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The incorporation of cadmium telluride (CdTe) nanowire photovoltaics offers the possibility to overcome energy loss in solar cells associated with minority carrier recombination, and to increase optical efficiency by reducing reflection. In this study, CdTe nanowires (NWs) were synthesized from individual nanoparticles encapsulated with thioglycolic acid (TGA) and 1-thioglycerol (TGC) via self-assembly under illumination by a 550 nm wavelength light. This wavelength resulted in the self-assembly of nanoparticles into nanowires. TGA-stabilized CdTe NWs (TGA-NWs) and TGC-stabilized CdTe NWs (TGC-NWs) that made up the self-assembly were different crystalline structures. Most of the produced nanowires were straight and varied in length from 1.2 to 3.9 µm. The oxidation of Te2− in CdTe nanoparticles under a 550 nm wavelength light resulted in the assembly of nanowires consisting of several layers of individual nanoparticles. Transmission electron microscopy was performed to characterize the synthesized nanostructures. Photoluminescence analysis showed that the wavelength of the nanostructures was slightly blue-shifted.

We present a design of a nanoscale inertial measurement unit or a data archive using a graphene-nanoflake (GNF) sandwiched between crossed graphene-nanoribbon (GNR) junctions. When an external force applied is below the retracting force, the inertial force exerted on the movable GNF can telescope it. Then, the self-restoring force increases as the attractive van der Waals force between the GNF and the GNRs, which enables the GNF to automatically and fully retract back into the sandwich position immediately after the externally applied force is released. When the external force exceeds the retracting force, the GNF escapes from the crossed GNR junctions, which enables the device to be used as non-volatile memory. The heterostructure of GNR/h-BN/GNR can be considered as an advanced structure in the proposed scheme.

Cadmium telluride (CdTe) nanoparticles (NPs) are known for their unique physical and chemical properties. NP synthesis via a size-controlled procedure has become an intriguing research topic because NPs exhibit novel optical and physical properties depending on their size. Their sizes and properties can vary depending on the types and concentrations of stabilizers, which are bound to the surface of the NPs and protect the NPs from aggregation. In this study, we synthesized CdTe NPs stabilized by thioglycolic acid (TGA), 1-thioglycerol (TGC), and L-cysteine (L-C). The ratio of stabilizer to Cd2+ was 1:2.4. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence (PL) were employed for characterization of the NPs. The average sizes of the synthesized NPs were 4.2, 4.1, and 3.7 nm for TGA, TGC, and L-C, respectively. The maximum fluorescent emission peaks of the three NP solutions were at 554.9, 551.6, and 538.3 nm for TGA, TGC, and L-C, respectively. The produced particles were crystalline in structure with a face-centered cubic (fcc) system.

Superlubric motions of graphene nanoflakes (GNFs) on graphene have opened up more applications of graphene for micromachines and nanomachines. Here, we investigate the dynamic behavior of a GNF shuttle on a graphene nanoribbon (GNR) with carbon nanotube (CNT) blocks via molecular dynamics simulations. The GNF moves on a GNR superlubrically, and the CNTs as building blocks induce bistable potential wells so that the GNF is stabilized. MD simulation results indicate that when a GNF shuttle approaches the CNTs, a potential well is created by an increase in the attractive van der Waals energy between the GNF and CNTs, and bistability at the local energy minima positions can be achieved near the CNTs. In order for the GNF shuttle to escape the local energy minima positions, a high external force must be applied to overcome the potential energy barrier. However, after the GNF shuttle escapes from one of the bistable positions, only a low external force is required to stabilize the GNF shuttle. This work explicitly demonstrates that a GNF-GNR/CNT system could be applied to alternative nonvolatile memory and high-speed mass storage by using GNR-CNT arrays.

In our previous studies, it was proven that ionic liquids can be a good synergist with poly(N-vinylcaprolactam) [PVCap, a polymeric kinetic hydrate inhibitor (KHI)] against methane or natural gas hydrate formation. In particular, 1-hexyl-1-methylpyrrolidinium tetrafluoroborate (HMP-BF4) showed the best performance for natural gas hydrate inhibition among the ionic liquids tested. In this study, we report the result of performance tests on kinetic inhibition of natural gas hydrate formation with a mixture of PVCap and HMP-BF4 in the presence of an additional oil phase. At various water cuts (20, 50, and 80%) with 3.5 wt % aqueous NaCl solution and mineral oil, the KHI performance of PVCap alone and a mixture of 0.5 wt % PVCap and 0.5 wt % HMP-BF4 was evaluated. This was performed by measuring the induction time for the synthetic natural gas hydrate formation, in addition to the pressure, temperature, and torque of the system investigated. Calculations were carried out to determine the amount of water conve...

