Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2005
We report on molecular simulation studies of the ionic flow in the presence of charged carbon nan... more We report on molecular simulation studies of the ionic flow in the presence of charged carbon nanotubes. Our domain contains three species; viz. positively charged sodium ions, negatively charged chlorine ions and neutral water; and a pair of single-walled carbon nanotube electrodes. One of the nanotube is positively charged and the other is negatively charged. The system of 1024 atoms is initially allowed to equilibrate from an FCC crystal structure for the solution. The nanotubes are tethered and the carbon atoms are assumed to vibrate as in a One-Dimensional Harmonic Oscillator (ODHO) about their mean positions. The sodium ions travel towards the negatively charged carbon nanotube and the chlorine ions likewise flow towards the positively charged nanotube. The simulation uses a Lennard-Jones soft sphere potential model and coulombic potential for interaction between the charges. In addition to the ion transport mechanism, the hydrophobic character of carbon nanotubes is clearly evident from the simulated flow.
The journal of physical chemistry. B, Jan 21, 2016
This paper presents the computational assessment of the electrochemical stability of a series of ... more This paper presents the computational assessment of the electrochemical stability of a series of alkyl methylimidazolium-based ionic liquids for their use as lithium battery electrolytes. The oxidation and reduction potentials of the constituent cation and anion of each ionic liquid with respect to a Li(+)/Li reference electrode were calculated using density functional theory following the method of thermodynamic cycles, and the electrochemical stability windows (ESW)s of these ionic liquids were obtained. The effect of varying the length of alkyl side chains of the methylimidazolium-based cations on the redox potentials and ESWs was investigated. The results show that the limits of the ESWs of these methylimidazolium-based ionic liquids are defined by the oxidation potential of the anions and the reduction potential of alkyl-methylimidazolium cations. Moreover, ionic liquids with [PF6](-) anion have a wider ESW. In addition to characterizing structure-function relationships, the ac...
We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liq... more We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liquid-vapor Ar mixtures adjacent to warmer Fe walls. The equilibration of the system towards a uniform overall temperature is investigated using nonequilibrium molecular dynamics simulations from which the heat flux is also determined explicitly. The Ar-Fe intermolecular interactions induce the migration of fluid atoms into quasicrystalline interfacial layers adjacent to the walls, creating vacancies at the migration sites. This induces temperature discontinuities between the solidlike interfaces and their neighboring fluid molecules. The interfacial temperature difference and thus the heat flux decrease as the system equilibrates over time. The averaged interfacial thermal resistance Rk ,av decreases as the imposed wall temperature Tw is increased, as Rk ,av∝Tw-4.8. The simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity.
We investigate the hydrogen adsorbing characteristics of single-walled carbon nanotubes (CNTs) th... more We investigate the hydrogen adsorbing characteristics of single-walled carbon nanotubes (CNTs) through fundamental molecular dynamics simulations that characterize the role of ambient pressure and temperature, the presence of surface charges on the CNTs, inclusion of metal ion interconnects, and nanocapillary effects. While the literature suggests that hydrogen spillover due to the presence of metallic contaminants enhances storage on and inside the nanotubes, we find this to be significant for alkali and not transition metals. Charging the CNT surfaces does not significantly enhance hydrogen storage. We find that the bulk of the hydrogen storage occurs inside CNTs due to their nanocapillarity effect. Storage is much more dependent on external thermodynamic conditions such as the temperature and the pressure than on these facets of the CNT structure. The dependence of storage on the external thermodynamic conditions is analyzed and the optimal range of operating conditions is identified.
