Chirality Discrimination at Binary Organic|Water Interfaces Monitored by Interfacial Tension Measurements with Preliminary Comparison with Molecular Dynamics Simulations.

Chirality discrimination at a binary toluene (organic)/water(aqueous) interface between R- or S-Tol-BINAP (2,2'-Bis(di-p-tolylphosphino)-1,1'-binaphthyl) molecules and the water-soluble serine chiral specie is examined for the first time, using a combination of interfacial tension measurements and molecular dynamic simulations. Experimental interfacial measurements exhibit a clear chirality-controlled difference when a homochiral versus a heterochiral enantiomeric pairs are introduced at the interfaces. The related molecular dynamics simulations support the experimental results and provide further molecular insight of intermolecular interactions at the interfaces. The results indicate that interfacial tension measurements can capture the preferential interactions which exist between different pairs of enantiomers at the binary interfaces, opening up a new way for probing chirality discrimination at liquid-liquid interfaces.

Solvating power regulation enabled low concentration electrolyte for lithium batteries.

Li+ solvation structures have a decisive influence on the electrode/electrolyte interfacial properties and battery performances. Reduced salt concentration may result in an organic rich solid electrolyte interface (SEI) and catastrophic cycle stability, which makes low concentration electrolytes (LCEs) rather challenging. Solvents with low solvating power bring in new chances to LCEs due to the weak salt-solvent interactions. Herein, an LCE with only 0.25 mol L-1 salt is prepared with fluoroethylene carbonate (FEC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (D2). Molecular dynamics simulations and experiments prove that the low solvating power solvent FEC not only renders reduced desolvation energy to Li+ and improves the battery kinetics, but also promotes the formation of a LiF-rich SEI that hinders the electrolyte consumption. Li||Cu cell using the LCE shows a high coulombic efficiency of 99.20%, and LiNi0.6Co0.2Mn0.2O2||Li cell also exhibits satisfying capacity retention of 89.93% in 200 cycles, which demonstrates the great potential of solvating power regulation in LCEs development.

Stacking nuances modulate the mechanical properties of graphene/SnO2nanocomposites.

Due to its superior mechanical properties, graphene is widely used as reinforcement materials in nanocomposites. In this work, a series of indentation simulations was performed, using finite element method, to investigate the mechanical properties of graphene/TiO2and graphene/SnO2nanocomposite films. The force-displacement curves obtained from simulations were first compared to analytical results, which demonstrates that with increasing the thicknesses of metal oxide layers, the mechanical responses of nanocomposites exhibit a transition from non-linear behaviors to linear behaviors. Furthermore, consistent with literature works, increasing graphene volume fraction can enhance the Young's modulus of the corresponding heterostructure. Interestingly, this enhancement can be modulated by nuances in stacking orders, i.e. layer arrangements, of nanocomposites. Through analyzing stress and strain distributions, the underlying mechanisms were proposed. Our results reported here provide comprehensive characterizations and understandings on the reinforcement effects of graphene on graphene/metal oxide nanocomposites.

Experimental studies on the effect of ultrasonic treatment and hydrogen donors on residual oil characteristics.

Residual oil, the residue after the distillation of crude oil, imposes deleterious effects on refinery due to its high viscosity and asphaltene content. In this context, ultrasonic technology has been widely applied in refining processes given its high efficiency and minimal environmental impacts. To guide the selection of operation parameters, in this work, we probed the effect of treatment duration, power, and hydrogen donor on the characteristics of residual oil under ultrasonic treatments. Underlying mechanisms of ultrasonic treatments, in the absence and presence of hydrogen donors, were verified through systematically analyzing viscosity, component conversion, molecular weight, hydrogen distribution, and functional groups of residual oil. While viscosity reductions under low-power density treatment are caused by colloidal system disaggregation, high-power density treatment can bring in both chemical bond cleavage and colloidal system disaggregation. In addition, adding hydrogen donor can effectively prevent radical recombination, and thus increases the yield of saturate. These results provide fundamental understandings on the effects of ultrasonic treatments.

Laser-Induced Tar-Mediated Sintering of Metals and Refractory Carbides in Air.

