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Understand the microscopic mechanism of supercritical water catalytic gasification is of great significance for more efficient and convenient utilization of biomass energy. In this work, Pt and Ni nano-particles (NPs) were used as catalysts to accelerate the SCWG of guaiac-based lignin dimer with γ -O-4 linkages for the first time, and the SCWG processes at different conditions were simulated by reaction molecular dynamics simulation to understand the degradation mechanism and the path of gas generation. The simulation results indicate that PtNPs and NiNPs apparently reduce the temperature at which the gasification reaction can take place and the by-products of γ -O-4 lignin by increasing the degradation rate into monomer, accelerating the aromatic ring opening, and adsorbing CO, CO 2 and CH 4. Compared with NiNPs, the synergy of PtNPs and SCWG shows more excellent properties. • Microscopic synergy mechanism of catalytic-SCWG is analyzed. • Nano-catalyst accelerates SCWG of lignin and reduces the reaction temperature. • PtNPs gives greater improvement on SCWG than NiNPs. • The SCW/lignin ratio has important influence on the efficiency of H2 generation. [ABSTRACT FROM AUTHOR]

High performance fibers with high strength and toughness have great potential in composites, but contradiction between tensile strength and elongation at break makes the preparation to become a current challenge. Herein, an asymmetric structure of more flexible diamine, 3,4′‐diaminodiphenyl ether (3,4′‐ODA), is introduced into heterocyclic aramid (PBIA) fibers to replace rigid symmetric p‐phenylenediamine (PDA). By studying the properties of copolymer (mPEBA) fibers with different ratios of diamine, it is found that the mPEBA fiber reached the optimal mechanical properties with the 30% content of 3,4′‐ODA. Compared with homopolymerized heterocyclic aramid fibers, the tensile strength and elongation at break of mPEBA fiber are improved by 26.2% and 38.7%, respectively. Results of X‐ray diffraction show that the introduction of 3,4′‐ODA structure can increase stretchability of mPEBA fibers, improving the orientation degree during hot‐drawing. Molecular dynamics simulations confirm that 3,4′‐ODA structure undergoes a conformation transformation to form a straightened chain during hot‐drawing, while symmetrical 4,4′‐diaminodiphenyl ether (4,4′‐ODA) cannot form the same conformation. The misplaced‐nunchaku structure is formed based on the special meta‐para position of 3,4′‐ODA, achieving the synergy of high strength and high toughness. [ABSTRACT FROM AUTHOR]

Understanding the micro-mechanism of lignin gasification in supercritical water is meaningful for improving the energy conversion efficiency of biomass. In this work, the molecular model of guaiacyl dimer lignin with γ-O-4 linkages is built and the gasification processes of it in supercritical water at 9 different temperatures between 2000 K and 6000 K are studied by ReaxFF molecular dynamics simulations for the first time. The cleavage mechanism of γ-O-4 lignin and the generation pathways of gases were analyzed. During the gasification process of γ-O-4 lignin, H 2 and CO are abundantly generated, while supercritical water contributes the most H and O molecules for them. Temperature are found to play important role in the products and rate of the cleavage of lignin. • Molecular model of guaiacyl dimer lignin with γ-O-4 linkages is built. • Gasification process of lignin in supercritical water is studied by ReaxFF MD. • Effects of temperature and supercritical water on lignin cleavage is analyzed. • Generation pathways of the main gaseous products are obtained. [ABSTRACT FROM AUTHOR]

• Thermophysical properties and condensation process of R1233zd(E) were simulated. • Phase transition rate of R1233zd(E) increase as p sim increases or t sim decreases. • E vdw gives greatest contribution to e p change during phase change process. • R1233zd(E) has faster condensation rate than R1234ze(E), R1243zf and R1234yf. R1233zd(E) is one promising alternative refrigerant with excellent environmental-friendly performance. In this paper, the molecular dynamics simulation method was used to study the density, heat capacity and homogeneous condensation nucleation process of R1233zd(E) from a superheated state to different supercooled states aiming to provide information for its application. The higher condensation pressure and lower condensation temperature was found to be favorable to increase condensation rate of R1233zd(E). During the nucleation process, the molecular distribution of R1233zd(E) becomes uneven; meanwhile, the potential energy has a sharp drop which is mostly caused by the drop of van der Waals energy. The faster condensation rate of R1233zd(E) compared to other three HFOs R1234ze(E), R1243zf and R1234yf is helpful to improve refrigeration efficiency. [ABSTRACT FROM AUTHOR]