Deep eutectic solvents (DESs) are emerging as innovative materials and regarded as cost effective IL replacements. Mixing of DESs with other solvents modifies their properties for specific applications. One of the popular DESs is made of choline chloride and glycerol named as glyceline. Densities of glyceline mixed with water, methanol, ethanol, or iso-propanol were measured in the temperature range of 283.15 to 343.15 or 323.15 K over the entire range of composition at ambient pressure. The temperature dependency was correlated by a quadratic equation for the respective systems. The excess molar volumes were evaluated and correlated by a Redlich-Kister type equation with temperature-dependent parameters. Furthermore, other derived volumetric properties such as the volume expansivity and the apparent molar volume were calculated using the measured data. The H-bond formation is more likely to occur in alcohol solutions than in aqueous solution as inferred by the comparison of the maximum deviations from ideal mixing and the limiting apparent molar volume of glyeline in the solutions.

The effects of high-intensity interval training (HIIT) interventions on functional brain changes in older adults remain unclear. This preliminary study aimed to explore the effect of physical exercise intervention (PEI), including HIIT, on cognitive function, physical performance, and electroencephalogram patterns in Korean elderly people.We enrolled six non-dementia participants aged65 years from a community health center. PEI was conducted at the community health center for 4 weeks, three times/week, and 50 min/day. PEI, including HIIT, involved aerobic exercise, resistance training (muscle strength), flexibility, and balance. Wilcoxon signed rank test was used for data analysis.After the PEI, there was improvement in the 30-second sit-to-stand test result (16.2±7.0 times vs. 24.8±5.5 times,Our HIIT PEI program effectively improved cognitive function, physical fitness, and electroencephalographic markers in elderly individuals; thus, it could be beneficial for improving functional brain activity in this population.

Tetra-iso-amyl ammonium bromide (TiAAB), one of the quaternary ammonium salts, was investigated as a semiclathrate former for its potential application in natural gas storage. The dissociation equilibrium temperature of pure TiAAB semiclathrate was the highest at a stoichiometric concentration (3.7 mol%) of TiAAB·26.0H2O. The dissociation enthalpy of pure TiAAB (3.7 mol%) semiclathrate was 253.0 ± 0.5 J/g using a differential scanning calorimeter (DSC). The thermodynamic stability of the CH4 + TiAAB semiclathrate was significantly higher than that of the CH4 gas hydrate. The CH4 + TiAAB (3.7 mol%) semiclathrate was thermodynamically stable at temperatures higher than 300 K for the pressure range of 1.5–8.5 MPa. 13C NMR and in situ Raman spectroscopy revealed that CH4 molecules were enclathrated in the small cages of the TiAAB semiclathrate and a CH4 inclusion did not affect the semiclathrate structure. The overall experimental results clearly indicate that the TiAAB semiclathrate can trap CH4 molecules at favorable conditions and thus it has a potential for natural gas storage.

To identify the synergetic inhibition effects of ionic liquids (ILs) containing tetrafluoroborate anion (BF4–), various ILs, poly(N-vinylcaprolactam) (PVCap), commercially available polymeric hydrate inhibitor, and their mixtures, were tested as kinetic hydrate inhibitors (KHIs) for natural gas hydrate formation. The experimental results revealed that PVCap–IL mixtures exhibited significantly higher KHI performance. In particular, the mixture of PVCap and 1-hexyl-1-methylpyrrolidinium tetrafluoroborate (HMP-BF4) showed the best hydrate inhibition effectiveness, even under higher pressures. As HMP-BF4 also exhibited the highest hydrate-nucleation-inhibiting performance when it was used alone, further experiments were performed using the mixtures of PVCap and HMP-BF4 at various combinational concentrations. As a result of the experiments, the combination of 1.0 wt % PVCap and 0.5 wt % HMP-BF4 was found to provide the longest induction time. The excellent synergetic effect of the ILs on natural gas hydrate i...