Li-air cell operated with ionic liquid electrolytes is a very promising energy storage technology... more Li-air cell operated with ionic liquid electrolytes is a very promising energy storage technology for electric vehicle and plug-in hybrid electric vehicle due to several favorable characteristics of ionic liquids. However, Li-air cells that employ room temperature ionic liquid (RTIL) electrolytes exhibit poor performance due to limited oxygen solubility and low reactant species mobility. To circumvent these aforementioned drawbacks, we investigated the electrical performance of a Li-air cell with ionic liquid electrolytes operating at high temperature. A continuum based model is used to quantify the performance of the Li-air cell, with an ionic liquid (MPPY-TFSI) electrolyte, as a function of operating temperature. Simulations at the atomistic scale, such as molecular dynamics (MD) and density functional theory (DFT) calculations are used to obtain key properties for the continuum model. These properties include electron transfer reaction rate constant, species diffusivity and oxygen solubility. The MD simulations indicate that oxygen solubility in ionic liquid increases with temperature, which is very favorable for high temperature operation. The continuum based cell level simulation results show that the battery performance can be improved significantly by increasing operating temperature. For instance, specific capacity as high as 3000 mAh/g can be achieved at 110 °C operating temperature, which is almost 25 times higher than its counterpart at room temperature. Simulation results also reveal that by increasing the operating temperature, the specific capacity can be improved significantly for high load current density, which is one of the most critical drawbacks in RTIL based Li-air battery. We also studied the effect of cathode thickness on the performance of Li-air battery at different operating temperatures. The transport limitation of oxygen and lithium ions can be alleviated at higher operating temperatures, suggesting that even thicker cathode materials can be used to enhance the cell capacity at elevated temperature.
Volume 2: Advanced Electronics and Photonics, Packaging Materials and Processing; Advanced Electronics and Photonics: Packaging, Interconnect and Reliability; Fundamentals of Thermal and Fluid Transport in Nano, Micro, and Mini Scales, 2015
We investigate the hydrogen storage potential of carbon nanotubes (CNTS) through fundamental mole... more We investigate the hydrogen storage potential of carbon nanotubes (CNTS) through fundamental molecular dynamics (MD) simulations. We suggest possible changes in the structure and conditions of CNTS that could enhance their storage capacity. Our parametric investigation involves ...
We present a multiscale model, based on molecular dynamics (MD) and kinetic Monte Carlo (kMC), to... more We present a multiscale model, based on molecular dynamics (MD) and kinetic Monte Carlo (kMC), to study the aggregation driven growth of colloidal particles. Coarse-grained molecular dynamics (CGMD) simulations are employed to detect key agglomeration events and calculate the corresponding rate constants. The kMC simulations employ these rate constants in a stochastic framework to track the growth of the agglomerates over longer time scales and length scales. One of the hallmarks of the model is a unique methodology to detect and characterize agglomeration events. The model accounts for individual cluster-scale effects such as change in size due to aggregation as well as local molecular-scale effects such as changes in the number of neighbors of each molecule in a colloidal cluster. Such definition of agglomeration events allows us to grow the cluster to sizes that are inaccessible to molecular simulations as well as track the shape of the growing cluster. A well-studied system, comprising fullerenes in NaCl electrolyte solution, was simulated to validate the model. Under the simulated conditions, the agglomeration process evolves from a diffusion limited cluster aggregation (DLCA) regime to percolating cluster in transition and finally to a gelation regime. Overall the data from the multiscale numerical model shows good agreement with existing theory of colloidal particle growth. Although in the present study we validated our model by specifically simulating fullerene agglomeration in electrolyte solution, the model is versatile and can be applied to a wide range of colloidal systems.
ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B, 2006
This paper focuses on the use of carbon nanotubes (CNT) for ion separation and encapsulation from... more This paper focuses on the use of carbon nanotubes (CNT) for ion separation and encapsulation from a solution containing both positive and negatively charged ions. Metal ion separation from drinking water or during material processing applications can be an important issue. We ...
