern of shock waves (SWs). Hilbert marginal spectrums, instantaneous energy spectrums, and three-dimensional Hilbert spectrums are used to illustrate the distribution and variation of energy in the time and frequency domains. The experimental results show that SWs energy of 0 to 500 Hz accounts for more than 72% of the total energy, and energy of 0 to 2500 Hz accounts for more than 90% of the total. Energy of SWs has a high base value at the onset of discharge. Energy drops rapidly as discharge time continues. When rocks fracture, there will be obvious instability phenomena, including transfer of energy in frequency, reduction of energy attenuation rate, and reduction of the derivative waves effect. [Display omitted] • Self-developed EET system implements large-scale rock fracture experiments • Research analysis of the instability characteristics of rocks fractured during EET. • Research uses HHT to analyze the energy distribution characteristics of SW. [ABSTRACT FROM AUTHOR]

Eleven coal samples of different metamorphism are studied with regard to their pore structures. Both low-pressure nitrogen gas adsorption (LP-N 2 GA) and scanning electron microscopy (SEM) were performed. The use of these techniques allows us to gain clearer insight into the nature of the pore structure including the pore volume, specific area, pore size distribution (PSD) and pore shape. The LP-N 2 GA isotherms demonstrate strong differences in gas adsorption capacity between the coal samples studied, consistent with variability in specific surface area (SSA) of the samples. Pore geometry of coals with different metamorphism varies a lot, indicative of heterogeneity on coal surface, which was verified with SEM observation. Adsorption analysis revealed that mesopore size distributions are multi-modal, whereas, the micropore structure of the samples tested appears to be unimodal, with a major peak between 1.6 and 2.0 nm. The influence of coal rank on pore structure was also analyzed. The U-shape relationship between mesopore SSA and V daf is observed, demonstrating that the number of mesopores within the lower rank coals ( V daf > 15%) decreases with increasing coal rank and the coalification mainly affects the mesopore structure. For the higher rank coals with V daf < 15%, as the coalification effect increases, the mesopore size diminishes and the number of micropores ascends. Smaller mesopores and micropores gradually become the dominant roles. This phenomenon is due to the effect of intensive compaction within the coal bulk. The combination of LP-N 2 GA and SEM techniques gives a better understanding of pore characteristics in coal. The research results will provide guidance for the gas control in coal mines. [ABSTRACT FROM AUTHOR]

Gas is one of the most important factors which causes coal and gas outburst and can influence the mechanical characteristics of coal. Coal itself is a kind of elastic carbonaceous material which can swell and shrink under the influence of gas adsorption and desorption. Solid deformations influence the porosity of coal which also changes its adsorption and desorption capability. Gas pressure due to gas adsorption in porous materials is the cause of elastic deformation of coal, which can be assessed by direct experimental measurements. In this paper, briquette coal samples are made with different sizes of coal particles and the deformations are tested during the process of gas adsorption and desorption in samples under different gas pressures. The results show that coal swells during gas adsorption and shrinks during desorption. Deformation of different coal samples under different gas pressures is variable. It is further observed that deformation of coal is proportional to gas pressure and particle size. Also, deformation is not recoverable and residual deformation develops. The relationship between residual deformation and gas pressure is derived. This study helps to reveal the damage mechanism of pore gas in cola mass. [ABSTRACT FROM PUBLISHER]

Outburst simulation experiments facilitate understanding coal and gas outburst in underground mining. With the help of the mid-scale simulation system, a model based on similitude principle, coal seam sandwiched by roof and floor, was constructed to conduct an outburst experiment. It had a three-dimensional size of 1500 mm × 600 mm × 1000 mm with 0.5 MPa gas pressure. The experimental procedures include specimen preparation, moulding, sealing, gas charging and adsorption, and completion. The outburst process was investigated by analyzing the gas pressure variation, temperature variation, outburst propagation velocity, particle size of outburst coal and energy transformation. During the experiment, each gas charging was accompanied with gas pressure or temperature fluctuation because of coal behavior of gas adsorption-desorption. The outburst propagation velocity was 17.2 m/s, obtained by a mass-weighted calculation of velocities of outburst coal. The small-size coal particles have a higher desorption rate and tend to participate in outburst process. According to energy conservation law, the energy forms of the outburst included elastic strain energy (Ee), gas expansion energy (Ep), internal energy of coal (ΔU), breakage work (W1), throwing out work (W2) and gas-flow loss energy (ΔE), and each was calculated respectively. Gas potential energy, including gas expansion energy and internal energy of coal, registered a larger percent and was far greater than the strain energy. And it can be the main factor influencing the occurrence of low-threshold outburst. The experimental system provides a feasible way to study the initiation and evolution of coal and gas outbursts. [ABSTRACT FROM AUTHOR]