This paper presents structure, thermal expansion coefficient and phase stability of La 2 (Zr 0.7 Ce 0.3 ) 2 O 7 (LZ7C3) ceramic by both theoretical and experimental results. It was found out that LZ7C3 powders had a pyrochlore structure after being heat-treated at temperatures higher than 1473 K or higher according to XRD and TEM results. The calculated average thermal expansion coefficient (TEC) was 7.12 × 10 −6  K −1 , which is a little smaller than experiment result, but changes of calculated average TECs of LZ, YSZ and LZ7C3 had the same trend with experimental results. Finally, the radial distribution function (RDF) was calculated to study the phase stability of LZ7C3. [ABSTRACT FROM AUTHOR]

Waste lignin and plastic can be converted into useful syngas by co-gasified in supercritical liquids. In this work, lignin with β -O-4 linkages and two kinds of common plastics, polyethylene and polypropylene, were simulated in the process of co-gasification. The processes in supercritical water (SCW) or supercritical carbon dioxide (SCCO 2) environment at different temperatures and ratios of reactants were studied comparatively using ReaxFF molecular dynamics simulations. The composition of products has been analyzed, the co-gasification synergistic effect has been explored, and the reaction mechanisms were provided and compared. The addition of plastic increased the production of H 2 in both the SCW and SCCO 2 systems The effect of adding plastics on the initial pyrolysis of lignin in SCW was greater than that in SCCO 2 , resulting in the production of more H 2 and CH 4 and less CO in the SCW system. • Recycle waste lignin and plastics to generate usable energy products. • Revealed and compared the evolution of co-gasification. • Temperature and ratio of lignin to plastics apparently effect the gasification. [ABSTRACT FROM AUTHOR]

Abundant renewable lignin resources have attracted increasing attention. Supercritical carbon dioxide exhibits excellent catalytic gasification properties. In this study, a molecular model for softwood lignin was established as a reactant. The ReaxFF molecular dynamics simulation method was used to simulate the gasification of softwood lignin in a supercritical carbon dioxide environment with platinum nanoparticles as catalysts. A slow temperature increase (80 K/ps) was used, and the system was studied at a constant temperature of 1700 K. The cleavage of different bonds at the initial stage of the reaction was studied, and the different gasification productions under the action of the catalyst in supercritical carbon dioxide were analysed and compared with those under non-catalyst conditions. The results showed that with the addition of the catalyst, the amount of CO 2 cracking increased, the number of H 2 and CO molecules produced increased, and the reaction rate increased. • Revealed the evolution of lignin in supercritical carbon dioxide gasification. • PtNPs apparently accelerated the gasification. • Increased the production of H 2 and CO. • PtNPs adsorbed CO. [ABSTRACT FROM AUTHOR]

• Structure and flow of IL with water and electric field in nanochannel are studied. • Water and electric field can weaken the stratification effect of density. • Adding water improves flow velocity of [EMIM][BF 4 ] and changes its flow state. • Electric field in flow direction can accelerate the flow of [EMIM][BF 4 ]. Developing regulation method for the structure and flow of ionic liquids (ILs) in the nanochannel is of great importance to their application in nanodevice. For this purpose, the density and charge distribution and the flow behavior of [EMIM][BF 4 ] blended with water as diluent and imposed electric field in nanochannel are studied using molecular dynamic simulation method in this work. The results reveal that the addition of water can weaken the stratification effect of density and charge distribution while doesn't significantly change the micro-structure of [EMIM][BF 4 ], while the electric field in different directions results different influence on the stratification effect. Addition of water can make a significant improvement in the flow velocity of [EMIM][BF 4 ] and change its flow state. Imposing electric field in flow direction can accelerate the flow, but imposing electric field perpendicular to nanochannel handles the flow. [ABSTRACT FROM AUTHOR]

