WETTING SIMULATIONS OF HIGH-PERFORMANCE POLYMER RESINS ON CARBON NANOTUBE SURFACES USING MOLECULAR DYNAMICS

There is a wide application of carbon nanotube (CNT) based composite materials for structural applications in the aerospace industry. CNT composites are often manufactured with high performance polymer resins as a matrix. Resin wettability with specific reinforcement types is a key parameter in manufacturing CNT composites. Wettability of a liquid resin and reinforcement combination is often measured and quantified by the contact angle. Various experimental methods have been developed to determine the contact angle which can be expensive while working with high-performance resins and CNT materials such as CNT yarns, bundles, or forests. Fortunately, computational simulations can greatly facilitate CNT composite material design by efficiently predicting the contact angle for a wide range of resins. In this study, a molecular dynamics (MD) framework is developed to determine the contact angle value of high-performance polymer resins on aromatic and aliphatic carbon surfaces (Figure 1). It is determined that monomer length and functional groups have a significant impact on the contact angle. Further, based on these results, qualitative deductions of contact angle values of highperformance resins on CNT materials with amorphous carbon content are made.

Long-Term Fertilization Alters the Chemical Composition of Dissolved Organic Carbon via Regulating Soil Physicochemical Factors

Soil dissolved organic carbon (DOC) plays a key role in fundamental biogeochemical processes; however, the influences of different types of fertilization on the chemical composition and properties of DOC molecules in soils are poorly understood. In this study, DOC samples were extracted from gray desert soils treated with five fertilization treatments 1) chemical nitrogen, phosphorus and potassium fertilizers; 2) pig and cattle manure; 3) 50% nitrogen from manure and 50% nitrogen from chemical fertilizer; 4) total chemical fertilizers and total manure; and 5) no fertilization (control). Data were compared by a combination of Fourier-transform infrared spectroscopy, 13C nuclear magnetic resonance, and statistical analyses. Results showed that manure application increased the aliphatic carbon and decreased the aromatic carbon levels, implying manure application promotes the transformation of labile carbon to stable carbon structures. Redundancy analysis indicated that available nutrients and available forms of magnesium were positively associated with the labile carbon groups, and the available forms of calcium were positively associated with the stable carbon groups. These results demonstrated that the availability of soil nutrients and minerals are influential factors on DOC turnover. Moreover, our results showed that fertilization method had negative direct effects on DOC transformation and positive indirect effects on DOC turnover via soil physicochemical factors, and various forms of mineral ions were the strongest explanatory factors of DOC variation. These findings indicated that soil physicochemical factors play an important role as mediators in the influence of fertilization practices on the chemical composition of DOC and turnover of carbon-containing functional groups in DOC.

2D/3D Halide Perovskites for Optoelectronic Devices

The traditional three-dimensional (3D) halide perovskites (HPs) have experienced rapid development due to their highly power conversion efficiency (PCE). However, the instability of 3D perovskite on humidity and UV irradiation blocks their commercialization. In the past few years, two-dimensional (2D) halide perovskites attract much attention because they behave better stability due to the water resistance of the aliphatic carbon chains in the 2D perovskite lattice. In this review, we categorize the 2D/3D perovskites based on the applications [i.e., solar cells (SCs), light-emitting diodes (LEDs) and photodetectors (PDs)]. We further discuss the recent efforts in the performance enhancement of the 2D/3D perovskite-based devices. However, there are still some difficulties before 2D/3D HPs is fully commercialized. We will provide some scientific and technical challenges and prospects in the article to point out the future direction.