ABSTRACT Ionic liquids are widely considered as potential electrolytes for lithium batteries due ... more ABSTRACT Ionic liquids are widely considered as potential electrolytes for lithium batteries due to their tunable electrochemical properties. In the present study, the mobility and transport characteristics of lithium ions in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (mppy+TFSI–) ionic liquids were characterized using the molecular dynamics method. Results from the simulations indicate that inclusion of organic additives such as ethylene carbonate, vinylene carbonate, and tetrahydrofuran decreases the extent of coordination of the lithium ion with the anion of the ionic liquid and hence increases its mobility and overall ionic conductivity. The mobility of lithium ions in the ionic liquid based electrolyte increases with increasing concentration of the additive. Of the additives investigated, ethylene carbonate was identified as the most effective in increasing the mobility of lithium ions, while vinylene carbonate increases the overall ionic conductivity to the greatest extent.
ABSTRACT Thin films of aligned carbon nanotubes (CNTs) have several interesting properties includ... more ABSTRACT Thin films of aligned carbon nanotubes (CNTs) have several interesting properties including the ability to transport ions, electrons, and thermal energy. The current study employed molecular dynamics (MD) simulations to determine the effect of varying functionalization topologies of CNTs on their deposition characteristics under applied electric fields of varying strength. The results indicate that the dynamics of CNT alignment along the direction of applied electric field is relatively faster and smoother in case of pristine CNTs compared to that of functionalized CNTs. Considering CNTs of identical length, pristine CNTs are aligned the closest to the direction of the electric field followed by side-functionalized and end-functionalized CNTs with the total alignment time being roughly similar. With increase in the strength of electric field, E, total alignment time decreases and is inversely proportional to E2. The final alignment angle (θ∞) and extent of oscillatory response in the case of side- and end-functionalized CNTs are diminished. In contrast with the alignment dynamics, the migration dynamics of pristine CNTs, which tend to agglomerate, is slower and shows some discontinuity compared to the functionalized CNTs. Analysis of the final structure of the deposited CNTs indicate that side-functionalized CNTs produce the most uniformly aligned deposit at relatively weaker electric fields followed by end-functionalized, and pristine CNTs, due partly to their greater extent of solvation, and are therefore a better choice for deposition of uniform CNT films on substrates.
Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2005
We report on molecular simulation studies of the ionic flow in the presence of charged carbon nan... more We report on molecular simulation studies of the ionic flow in the presence of charged carbon nanotubes. Our domain contains three species; viz. positively charged sodium ions, negatively charged chlorine ions and neutral water; and a pair of single-walled carbon nanotube electrodes. One of the nanotube is positively charged and the other is negatively charged. The system of 1024 atoms is initially allowed to equilibrate from an FCC crystal structure for the solution. The nanotubes are tethered and the carbon atoms are assumed to vibrate as in a One-Dimensional Harmonic Oscillator (ODHO) about their mean positions. The sodium ions travel towards the negatively charged carbon nanotube and the chlorine ions likewise flow towards the positively charged nanotube. The simulation uses a Lennard-Jones soft sphere potential model and coulombic potential for interaction between the charges. In addition to the ion transport mechanism, the hydrophobic character of carbon nanotubes is clearly evident from the simulated flow.
The journal of physical chemistry. B, Jan 21, 2016
This paper presents the computational assessment of the electrochemical stability of a series of ... more This paper presents the computational assessment of the electrochemical stability of a series of alkyl methylimidazolium-based ionic liquids for their use as lithium battery electrolytes. The oxidation and reduction potentials of the constituent cation and anion of each ionic liquid with respect to a Li(+)/Li reference electrode were calculated using density functional theory following the method of thermodynamic cycles, and the electrochemical stability windows (ESW)s of these ionic liquids were obtained. The effect of varying the length of alkyl side chains of the methylimidazolium-based cations on the redox potentials and ESWs was investigated. The results show that the limits of the ESWs of these methylimidazolium-based ionic liquids are defined by the oxidation potential of the anions and the reduction potential of alkyl-methylimidazolium cations. Moreover, ionic liquids with [PF6](-) anion have a wider ESW. In addition to characterizing structure-function relationships, the ac...