Fluorinated graphene contains F atoms with high levels of chemical activity, and the application of fluorinated graphene in energetic materials may greatly contribute to the progress of combustion reactions. However, there is a lack of research on the thermal properties of fluorinated graphene and its application on nitrate esters. In this paper, theoretical calculations and experiments were used to study the thermal properties of fluorinated graphene and its application on nitrate esters. The anaerobicity and poor thermal stability of fluorinated graphene were proved by ab initio molecular dynamics (AIMD) calculations and TG-DSC experiments. The ester weakening effect of fluorinated graphene on nitroglycerin was determined via wavefunction analysis, with the greater the fluorination degree, the stronger the ester weakening effect. The existence of fluorinated graphene can significantly increase the heat dissipation of the composites, which was concluded by TG-DSC experiments and TG-DSC-MS-FTIR. The research in this article provides an important reference for the application of fluorinated graphene in energetic materials. [ABSTRACT FROM AUTHOR]

• Structure and transport of [EMIM][BF 4 ] and H 2 O in asymmetric nanochannel are studied. • Effect of nanochannel height, coating graphene and driving pressure are analyzed. • Coating graphene obviously improves transport of [EMIM][BF 4 ] and H 2 O in nanochannel. The transport of ionic liquids (ILs) in nanochannel is greatly restricted, and facilitating transport of ILs is of great significance to their applications in gas separation, battery and supercapacitor, etc. In this work, we use molecular dynamic simulation to investigate the molecular structure, charge distribution, diffusion behavior and flow characteristics of [EMIM][BF 4 ] confined in asymmetric graphene-coated silica nanochannel to provide information for guiding the fabricate of nanodevice, and analyze the influence of nanochannel height, coating graphene and driving pressure. Water also studied as a comparison. The results indicate that [EMIM][BF 4 ] and water confined in silica nanochannel present layered structure, and coating graphene on the wall surface of silica nanochannel can enhance the layering effect, and uniformize the charge distribution and reduce the diffusion coefficient. [EMIM][BF 4 ] presents different flow states at varying nanochannel height, including Poiseuille flow and partial plunger flow, but water only presents Poiseuille flow. Coating graphene on wall surface of silica nanochannel results obvious positive slippage on the wall surface and the fast transport in nanochannel. [ABSTRACT FROM AUTHOR]

Ammonia nitrogen and phenol are typical inorganic and organic pollutants in the coal chemical wastewater, respectively. In this study, the adsorption characteristics of ammonia nitrogen and phenol on lignite were investigated through experimental and molecular dynamics simulations. The results show that the adsorption of ammonia nitrogen was carried out via ion exchange, which was significantly faster than the adsorption of phenol driven by the π–π interaction. In the binary adsorption, the surface electronegativity of lignite decreased with the adsorption of ammonia nitrogen thereby promoting the adsorption of phenol. However, the extent of ammonia nitrogen adsorption was slightly reduced in the presence of phenol. Molecular dynamics simulation results indicated that the adsorption of phenol molecules on the lignite surface was closer than that of ammonium ion. The addition of ammonium ions could enhance the adsorption of phenol molecules on the lignite surface. The simulation results were well consistent with the experimental findings. This study indicates lignite has a promising potential in coal chemical wastewater adsorption pretreatment. [Display omitted] • Lignite adsorption was based on mesopores and oxygen functional groups. • The adsorption rate of NH 4 +-N on lignite was faster than that of phenol. • The adsorption quantity of phenol on lignite was increased by NH 4 +-N. • MD Simulation provided atomic-scale details of adsorption. [ABSTRACT FROM AUTHOR]

Understanding of the interaction and thermophysical properties of HFO and ionic liquid mixture at the micro level is helpful for the molecular design of the new working pair of HFO + ionic liquid for absorption refrigeration. In this work, the densities, viscosities, thermal conductivities and diffusion coefficients of HFO-1234yf and [bmim][Tf 2 N] are firstly calculated using molecular dynamics simulation method and compared to the results in literature in order to verify the reliability of our method. Then, the density, energy, diffusion coefficient and radial distribution function of the liquid mixture of HFO-1234yf and [bmim][Tf 2 N] are calculated and analyzed. The dissolution of HFO-1234yf in ionic liquid is found to increase the diffusion coefficients of [bmim] and [Tf 2 N]. [bmim] and [Tf 2 N] both play important role in the absorption of HFO-1234yf. • Diffusion and interaction of HFO-1234yf/[bmim][Tf 2 N] mixture are studied using MD. • Dissolution of HFO-1234yf increases diffusion coefficient of [bmim] and [Tf 2 N]. • Coulomb energy gives greatest contribution to the reduction of potential energy. • [bmim] and [Tf 2 N] both play important role in the absorption of HFO-1234yf. [ABSTRACT FROM AUTHOR]