Various ionic liquids (ILs) were tested as CH 4 hydrate inhibitors with/without polymeric hydrate inhibitor, PVCap. Equilibrium dissociation conditions for CH 4 hydrate were measured by the isochoric method in the presence of 10 wt% of ILs and they moved towards inhibition region as much as 1.4–1.8 K. Induction times of CH 4 hydrate formation were also measured in the presence of the individual ILs at various concentrations, and of the mixtures of PVCap and ILs. Some ILs showed better CH 4 hydrate inhibition behaviour than did PVCap. The mixtures of PVCap and several ILs exhibited enhanced kinetic inhibition effects for CH 4 hydrate formation.

Ionic liquids of 1-hydroxyethyl-1-methylmorpholinium chloride (HEMM-Cl) and 1-hydroxyethyl-1-methylmorpholinium tetrafluoroborate (HEMM-BF4) were synthesized to investigate the different effects of anions in the ionic liquids on the methane hydrate formation kinetics. HEMM-Cl and HEMM-BF4 acted as the kinetic hydrate promoter and inhibitor, respectively. The induction time of HEMM-BF4 solutions increased in proportion to the HEMM-BF4 concentration, and both ionic liquids showed thermodynamic hydrate inhibition effect on methane hydrate formation. The X-ray diffraction pattern of hydrates formed in the presence of both ionic liquids showed that there was no influence on, and no incorporation of ionic liquids into, the crystal structure. Using the dynamic light scattering (DLS) technique, HEMM-Cl was revealed not to form micelles, which implies that HEMM-Cl is nonamphiphilic and its hydrate promotion mechanism is different from that of amphiphilic surfactant promoters. HEMM-Cl might distort the rigid hydrat...

The equilibrium boundaries of CH 4 and CO 2 hydrates were examined in the presence of di-carboxylic acids, glutaric acid and malonic acid, at a mass fraction of 0.1 and 0.01. Including di-carboxylic acids in the water phase shifted the phase boundaries to higher pressure and lower temperature conditions. We attributed this to the formation of hydrogen bonding between the inhibitors and water molecules rather than to the formation of water structures serving as hydrate precursors. In addition, the inhibition effect of shorter carbon-chained malonic acid was better than that of longer-chained glutaric acid due to its higher mole fraction in water phase. This inhibition effect was compared with that of conventional thermodynamic hydrate inhibitors (THIs) used in commercial processes. The comparison showed that the effect of malonic acid was close to that of tri-ethylene glycol for inhibiting the CH 4 hydrate.

The phase equilibrium conditions of CO2 hydrates were examined in the presence of morpholinium and piperidinium ionic liquids (ILs) with a mass fraction of 0.1. The equilibrium conditions were in the ranges of (274.6–281.2) K and (1.80–3.95) MPa. The addition of ILs shifted the hydrate equilibrium conditions to a higher pressure and lower temperature region compared to the hydrate formed from pure water. Piperidinium and morpholinium ILs showed similar inhibition effects in the higher temperature range ≥278.5 K, whereas at lower temperature piperidinium ILs had a slightly better inhibition effect than morpholinium ILs. The anionic species also affected the hydrate inhibition effectiveness. Smaller anions, i.e., Br−, had a slightly better inhibition effect than the bigger ions of BF 4 − .

In this study, the thermodynamic inhibition effects of choline chloride (ChCl, a hydrogen bond acceptor), urea (a hydrogen bond donor), and their mixture (deep eutectic solvent, DES) on CH4 hydrates were investigated with both experimental and computational approaches. The synthesis of DES from the mixture of ChCl and urea was confirmed by measuring its melting temperature through a high-pressure micro-differential scanning calorimeter. Sigma (σ)-profiles of ChCl, urea, and DES obtained by the COSMO-RS software indicated that these substances have great potential to be used as thermodynamic hydrate inhibitors (THIs). The three-phase (gas hydrate (H) – liquid water (Lw) – vapor (V)) equilibria of CH4 hydrates in the presence of ChCl (1.0, 3.0, and 5.0 mol%), urea (1.0, 3.0, and 5.0 mol%), and DES (3.0 mol%) demonstrated that ChCl, urea, and DES contributed to the significant shift of hydrate equilibrium temperature to inhibition regions at a specified pressure and thus can function as effective THIs. Moreover, quantum theory of atoms in molecules (QTAIM) analysis also demonstrated that the strength of hydrogen bonding between inhibitor molecules and hydrate cages (small 512 and large 51262 cages) of CH4 hydrates was in the order of ChCl > DES > urea, which was consistent with experimental results. The experimental and computational results from this study would be helpful for a better understanding of the inhibition mechanism of ChCl, urea, and DES and for their possible application to flow assurance in oil and gas pipelines.