Laboratory Investigations Coupled to VIR/Dawn Observations to Quantify the Large Concentrations of Organic Matter on Ceres

Organic matter directly observed at the surface of an inner planetary body is quite infrequent due to the usual low abundance of such matter and the limitation of the infrared technique. Fortuitously, the Dawn mission has revealed, thanks to the Visible and InfraRed mapping spectrometer (VIR), large areas rich in organic matter at the surface of Ceres, near Ernutet crater. The origin of the organic matter and its abundance in association with minerals, as indicated by the low altitude VIR data, remains unclear, but multiple lines of evidence support an endogenous origin. Here, we report an experimental investigation to determine the abundance of the aliphatic carbon signature observed on Ceres. We produced relevant analogues containing ammoniated-phyllosilicates, carbonates, aliphatic carbons (coals), and magnetite or amorphous carbon as darkening agents, and measured their reflectance by infrared spectroscopy. Measurements of these organic-rich analogues were directly compared to the VIR spectra taken from different locations around Ernutet crater. We found that the absolute reflectance of our analogues is at least two orders of magnitude higher than Ceres, but the depths of absorption bands match nicely the ones of the organic-rich Ceres spectra. The choices of the different components are discussed in comparison with VIR data. Relative abundances of the components are extrapolated from the spectra and mixture composition, considering that the differences in reflectance level is mainly due to optical effects. Absorption bands of Ceres’ organic-rich spectra are best reproduced by around 20 wt.% of carbon (a third being aliphatic carbons), in association with around 20 wt.% of carbonates, 15 wt.% of ammoniated-phyllosilicate, 20 wt.% of Mg-phyllosilicates, and 25 wt.% of darkening agent. Results also highlight the pertinence to use laboratory analogues in addition to models for planetary surface characterization. Such large quantities of organic materials near Ernutet crater, in addition to the amorphous carbon suspected on a global scale, requires a concentration mechanism whose nature is still unknown but that could potentially be relevant to other large volatile-rich bodies.

Wetting Simulations of High-Performance Polymer Resins on Carbon Surfaces as a Function of Temperature Using Molecular Dynamics

Resin/reinforcement wetting is a key parameter in the manufacturing of carbon nanotube (CNT)-based composite materials. Determining the contact angle between combinations of liquid resin and reinforcement surfaces is a common method for quantifying wettability. As experimental measurement of contact angle can be difficult when screening multiple high-performance resins with CNT materials such as CNT bundles or yarns, computational approaches are necessary to facilitate CNT composite material design. A molecular dynamics simulation method is developed to predict the contact angle of high-performance polymer resins on CNT surfaces dominated by aromatic carbon, aliphatic carbon, or a mixture thereof (amorphous carbon). Several resin systems are simulated and compared. The results indicate that the monomer chain length, chemical groups on the monomer, and simulation temperature have a significant impact on the predicted contact angle values on the CNT surface. Difunctional epoxy and cyanate ester resins show the overall highest levels of wettability, regardless of the aromatic/aliphatic nature of the CNT material surface. Tetrafunctional epoxy demonstrates excellent wettability on aliphatic-dominated surfaces at elevated temperatures. Bismaleimide and benzoxazine resins show intermediate levels of wetting, while typical molecular weights of polyether ether ketone demonstrate poor wetting on the CNT surfaces.

Synthesis and Enantioselective Pharmacokinetic/Pharmacodynamic Analysis of New CNS-Active Sulfamoylphenyl Carbamate Derivatives

We recently reported a new class of carbamate derivatives as anticonvulsants. Among these, 3-methylpentyl(4-sulfamoylphenyl)carbamate (MSPC) stood out as the most potent compound with ED50 values of 13 mg/kg (i.p.) and 28 mg/kg (p.o.) in the rat maximal electroshock test (MES). 3-Methylpropyl(4-sulfamoylphenyl)carbamate (MBPC), reported and characterized here, is an MSPC analogous compound with two less aliphatic carbon atoms in its structure. As both MSPC and MBPC are chiral compounds, here, we studied the carbonic anhydrase inhibitory and anticonvulsant action of both MBPC enantiomers in comparison to those of MSPC as well as their pharmacokinetic properties. Racemic-MBPC and its enantiomers showed anticonvulsant activity in the rat maximal electroshock (MES) test with ED50 values in the range of 19–39 mg/kg. (R)-MBPC had a 65% higher clearance than its enantiomer and, consequently, a lower plasma exposure (AUC) than (S)-MSBC and racemic-MSBC. Nevertheless, (S)-MBPC had a slightly better brain permeability than (R)-MBPC with a brain-to-plasma (AUC) ratio of 1.32 (S-enantiomer), 1.49 (racemate), and 1.27 (R-enantiomer). This may contribute to its better anticonvulsant-ED50 value. The clearance of MBPC enantiomers was more enantioselective than the brain permeability and MES-ED50 values, suggesting that their anticonvulsant activity might be due to multiple mechanisms of action.