Hydrofluoroolefins are regarded as the most promising alternative refrigerant for hydrofluorocarbons because of their better environmental performance. Understanding the condensation process of refrigerant is of great significance for the design of the condenser. In this work, the vapor condensation processes of 3,3,3-trifluoropropene (R1243zf), trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) and 2,3,3,3-tetrafluoropropene (R1234yf) from (343.15 K, 385 kPa) to eight condensation states (283.15 K, 1 MPa; 283.15 K, 1.5 MPa; 283.15 K, 2 MPa; 283.15 K, 2.5 MPa; 283.15 K, 3 MPa; 268.15 K, 1 MPa; 273.15 K, 1 MPa; 278.15 K, 1 MPa) were investigated by molecular dynamics simulation. The densities and isobaric heat capacities of R1243zf, R1234ze(E) and R1234yf were simulated and compared with experimental data to verify the reliability of our simulation method. The effects of the condensation temperature, the condensation pressure, the saturation temperature and the saturation pressure on the phase transition rate were analyzed. The variations of the potential energies and radial density distribution functions of R1243zf, R1234ze(E) and R1234yf were simulated to get insight into the condensation process on a micro-level. • Condensation process of HFO was studied by molecular dynamics simulation. • Phase transition rate of HFO increases as p sim increases or T sim decreases. • Variations of potential energy and RDF of HFO during condensation were analyzed. • Condensation of HFO does not affect their intramolecular structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • The dynamic adsorption process were studied by combining MD simulation and quantum chemistry. • The adsorption mechanisms of NH 4 + and phenol molecules on the lignite surface were compared. • The main interaction between NH 4 + and lignite was hydrogen bonding. • There were π-π stacking and hydrogen bonding in binding interaction of phenol and lignite. • Electrostatic effects played an important role in the intermolecular binding. To elucidate the adsorption mechanisms between the lignite and typical fractions from the wastewater, the microscopic adsorption behavior of ammonia nitrogen and phenol on the lignite surface was investigated by molecular dynamics simulation. Meanwhile, the interaction strength and properties of lignite structural units with ammonia nitrogen and phenol were examined by combining quantum chemical calculations and wave function analysis. The results showed that a small amount of NH 4 + was adsorbed in the lignite structure, but most ions remained in the aqueous phase. Compared with NH 4 +, phenol was adsorbed more easily on the lignite surface. In addition to O···H hydrogen bond, there were cation-π interactions between NH 4 + and lignite structural units. The main interactions between phenol and lignite structural units include π-π stacking and hydrogen bonding, as well as a small amount of van der Waals (vdW) interactions. The total hydrogen bond energy of the lignite structural unit to the four conformations of NH 4 + as a percentage of the total binding energy was 72.34, 82.64, 51.00, and 51.02 %, respectively, while that for phenol was 40.94, 53.42, 62.18 and 73.31 %, respectively. And the electrostatic effects played a major role in the binding interaction of the NH 4 + and lignite structural units, while the dispersion effects and electrostatic effects dominated the binding interaction of the phenol and lignite structural units. In the gas phase, the maximum binding energy between NH 4 + and lignite structural units was higher than that between phenol and lignite. However, the binding energy between phenol and lignite structural units was higher in aqueous solution, which was consistent with the result that phenol was more easily adsorbed by lignite in molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