Separation of 1,3-propanediol (1,3-PDO) from fermentation broths becomes a bottleneck in biological production due to its high hydrophilicity and low concentration. Aqueous biphasic systems (ABS) composed of piperidinium-based ionic liquids (ILs) and K2HPO4 could be an alternative to extract 1,3-propanediol from fermentation broths. In this study, the ability of piperidinium-based ILs to form ABS with aqueous K2HPO4 solution was investigated. Binodal curves and tie-lines and tie-line length were evaluated by three parameter equation and mass balances for each components in top and bottom phases. The piperidinium-based ILs was effective on promoting ABS formation in the presence of K2HPO4 and the forming ability of ABS increased with alkyl chain length of cations in ILs. The volume ratio to top and bottom phase decreased with K2HPO4 concentration and alkyl chain length of cations in ILs. However, above 20 wt % of K2HPO4, the partitioning of water into top phase is dominant, resulting in low phase volume ra...

With the goal of discovering a more effective type of thermodynamic hydrate inhibitors (THIs), the phase equilibrium conditions of CH4 hydrates were examined in the presence of morpholinium and piperidinium ionic liquids (ILs) at a mass fraction of 0.1. It was observed that the addition of ILs shifted the hydrate equilibrium conditions toward higher pressure and lower temperature compared with those of hydrates formed from pure water. Both cationic and anionic species influenced the equilibrium conditions of the CH4 hydrate. The piperidinium ILs showed better inhibition effect than did the morpholinium ILs at the same species of counteranions. The result may be due to the more hydrophobic nature of piperidinium ILs, which have a higher affinity for CH4 molecules. It was also seen that the inhibition effect of BF4– ions was stronger than that of Br– ions for both piperidinium and morpholinium ILs. Thus, the inhibition effect became stronger in the order: N-ethyl-N-methylpiperidinium tetrafluoroborate ([EMP...

Partially side-opened carbon nanopeapods show great potential for various applications. Here, we investigated the schematics and energetics of a nonvolatile nanomemory element, based on a C60 fullerene encapsulated in a partially opened carbon nanopeapod, using empirical interatomic interaction potential functions. Bistability of the van der Waals potential energy is achieved from the positional change of the encapsulated C60 fullerene, and the encapsulated C60 fullerene can shuttle between bistable positions, under alternatively applied force fields. Since the C60 fullerene can retain its position without recharging, the proposed system can operate as a nonvolatile memory device. These results can be useful for the understanding of new molecular machines.

Thiol-capped cadmium telluride (CdTe) nanoparticles (NPs) self-assembled into nanowires (NWs) under dark conditions, and the evolutionary process was investigated. Thiolglycolic acid (TGA) was selected as one of the stabilizers and a TGA-to-Cd ion ratio of 1.3 rather than the traditional 2.4 ratio was used. The reduced amount of the stabilizer and the oxidation of tellurium ions on CdTe NP surface under dark conditions resulted in reorganization from individual NPs into NWs consisting of multi-layers of individual NPs. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to characterize the synthesized nanostructures. The NWs produced were straight and long, with lengths ranging from 500 nm to 10 μm. Photoluminescence (PL) showed that the nanostructure wavelengths were slightly blue-shifted from 546 to 539 nm. Both control of the amount of stabilizer and oxidation of Te ions acted as driving forces to form NWs. Thus, small modifications in synthesis yielded a major difference in the final nanomaterial structure. The suggested synthetic procedure provides a viable pathway for the fabrication of nanomaterials.

We have investigated the motion of a C60 molecule absorbed on sinusoidal graphene nanoflake (GNF) via molecular dynamics simulations. Since C60 deposited on sinusoidal GNF is favorable on energetic grounds, the C60 molecule moved toward one of the valleys of sinusoidal GNF without energy barrier. So no sooner the C60 molecule was deposited on the sinusoidal GNF, then the C60 molecule immediately began to move toward the valley of the sinusoidal GNF Since the position of the C60 molecule can be changed by externally applied force fields and has a binding energy of 0.754 eV in the valley of sinusoidal GNF, the sinusoidal C60/GNF can be applied to a switchable nonvolatile memory device. This work provides the probability of alternative 'bucky shuttle' memory based on the sinusoidal C60/GNF hybrid nanostructure.