Refractory metals and their carbides possess extraordinary chemical and temperature resilience and exceptional mechanical strength. Yet, they are notoriously difficult to employ in additive manufacturing, due to the high temperatures needed for processing. State of the art approaches to manufacture these materials generally require either a high-energy laser or electron beam as well as ventilation to protect the metal powder from combustion. Here, we present a versatile manufacturing process that utilizes tar as both a light absorber and antioxidant binder to sinter thin films of aluminum, copper, nickel, molybdenum, and tungsten powder using a low power (<2W) CO2 laser in air. Films of sintered Al/Cu/Ni metals have sheet resistances of ∼10-1 ohm/sq, while laser-sintered Mo/W-tar thin films form carbide phases. Several devices are demonstrated, including laser-sintered porous copper with a stable response to large strain (3.0) after 150 cycles, and a laserprocessed Mo/MoC(1-x) filament that reaches T ∼1000 °C in open air at 12 V. These results show that tar-mediated laser sintering represents a possible low energy, cost-effective route for engineering refractory materials and one that can easily be extended to additive manufacturing processes.

Laser-sculptured ultrathin transition metal carbide layers for energy storage and energy harvesting applications.

Ultrathin transition metal carbides with high capacity, high surface area, and high conductivity are a promising family of materials for applications from energy storage to catalysis. However, large-scale, cost-effective, and precursor-free methods to prepare ultrathin carbides are lacking. Here, we demonstrate a direct pattern method to manufacture ultrathin carbides (MoCx, WCx, and CoCx) on versatile substrates using a CO2 laser. The laser-sculptured polycrystalline carbides (macroporous, ~10-20 nm wall thickness, ~10 nm crystallinity) show high energy storage capability, hierarchical porous structure, and higher thermal resilience than MXenes and other laser-ablated carbon materials. A flexible supercapacitor made of MoCx demonstrates a wide temperature range (-50 to 300 °C). Furthermore, the sculptured microstructures endow the carbide network with enhanced visible light absorption, providing high solar energy harvesting efficiency (~72 %) for steam generation. The laser-based, scalable, resilient, and low-cost manufacturing process presents an approach for construction of carbides and their subsequent applications.

Competitive Adsorption of Naphthenic Acids and Polyaromatic Molecules at a Toluene-Water Interface.

The early-stage competitive co-adsorption of interfacially active naphthenic acids (NAs) and polyaromatic (PA) molecules to a toluene-water interface from the bulk toluene phase was studied using molecular dynamics (MD) simulation. The NA molecules studied had the same polar functional group but different cycloaliphatic nonpolar tails, and a perylene bisimide (PBI)-based molecule was used as a representative PA compound. The results from our simulations suggest that the size and structural features of NA molecules greatly influence the interfacial activity of PA molecules and partitioning of NA molecules at the toluene-water interface. At low concentrations of PA (∼2.3 wt %) and NA (∼0.4 wt %) molecules, NA molecules containing large cycloaliphatic rings (e.g., four rings) or with a very long aliphatic tail (e.g., carbon chain length of 14) were observed to impede the migration of PA molecules to the interface, whereas small NA molecules containing two cycloaliphatic rings had little effect on the adsorption of PA molecules at the toluene-water interface. At high NA concentrations, the adsorption of PA molecules (∼5.75-17.25 wt %) was greatly hindered by the presence of small NA molecules (∼1.6-4.8 wt %) due to the solvation of PA nanoaggregates in the bulk. Adsorption mechanisms of PA and NA molecules at toluene-water interfaces were clarified through a detailed analysis on the interactions among different species in the system. The results obtained from this work provide insights into designing appropriate chemical demulsifiers or co-demulsifiers for breaking water-in-oil emulsions of great industrial applications.

Reduction of Water/Oil Interfacial Tension by Model Asphaltenes: The Governing Role of Surface Concentration.

In this work, pendant drop techniques and molecular dynamics (MD) simulations were employed to investigate the effect of asphaltene concentrations on the interfacial tension (IFT) of the oil/water interface. Here, oil and asphaltene were represented by, respectively, common organic solvents and Violanthrone-79, and two types of concentration, i.e., bulk concentration and surface concentration, were examined. Correlations between the IFTs from experiments and MD simulations revealed that surface concentration, rather than the commonly used bulk concentration, determines the reduction of oil/water IFTs. Through analyzing the hydrogen bonding, the underlying mechanism for the IFT reduction was proposed. Our discussions here not only enable the direct comparison between experiments and MD simulations on the IFTs but also help with future interfacial studies using combined experimental and simulation approaches. The methodologies used in this work can be extended to many other oil/water interfaces in the presence of interfacially active compounds.