• Thermal transport properties of pyrochlore-type (P-type) and fluorite-type (F-type) A 2 B 2 O 7 were investigated. • The thermal conductivity of F-type A 2 B 2 O 7 is merely 30%∼50% (0.83∼3.37 W•m1K-1) of that of P-type ones. • Y 2 B 2 O 7 and YbB 2 O 7 have the lowest thermal conductivity in the F-type A 2 B 2 O 7 family. • The thermal conductivity of materials can be significantly reduced by enhancing the fluctuation of interatomic bonding. Pyrochlore-type (P-type) and fluorite-type (F-type) rare-earth A 2 B 2 O 7 -type oxides attract extensive interest in engineering applications in which ultralow thermal conductivity is strongly required for improving energy-utilization efficiency and thermal management. Herein, thermal transport properties of P-type and F-type A 2 B 2 O 7 (A = Y , La, Nd, Sm, Gd, Yb; B = Zr, Ce, Hf) was systematically investigated using molecular dynamics. The thermal conductivity of F-type structures was found to be 0.83∼@3.37 W·m-1K-1, which is 30%∼50% of that of P-type structures. Such an low thermal conductivity is due to the stronger phonon scattering in F-type structures resulting from the inhomogeneous interatomic bonding. It was also found that the thermal conductivities of F-type A 2 B 2 O 7 being less dependent on temperature and closer to the theoretical minimum values due to the presence of amorphous-like phonon modes. Finally, we identified the optimal compositions in F-type A 2 B 2 O 7 family for achieving lowest thermal conductivity at high temperatures. This study suggests that enhancing the inhomogeneity of interatomic bonding can enable low thermal conductivity in simple-composition materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The surface chain cleavage behavior of PBIA fiber induced by direct fluorination was reported based on the analysis of physical and chemical changes on the fiber surface. The chain cleavage product was obtained to evaluate the chemical reaction during the fluorination process, and its impact on composites performance was also involved. DSC, FTIR spectra, UV–vis absorption spectra and H 1 NMR were utilized to analyze the chemical structure and composition of the chain cleavage product. The results show gaseous fluorine is most likely to attack the benzimidazole and amide bond in PBIA unit, which was also demonstrated by molecular simulation. Owing to the polar groups contained in chain cleavage products, the wettability of epoxy resin to fiber has been improved, leading to an 11.5% increase of adhesive strength of fiber-epoxy composite. [ABSTRACT FROM AUTHOR]

• The adsorption amounts of CO 2 are greater than those of H 2. • The oxygen atom of CO 2 is easily adsorbed onto the Ca ion of calcite. • CO 2 is dominant in the adsorption phase, while H 2 is dominant in the bulk phase. • The studied diffusion coefficients of H 2 are greater than those of CO 2. • The calcite has greater affinity for CO 2 than for H 2. The adsorption and diffusion of gases in porous media are fundamental phenomena that find widespread application in the energy and chemical industries. In this study, we used Grand Canonical Monte Carlo and molecular dynamics simulation methods to evaluate the adsorption and diffusion properties of CO 2 and H 2 in the calcite silt-like pores. We report the influence of pressure, pore size, and temperature on adsorption isotherms (i.e., total, absolute, and excess) and diffusion coefficients (i.e., self-diffusion, Fick transport diffusion, and Maxwell-Stefan diffusion). The results reveal a greater CO 2 adsorption capacity compared to H 2 and the easy absorption of the oxygen atoms of CO 2 onto the surface of calcite. The adsorption capacities of CO 2 and H 2 increased together with the pressure, and the pore size had little effect on the absolute adsorption capacity and density distribution of the pure compounds. The interaction energy between calcite and CO 2 /H 2 showed that the calcite had greater affinity for CO 2 than for H 2. The CO 2 diffusion coefficients were smaller than those of H 2. The diffusion coefficients of CO 2 and the mutual diffusion coefficients of the gas mixture increased with increasing pressure before stabilizing. In contrast, the diffusion coefficients of H 2 decreased with an increase in pressure. [ABSTRACT FROM AUTHOR]

The adsorption of hydrogen sulfide in gas reservoir cores is important to natural gas industry for predicting the sulfur content. Here, the adsorption of hydrogen sulfide in the calcite pore is investigated using molecular simulations. The results show that the absolute adsorption amount of H 2 S increases with the increasing of the pressure. However, the absolute adsorption amount decreases with the increasing of temperature. The adsorption capacity of H 2 S on the calcite surface can be well described by the combination of Langmuir equation and Clausius-Clapeyron equation. In order to investigate the effect of hydrogen bond on adsorption, a method of computing the hydrogen bond of H 2 S is proposed. The number of the average hydrogen bond per H 2 S molecules increases with the increasing of pressure. Furthermore, the existence of calcite surface will affect the distribution of hydrogen bond. This will order the structures of H 2 S molecules near the calcite surface and break the hydrogen bonds. • A method of calculating the hydrogen bond of H 2 S is proposed. • Langmuir equation and Clausius-Clapeyron equation are applied to describe adsorption capacity of H 2 S. • GCMC and MD simulations are combined to study the adsorption of H 2 S. • The existence of calcite surface will affect the distribution of hydrogen bond. [ABSTRACT FROM AUTHOR]