This study examined the thermodynamic stability and guest gas inclusion of tetra-iso-amyl ammonium bromide (TiAAB) semiclathrates with CO2, N2, or CO2 (20%) + N2 (80%), with a primary focus on semiclathrate phase equilibria and Raman spectra. The three-phase (H-LW-V) equilibria of TiAAB semiclathrates with CO2, N2, or CO2 (20%) + N2 (80%) were measured at a stoichiometric concentration (TiAAB 3.7 mol%) using both a conventional isochoric method and a stepwise differential scanning calorimeter (DSC) method. The phase equilibria demonstrated that TiAAB (3.7 mol%) semiclathrates with CO2, N2, or CO2 (20%) + N2 (80%) were significantly stabilized compared with the corresponding CO2, N2, or CO2 (20%) + N2 (80%) gas hydrates. The enclathration of CO2 and N2 molecules in the cages of TiAAB semiclathrates was clearly confirmed via Raman spectroscopy. The experimental results indicate that TiAAB semiclathrates can incorporate CO2 and N2 into the cage lattices at elevated temperatures and lowered pressures and are potential materials for CO2 capture.

Succinic acid is an important precursor in industries producing biopolymers, pharmaceutical and food additives and green solvents. However, due to the high price of petroleum and the global CO2 emission, the biological production of succinic acid from renewable biomass is a novel process due to the fixation of CO2 into succinate during fermentation. In this study, aqueous two phase systems based on imidazolium ionic liquids/K2HPO4 were used as an effective separation and concentration process for succinic acid. Experimental results show that aqueous two phase systems can be formed by adding appropriate amount of imidazolium ionic liquids to aqueous K2HPO4 solutions in the presence of succinic acid. It can be found that the ability of imidazolium ionic liquids for phase separation followed the order (HMIm)(Br)≒(OMIm)(Br)>(BMIm)(Br)>(EMIm)(Br). The maximum value of extraction efficiency for succinic acid was about 90% and the amount of coextracted water into top phase is proportional to the chain length of cation in imidazolium ionic liquids. It was concluded that the aqueous two phase systems composed of imidazolium ionic liquids/K2HPO4 was effective for the selective extraction and concentration of succinic acid.

Cadmium telluride (CdTe) nanowires were successfully synthesized from individual nanoparticles via self-assembly, and the evolutionary process was investigated. The oxidation of tellurium ions in CdTe nanoparticles under dark conditions led to the assembly of straight nanowires made of several layers of individual nanoparticles. Transmission electron microscopy and scanning electron microscopy were performed to characterize the synthesized nanostructures. The length of the NWs assembled from CdTe NPs ranged from 0.5 to 30 μm. Unlike generally prepared NWs, these NWs were made from individual NPs layered on top of each other. Remarkably, the assembly of individual NPs formed bundles during the intermediate steps before they unraveled into individual NWs. Both control of the amount of stabilizer and oxidation of Te ions acted as driving forces to form NWs. Thus, small modifications in synthesis yielded a major difference in the final nanomaterial structure. The suggested synthetic procedure provides a viable pathway for the fabrication of nanomaterials.

Ionic liquids (ILs) have been proposed as potential inhibitors for preventing gas hydrate formation because their ion pairs effectively interrupt the hydrogen bonding between water molecules. ILs also have broad inhibitory capabilities depending on the specific cation and anion combinations. The final structural design of ILs for hydrate inhibition must be performed after an inhibition mechanism is suggested. In this study, the inhibitory thermodynamic effects of ILs were measured by the hydrate–aqueous liquid–liquid carbon dioxide (CO2) equilibrium, and the experimental results were analyzed based on the hydration free energy of ILs calculated through molecular dynamics study. 1-Hydroxyethyl-1-methylpyrrolidinum chloride showed the best inhibitory performance of the suggested candidates. The anions mostly contributed to the thermodynamic inhibition, but the cations had a marginal impact on CO2 hydrate inhibition. Through fundamental understanding of the inhibition mechanism by both experimental and computational approaches, it is highly possible to provide crucial information for effective ILs to be designed as the CO2 hydrate inhibitor.