Role of Naphthenic Acids in Controlling Self-Aggregation of a Polyaromatic Compound in Toluene.

In this work, a series of molecular dynamics simulations were performed to investigate the effect of naphthenic acids (NAs) in early stage self-assembly of polyaromatic (PA) molecules in toluene. By exploiting NA molecules of the same polar functional group but different aliphatic/cycloaliphatic nonpolar tails, it was found that irrespective of the presence of the NA molecules in the system, the dominant mode of π-π stacking is a twisted, offset parallel stacking of a slightly larger overlapping area. Unlike large NA molecules, the presence of small NA molecules enhanced the number of π-π stacked PA molecules by suppressing the hydrogen bonding interactions among the PA molecules. Smaller NA molecules were found to have a higher tendency to associate with PA molecules than larger NA molecules. Moreover, the size and distribution of π-π stacking structures were affected to different degrees by changing the size and structural features of the NA molecules in the system. It was further revealed that the association between NA and PA molecules, mainly through hydrogen bonding, creates a favorable local environment for the overlap of PA cores (i.e., π-π stacking growth) by depressing the hydrogen bonding between PA molecules, which results in the removal of some toluene molecules from the vicinity of the PA molecules.

Molecular Dynamics Simulations Reveal Inhomogeneity-Enhanced Stacking of Violanthrone-78-Based Polyaromatic Compounds in n-Heptane-Toluene Mixtures.

We elucidated the effect of inhomogeneity in solutes on the aggregation of our representative polyaromatic (PA) compounds through a series of molecular dynamics simulations. Two kinds of solutes, a single type of PA compounds and a mixture of four types of PA compounds, were simulated in toluene, n-heptane, and heptol (mixture of toluene and n-heptane). The geometries of the resultant aggregates were quantified using gyradius ratios. Our results revealed that in toluene, while a single type of PA compound can only form short-cylinder-like aggregates, by having a solute mixture, parallel stacking of PA cores is enhanced, leading to the formation of one-dimensional (1D) rod-like structure. The enhanced stacking is caused by collective arrangement of the PA molecules; i.e., PA compounds of different types appear in an alternating manner in the aggregate. In addition, while the aggregated geometries of a single type of PA compounds were found to be affected by the composition of the solvents, the existence of the 1D structure formed by mixture seems to be insensitive to the solvents. On the other hand, the longest range of stacking is achieved by having a small amount of toluene ("good" solvent) in n-heptane ("bad" solvent).

A dimension map for molecular aggregates.

A pair of gyradius ratios, defined from the principal radii of gyration, are used to generate a dimension map that describes the geometry of molecular aggregates in water and in organic solvents. Molecular dynamics simulations were performed on the aggregation of representative biomolecules and polyaromatic compounds to demonstrate application of the dimension map. It was shown that molecular aggregate data on the dimension map were bounded by two boundary curves, and that the map could be separated into three regions representing three groups of structures: one-dimensional rod-like structures; two-dimensional planar structures or short-cylinder-like structures; and three-dimensional sphere-like structures. Examining the location of the aggregates on the dimension map and how the location changes with solvent type and solute material parameter provides a simple yet effective way to infer the aggregation manner and to study solubility and mechanism of aggregation.

One-dimensional self-assembly of polyaromatic compounds revealed by molecular dynamics simulations.

A series of molecular dynamics simulations were performed on the self-assembly of polyaromatic (PA) compounds in n-heptane. These compounds possess the same PA core but systematically varied side-chain lengths. Regardless of the side-chain lengths, the simulations revealed the formation of one-dimensional (1D) self-assemblies resulting mainly from parallel stacked PA cores. The length over which the parallel stacking persists was found to be 3-5.6 nm. The 1D self-assembly was not observed for the same PA compounds in water or toluene, suggesting the importance of solvent properties in its formation. In particular, n-heptane can prevent the side chains from interfering with PA core stacking while having limited attraction with the cores, which facilitates the 1D self-assembling. These findings, revealed at the molecular level, provide insights into controlling the self-assembling process in the design of optical and electronic nanodevices.