Surface Chemical Heterogeneity of Low Rank Coal Characterized by Micro-FTIR and Its Correlation with Hydrophobicity

Micro-Fourier transform infrared (micro-FTIR) spectroscopy was used to correlate the surface chemistry of low rank coal with hydrophobicity. Six square areas without mineral impurities on low rank coal surfaces were selected as testing areas. A specially-designed methodology was applied to conduct micro-FTIR measurements and contact angle tests on the same testing area. A series of semi-quantitative functional group ratios derived from micro-FTIR spectra were correlated with contact angles, and the determination coefficients of linear regression were calculated and compared in order to identify the structure of the functional group ratios. Finally, two semi-quantitative ratios composed of aliphatic carbon hydrogen, aromatic carbon hydrogen and two different types of carbonyl groups were proposed as indicators of low rank coal hydrophobicity. This work provided a rapid way to predict low rank coal hydrophobicity through its functional group composition and helped us understand the hydrophobicity heterogeneity of low rank coal from the perspective of its surface chemistry.

Generality of Correlation between Yield and Reduced Mass of Raw Materials in Organic Reactions

To validate a generality of the correlation between product yield and reduced mass of raw materials, the regression analysis of 129 reaction examples (55 as a sample size) including at least 66 types of reactions used in syntheses of natural products such as peptides and terpenes was conducted. It was possible to predict a yield of a variety of synthetic reactions for a synthesis of natural product with many aliphatic carbon chains by applying a reduced mass, adjusted with a molecular weight and the number of rotatable bond, to the regression equation. Moreover, it was found that the increase in yield due to a use of the adjusted reduced mass correlated with the harmonic mean of the molar heat capacity of raw materials and was expressed as a second-order approximation within the analysis range.<br>

Generality of Correlation between Yield and Reduced Mass of Raw Materials in Organic Reactions

To validate a generality of the correlation between product yield and reduced mass of raw materials, the regression analysis of 129 reaction examples (55 as a sample size) including at least 66 types of reactions used in syntheses of natural products such as peptides and terpenes was conducted. It was possible to predict a yield of a variety of synthetic reactions for a synthesis of natural product with many aliphatic carbon chains by applying a reduced mass, adjusted with a molecular weight and the number of rotatable bond, to the regression equation. Moreover, it was found that the increase in yield due to a use of the adjusted reduced mass correlated with the harmonic mean of the molar heat capacity of raw materials and was expressed as a second-order approximation within the analysis range.<br>

Characterization of Nanostructure Evolution in Coal Molecules of Different Ranks

Four coals samples at different ranks were analyzed by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and solid-state 13C nuclear magnetic resonance (NMR). The calculated coal molecular model was constructed according to the experimental data. The mode of evolution of four coal molecules with different metamorphic degrees was explored. The results indicate that the nanostructures of these four coal molecules mainly consist of aromatic structures, aliphatic structures and oxygen-containing functional groups. The coal metamorphic degree is the most important factor affecting the evolution of the coal molecular nanostructure. By increasing the coal rank, the aromatic carbon content and aromatic system increase, while the aliphatic carbon content and aliphatic system decrease, and the species and content of oxygen containing functional groups are also reduced. During the evolution of the molecular microcrystalline structure, the degree of vertical order of the aromatic structural unit, the flatness of the aromatic structural unit (La), the average crystallite stacking height (Lc), and the average number of crystallites in a stack (n) increase, while the interlayer distance between aromatic sheets (d002) decreases; the short-range ordering of the coal structure is mainly caused by changes in the orientational arrangement from intramolecular aromatic layers to intermolecular aromatic layers when low-rank coal molecules evolve to high rank coal molecules. The structural evolution mechanism of coal molecules of different ranks has been revealed through the analysis of the mode of evolution of the molecular structure the coal. This study enables us to better understand the nanostructure evolution mechanism of coal molecules at different ranks.