As an effective method for extraction of acrylic acid, aqueous two-phase systems based on morpholinium ionic liquids were used in this study. Effects of the alkyl chain length of cation in morpholinium ionic liquids on phase diagram and extraction efficiencies were investigated. Experimental results show that aqueous two phase systems can be formed by adding appropriate amount of morpholinium ionic liquids to aqueous K2HPO4 solutions. It can be found that the ability of morpholinium ionic liquids for phase separation followed the order (HMMor)(Br)>(OMMor)(Br)>(BMMor)(Br)> (EMMor)(Br). There was little difference between binodal curves of imidazolium ionic liquids and those of morpholin- ium ionic liquids. 50~90% of the extraction efficiency was observed for acrylic acid by aqueous two phase extraction of acrylic acid with morpholinium ionic liquids. It can be concluded that morpholinium ionic liquids/K2HPO4 were effec- tive for aqueous two phases extraction of acrylic acid comparing to imidazolium ionic liquids/K2HPO4 systems because of their lower cost.

Pyroprocess for treating spent nuclear fuels has been developed based on electrochemical principles. Process simulation is one of the important methods for process development and experimental data analysis and it is also a necessary approach for pyroprocessing. To date, process simulation of pyroprocessing has been focused on electrorefining and there have been not so many investigations on electrolytic reduction. Electrolytic reduction, unlike electrorefining, includes specific features of gas evolution and porous electrode and, thus, different equations should be considered for developing a model for the process. This study summarized required concepts and equations for electrolytic reduction model development from thermodynamic, mass transport, and reaction kinetics theories which are necessitated for analyzing an electrochemical cell. An electrolytic reduction cell was divided and equations for each section were listed and, then, boundary conditions for connecting the sections were indicated. It is expected that those equations would be used as a basis to develop a simulation model for the future and applied to determine parameters associated with experimental data.

This study examines the thermodynamic, structural, and kinetic characterizations of cyclopentane (CP) + CO2 hydrates in the presence of NaCl for their potential applications in desalination and CO2 capture. Powder X-ray diffraction (PXRD) demonstrated that CP molecules fully occupied the large (51264) cages of CP + CO2 hydrate (structure II), whereas approximately 62% of the small (5 1 2) cages were captured by CO2 molecules. To determine accurate hydration numbers and dissociation enthalpies of CP and CP + CO2 hydrates, cage occupancy of guest molecules revealed by Rietveld refinement of PXRD patterns was combined with integrated areas of endothermic heat-flow curves obtained by a high-pressure micro-differential scanning calorimeter (HP μ-DSC). The addition of CP contributed to a significant stabilization of CO2 hydrate due to CP molecules’ occupation of the large (51264) cages and a subsequent structural transformation to sII. The shift in the equilibrium curves of CO2 + CP + NaCl hydrates to lower-temperature and higher-pressure regions was more significant at higher NaCl concentrations. The cage-filling behavior of guest molecules and the growth patterns revealed by collected time-dependent Raman spectra indicated that the presence of NaCl retarded the growth rate of CO2 + CP hydrate. The experimental results covering hydrate phase equilibria, dissociation enthalpies, hydration numbers, guest distributions, and enclathration behaviors of CO2 + CP hydrates form fundamental reference data for understanding cage-specific guest occupation and growth behaviors of gas hydrates in the presence of salts. The results will also be useful when designing hydrate-based desalination and CO2 capture technologies using CP.

본 연구에서는 가스 하이드레이트 생성 시 첨가된 이온성 액체가 미치는 생성속도의 향상효과를 조사하였다. 이온성 액체로는 Hydroxyethyl-methyl-morpholinium chloride (HEMM-Cl)을 사용하였다. 메탄 하이드레이트의 상평형 곡선을 구하고 생성유도시간과 메탄가스의 소모량을 측정하였다. 20~20,000 ppm의 HEMM-Cl을 준비하여 하이드레이트가 생성될 수 있는 70 bar, 274.15 K 조건에서 실험을 수행하였다. 하이드레이트 생성 속에 대한 비교를 위해 순수한 물과 대표적인 촉진제인 sodium dodecyl sulfate를 같은 조건에서 실험하였다. 실험 결과, 이온성 액체인 HEMM-Cl은 상평형 곡선을 더 높은 압력과 낮은 온도 쪽으로 이동시켰다. 이온성 액체의 첨가 시에는 메탄 하이드레이트의 생성유도시간이 거의 나타나지 않는 것을 알 수 있었다. 메탄가스의 소모량은 모든 농도에서 향상되었고 1,000 ppm에서 가장 많은 양의 가스를 흡수하는 것으로 나타났다. 이온성 액체는 가스 하이드레이트 생성 촉진을 유도하는 것으로 나타났으며 가스저장, 수송 등의 응용기술 개발에 적용이 기대된다. 【In this study, we investigated the kinetics of gas hydrate formation in the presence of ionic liquid (IL). Hydroxyethyl-methyl-morpholinium chloride (HEMM-Cl) was chosen as a material for the promotion effect test. Phase equilibrium curve for $CH_4$ hydrate with aqueous IL solution was obtained and its induction time and consumed amount of $CH_4$ gas were also measured. Aqueous solutions containing 20~20,000 ppm of HEMM-Cl was prepared and studied at 70 bar and 274.15 K. To compare the measured results to those of the conventional promoter, sodium dodecyl sulfate was also tested at the same condition. Result showed that the hydrate equilibrium curve was shifted toward higher pressure and lower temperature region. In addition, the induction time on $CH_4$ hydrate formation in the presence of IL was not shown. The amount of consumed $CH_4$ was increased with the whole range of tested concentration of IL and the highest consumption of $CH_4$ happened at 1,000 ppm of HEMM-Cl. HEMM-Cl induced and enhanced the $CH_4$ hydrate formation with a small amount of addition. Obtained result is expected to be applied for the development of technologies such as gas storage and transport using gas hydrates.】

