- [Show abstract] [Hide abstract] ABSTRACT: 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 inhibition may arise from the prevention of methane-containing 5¹² cage formation by the ILs, inducing inhibition of metastable structure I hydrate formation.
- [Show abstract] [Hide abstract] ABSTRACT: Copper (Cu) nanoparticles (NPs) stabilized by morpholinium ionic liquids (ILs) were successfully synthesized via chemical reduction. N-(2-hydroxyethyl)-N-methyl-morpholinium chloride ([HEM-Mor][Cl]) and N-octyl-N-methyl-morpholinium chloride ([OMMor][Cl]) were synthesized and the products were verified by NMR spectroscopy. Transmission electron microscopy (TEM) was employed to characterize the metal NPs. The average sizes of the Cu NPs stabilized by [HEM-Mor][Cl] and [OMMor][Cl] were 4.1 nm and 4.3 nm, respectively. The structures of the produced particles were crystalline with a face-centered cubic (fcc) lattice. ILs were bound to the surfaces of the NPs, thereby protecting the particles from aggregation.
- [Show abstract] [Hide abstract] ABSTRACT: Graphene/carbon-nanotube (CNT) hybrid material can be useful in energy storage and nanoelectronic technologies. Here we address the CNT-oscillator encapsulated in a graphene-nanoribbon (GNR) trench as a novel design, and investigate its properties via classical molecular dynamics simulations. Since the energy barrier was very low while the CNT was encapsulated in the GNR trench, the CNT absorbed on the GNR surface could easily be encapsulated in the GNR trench. MD simulations showed that the CNT oscillator encapsulated in a GNR trench is compatible with simple CNT oscillators, so we anticipate that the CNT in GNR trench could work as an oscillator. So we can anticipate that the CNT encapsulated in a GNR trench can be applied to ultra-sensitive nanoelectromechanical oscillators, and this system has the possibility to be applied to relay-switching devices, and to shuttle memory.
- [Show abstract] [Hide abstract] ABSTRACT: Various ionic liquids (ILs) were tested as CH4 hydrate inhibitors with/without polymeric hydrate inhibitor, PVCap. Equilibrium dissociation conditions for CH4 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 CH4 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 CH4 hydrate inhibition behavior than did PVCap. The mixtures of PVCap and several ILs exhibited enhanced kinetic inhibition effects for CH4 hydrate formation.
- [Show abstract] [Hide abstract] ABSTRACT: 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 hydrate host framework at the surface by the hydrogen bonds of the ions with water molecules, which could promote the methane penetration or inclusion into the growing clathrate hydrate structures, thereby improving hydrate formation. In contrast, the kinetic hydrate inhibition behavior of HEMM-BF4 might be attributed to the hypothesis that BF4– could act as a mobile pseudoguest because the anion cannot be the guest of the hydrate cage owing to the charge imbalance even though it could fit into the structure I hydrate cages.
- [Show abstract] [Hide abstract] ABSTRACT: Novel hybrid nanostructures can be fabricated by encapsulating molecules within carbon nanotubes (CNTs). Here we used classical molecular dynamics (MD) simulations to investigate the dynamic properties of nonvolatile Bucky shuttle memory elements, based on C60 fullerene encapsulated in a partially opened CNT. Our MD simulations indicated bistability in the van der Waals potential energy as well as the position of change for the encapsulated C60 fullerene between its bistable positions. The C60 fullerene could retain its position without recharging due the presence of local potential wells. Our results showed that the proposed system has potential to operate as a non-volatile memory device, and these results further the understanding of new molecular machines based on carbon nanopeapods via their side opening.
- [Show abstract] [Hide abstract] ABSTRACT: Choline chloride (ChCl) is a well-known material forming deep eutectic solvents (DESs) when mixed with a hydrogen bonding donor (HBD). The potential applicability of DES systems is wide for replacing ionic liquids at relatively low cost. Therefore, the application to chemical processes necessitates the reliable data of DES properties. In this work, thermal behaviors of two ChCl-based DES systems (ChCl+urea and ChCl+1,3-dimethylurea) were investigated by using a differential scanning calorimeter. Crystalline as well as amorphous characteristics were found by varying compositions. In general, the increased composition of ChCl strengthened the crystallinity of solid phase. In the ChCl+urea system, a phase diagram was drawn with obtained melting point data while it could not be available for the other system.
- [Show abstract] [Hide abstract] ABSTRACT: 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 ([EMPip][BF4]) > N-ethyl-N-methylpiperidinium bromide ([EMPip][Br]) > N-ethyl-N-methylmorpholinium tetrafluoroborate ([EMMor][BF4]) > N-ethyl-N-methylmorpholinium bromide ([EMMor][Br]). The best among these ILs had inhibition effectiveness comparable with ethylene glycol and triethylene glycol, which are used commercially as THIs.
- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: Cadmium telluride (CdTe) nanowires were successfully synthesized from individual nanoparticles and the evolutionary process was investigated. Slow oxidation of Te2− in CdTe nanoparticles resulted in the generation of ribbons consisting of several layers of individual nanocrystals. The length of nanowires ranged from 1 to 8 μm. The presence of unusual shapes of multiparticle assemblies, such as bouquet, dog-bone, and ribbon bunches was observed as intermediate stages. The images of nanoribbons were analysed based on transmission electron microscopy and scanning electron microscopy. The suggested synthetic procedure provides a viable pathway for the fabrication of nanomaterials with helical conformations.
- [Show abstract] [Hide abstract] ABSTRACT: The equilibrium boundaries of CH4 and CO2 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 CH4 hydrate.
- [Show abstract] [Hide abstract] ABSTRACT: We propose schematics for an ultra-sensitive pressure sensor based on graphene and investigate its mechanical responses using classical molecular dynamics simulations. The top structure is similar to a thumbtack or pushpin and the bottom structure is composed of the graphene on the cylindrical hole. So while the top plate applied to the actual pressure has a large area, the majority of the load transfers to the graphene through the narrow pin. Therefore, the sensitivity can be greatly enhanced and the sensing limits can be adjusted by designing the aspect ratio between the head and the pin areas composed of the top structure. Simulation results for the operations of the proposed sensor were in good agreement with the previous experimental and theoretical works. This proposed schematics can detect the pressure via the deflection change or/and the resonance frequency shift, and also have great potential for versatile applications in nanoelectromechanical systems.
- [Show abstract] [Hide abstract] ABSTRACT: 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 ≥278.5K, 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 BF4-
- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: CdTe nanowires were synthesized from individual nanoparticles via self-assembly at a specific wavelength of light. The wavelength of 500 nm resulted in a self-assembly of nanoparticles into nanowires. Most of the produced nanowires were straight and long in shape and their length ranged from 300 nm to 20 μm. The oxidation of Te2– in CdTe nanoparticles under the visible light resulted in the assembly of nanowires consisting of several layers of individual nanoparticles. Transmission electron microscopy and scanning electron microscopy were performed to characterize the synthesized nanostructures. Energy-dispersive X-ray demonstrated the atomic percentage of nanowires. Photoluminescence showed that the wavelength of the nanostructures is slightly blue-shifted from 555 to 548 nm.
- [Show abstract] [Hide abstract] ABSTRACT: This paper presents the schematics and the energetics of nonvolatile-nanomemory-element based on carbon nanotube (CNT) on graphene nanoribbon (GNR) array using interatomic interaction potential function. The system proposed was composed of short outer CNT and long core CNT placed on two GNRs with a gap. The short outer CNT, which can be formed by electro-burning or electron-beam stripping, shuttles between two GNRs along the core CNT under the alternatively applied force fields. When the outer CNT settles on the GNRs, the local energy minima are achieved from the attractive van der Waals potential energies and then, since the outer CNT shuttle remains its position on the GNR without external force fields, the proposed system can operate a nonvolatile memory device. To switch this CNT shuttle system, the external force fields to overcome the restoring force exerted by van der Waals attractions should be applied.
- [Show abstract] [Hide abstract] ABSTRACT: We address the simple schematics of graphene-nanoflake shuttle-memory and investigate its energetic and dynamic properties. The internal dynamics of a related model system, consisting of a graphene-nanoflake on a patterned graphene nanoribbon, are investigated via classical molecular dynamics simulations. The van der Waals interactions between the graphene-nanoflake and the patterned graphene nanoribon make bistable potential energy wells in the larger surface area regions of the patterned graphene nanoribbon, and then the graphene-flake keeps its seat on one of the bistable positions, which is the place where the binary data is archived. This graphenenanoflake shuttle can be a tunable two-level system, where transitions between the bistable positions can be induced by applying an electric field. Nanostructures composed of graphene-nanoflake on graphene-nanoribbon are applicable to ultra-fast response oscillators, switches, sensors, and quantum computing, as well as nonvolatile memory.
- [Show abstract] [Hide abstract] ABSTRACT: 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.
Korea National University of Transportation
Sŏul, Seoul, South Korea
- Department of Chemical and Biology Engineering
Chungbuk National University
Chinsen, Chungcheongbuk-do, South Korea
- Department of Chemical Engineering
Korea Advanced Institute of Science and Technology
Seoul, Seoul, South Korea
- Department of Chemical and Biomolecular Engineering