A tunable graphene-resonator was investigated using classical molecular dynamics modeling and simulations. The fundamental resonance frequency variation of the graphene resonator was found to be very closely related to the average tension acting on both its edges. The initial stain-induced tension could be adjusted by using the mismatch between the negative thermal expansion coefficient of the graphene and the positive thermal expansion coefficient of the substrate, and the deflection-induced tension could be controlled by an electrostatic capacitive force due to the gate voltage. For very small initial axial-strains, the tunable range reached above several hundred gigahertz. As the initial axial-strain on the graphene-resonator increased, both the tunability and the tunable range decreased. The fundamental resonance frequency as a function of the calculated gate voltage was in good agreement with previous experiments. Considering the variables that affect the tension variation, this graphene-resonator is suitable for use as an ultra-sensitive accelerometer, thermo-sensor or weight scale, as well as many other types of sensor.

We presented simple schematics of a nanoscale inertial measurement unit based on the self-retraction motion of the graphene flakes. When an external force is applied to the nanoscale graphite flake, the inertial force exerted on the movable layer can telescope it, then the self-restoring force also arises as the van der Waals force between the interlayers of the flake, which each suspended flake can automatically and fully retract back onto the top of the graphite platform immediately after the externally applied force is released. Since the van der Waals force linearly increases with the increasing size of the flake, the sensing limitation can be controlled. When the external force does not exceed the retracting force, this addressed nanoscale inertial measurement unit can be semi-permanently used. Therefore, the size and the thickness of the graphene flake should be carefully selected with a tradeoff. These graphite flakes can be utilized as a basic structure in various nanoelectromechanical devices, such as switch and memory, linear and angular accelerometers, and pressure sensors.

A tunable graphene-nanoribbon (GNR)-resonator was investigated via classical molecular dynamics simulations. Resonance frequencies increased with increasing externally applied gate-force and axial-strain, and could be tuned above several hundred GHz. Tunable resonance frequencies achieved from the gate force were higher than those achieved from the axial-strain. The operating frequencies of GNR-resonators without axial-strain or with small axial-strains were most widely tuned by the gate, and almost linearly increased with increasing mean deflection. As the axial strain increased, the tunable ranges of the GNR-resonators were exponentially decreased, although the operating frequencies increased. GNR-resonators without axial-strain could be applied to wide-range-tuners, whereas GNR-resonators with high axial-strain could be applied to high-frequency-fine-tuners.

Molecular dynamics methods are used to model the vibrational behavior of a suspended graphene-resonator that absorbs a finite mass at constant temperature. The effective molecular dynamics simulations easily estimate the fundamental frequency shifts of the suspended graphene with attached mass. The resonance frequency of the graphene-resonator can be functionalized by both the attached mass and the applied force. The results obtained from the molecular dynamics simulations were in good agreement with those of previous related experimental and theoretical works. For this graphene-based scaled nanobalance, the possible frequency-shift ranges increased with increasing applied force and with decreasing attached mass, they then reached 75–80% of the fundamental resonance frequency of a bare graphene-resonator. The mass sensitivity of the graphene-resonator reached ∼10 −24 g and a logarithmically linear relationship was found in the frequency-vs-mass curves for attached masses of 10 −21 –10 −19 g.

We propose schematics for an ultra-sensitive pressure sensor based on graphene-nanoribbon (GNR) and investigate its electromechanical properties using classical molecular dynamics simulations and piezo-electricity theory. Since the top plate applied to the actual pressure is large whereas the contact area on the GNR is very small, both the sensitivity and the sensing range can be adjusted by controlling the aspect ratio between the top plate and the contact point areas. Our calculation shows that the electrical conductivity of GNRs can be tuned by the applied pressure and the electric conductance of the deflected GNR linearly increases with increasing applied pressure for the linear elastic region in low pressure below the cut-off point. In the curves for both the deflection and potential energy, the linear elastic regime in low pressure was explicitly separated with the non-linear elastic regime in high pressure. The proposed GNR-based nanoelectromechanical devices have great potential for application as electromechanical memory, relay or switching devices.

Superlubricity in nanoscale graphene structures has been of interest for developing graphene-based nanoelectromechanical systems, as well as for the study of basic mechanical properties. Here, we investigated the translational and rotational motions of a square graphene nanoflake with retracting motions by performing classical molecular dynamics simulations. Our results show that the kinetic energy of the translational motion was exchanged into the kinetic energy of the rotational motion. Thus, square graphene nanoflake oscillators have very low quality factors in translational motions. We discuss that square graphene nanoflakes have great potential to be a core component in nanoelectromechanical systems by detecting their motions with ultrahigh sensitivity to facilitate the development of sensor, memory, and quantum computing.

CdTe nanoribbons feature their unique optical properties compared with CdTe nanoparticles. Slow oxidation of tellurium ions on CdTe nanoparticles resulted in the organization of individual nanoparticle into nanoribbons. The light-controlled self-assembly of CdTe nanoparticles led to twisted ribbons. It was found that irradiation improved the oxidation of tellurium ions. Transmission electron microscopy (TEM) were performed to characterize the synthesized nanostructures and showed nanowires were twisted after self-assembly. The photoluminescence was slightly blue-shifted from 550 to 544 nm. This synthetic procedure could potentially provide a key step toward the fabrication of nanowires.

We investigated the tension and strain energy variations as a function of the axial strain in static conditions in graphene nanoribbon resonators and the resonance frequency change with tensile loading in dynamic conditions via classical molecular dynamics simulations. This theoretical study presents the application of graphene nanoribbon resonators tuned by tensile loading as ultrahigh frequency devices. The non-linear mechanical properties of the resonators were found, and for small axial strains, the mechanical properties of the graphene nanoribbon, such as strain-energy vs . axial-strain and frequency vs . strain or tension, were estimated by the classical continuum theory. The resonance frequencies increased with increasing axial strain, and such a relation could be regressed by a linearly increasing line on a log – log scale. The increasing resonance frequency due to increasing tension could be regressed by a square root function.

We investigated an ultrahigh sensitive accelerometer based on graphene nanoribbon resonators. Sensing acceleration can be made by their resonance frequency shift and/or their capacitance change. Schematics and the static properties were introduced and the dynamic properties were investigated via classical molecular dynamics simulation. As the acceleration increased, the oscillations of the deflections were going dramatically faster and the mean deflections increased, then the capacitance continually varied with large amplitudes and the resonance frequencies linearly increased in a log – log scale by power regression. The energy loss decreased with increasing time, and the average quality factors were dramatically reduced with increasing acceleration.

Ionic liquids (ILs) existing as liquid state at room temperature are composed of a immense heterocyclic cation and inorganic anion which is smaller than cation`s size. Thus, the species of cation and anion as well as the length of alkyl group on the cation have influence on their physical properties. Their outstanding properties such as non-volatility, thermal stability and wide range of electrochemical stability make these materials excellent candidates for green solvent which can substitute the conventional organic solvents. In this study, ILs based on imidazolium cation have been synthesized such as 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM] [Cl]), 1-butyl-3-methylimidazolium iodide ([BMIM][I]), and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][]). The density, viscosity, refractive index, heat capacity and ionic conductivity of [BMIM][Br], [BMIM][I], and [BMIM] [] were measured over range of temperature of 293.2 to 323.2 K. The density and refractive index values of [BMIM][I] were the highest among three ILs and the viscosity values of [BMIM][Br] were the highest among three ILs. The heat capacities [BMIM][] were higher than those of [BMIM][Br]. The ionic conductivities of [BMIM][] were higher than those of [BMIM][I].