We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liq... more We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liquid-vapor Ar mixtures adjacent to warmer Fe walls. The equilibration of the system towards a uniform overall temperature is investigated using nonequilibrium molecular dynamics simulations from which the heat flux is also determined explicitly. The Ar-Fe intermolecular interactions induce the migration of fluid atoms into quasicrystalline interfacial layers adjacent to the walls, creating vacancies at the migration sites. This induces temperature discontinuities between the solidlike interfaces and their neighboring fluid molecules. The interfacial temperature difference and thus the heat flux decrease as the system equilibrates over time. The averaged interfacial thermal resistance Rk ,av decreases as the imposed wall temperature Tw is increased, as Rk ,av∝Tw-4.8. The simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity.
We investigate the hydrogen adsorbing characteristics of single-walled carbon nanotubes (CNTs) th... more We investigate the hydrogen adsorbing characteristics of single-walled carbon nanotubes (CNTs) through fundamental molecular dynamics simulations that characterize the role of ambient pressure and temperature, the presence of surface charges on the CNTs, inclusion of metal ion interconnects, and nanocapillary effects. While the literature suggests that hydrogen spillover due to the presence of metallic contaminants enhances storage on and inside the nanotubes, we find this to be significant for alkali and not transition metals. Charging the CNT surfaces does not significantly enhance hydrogen storage. We find that the bulk of the hydrogen storage occurs inside CNTs due to their nanocapillarity effect. Storage is much more dependent on external thermodynamic conditions such as the temperature and the pressure than on these facets of the CNT structure. The dependence of storage on the external thermodynamic conditions is analyzed and the optimal range of operating conditions is identified.
Li-air cell operated with ionic liquid electrolytes is a very promising energy storage technology... more Li-air cell operated with ionic liquid electrolytes is a very promising energy storage technology for electric vehicle and plug-in hybrid electric vehicle due to several favorable characteristics of ionic liquids. However, Li-air cells that employ room temperature ionic liquid (RTIL) electrolytes exhibit poor performance due to limited oxygen solubility and low reactant species mobility. To circumvent these aforementioned drawbacks, we investigated the electrical performance of a Li-air cell with ionic liquid electrolytes operating at high temperature. A continuum based model is used to quantify the performance of the Li-air cell, with an ionic liquid (MPPY-TFSI) electrolyte, as a function of operating temperature. Simulations at the atomistic scale, such as molecular dynamics (MD) and density functional theory (DFT) calculations are used to obtain key properties for the continuum model. These properties include electron transfer reaction rate constant, species diffusivity and oxygen solubility. The MD simulations indicate that oxygen solubility in ionic liquid increases with temperature, which is very favorable for high temperature operation. The continuum based cell level simulation results show that the battery performance can be improved significantly by increasing operating temperature. For instance, specific capacity as high as 3000 mAh/g can be achieved at 110 °C operating temperature, which is almost 25 times higher than its counterpart at room temperature. Simulation results also reveal that by increasing the operating temperature, the specific capacity can be improved significantly for high load current density, which is one of the most critical drawbacks in RTIL based Li-air battery. We also studied the effect of cathode thickness on the performance of Li-air battery at different operating temperatures. The transport limitation of oxygen and lithium ions can be alleviated at higher operating temperatures, suggesting that even thicker cathode materials can be used to enhance the cell capacity at elevated temperature.
Volume 2: Advanced Electronics and Photonics, Packaging Materials and Processing; Advanced Electronics and Photonics: Packaging, Interconnect and Reliability; Fundamentals of Thermal and Fluid Transport in Nano, Micro, and Mini Scales, 2015
We investigate the hydrogen storage potential of carbon nanotubes (CNTS) through fundamental mole... more We investigate the hydrogen storage potential of carbon nanotubes (CNTS) through fundamental molecular dynamics (MD) simulations. We suggest possible changes in the structure and conditions of CNTS that could enhance their storage capacity. Our parametric investigation involves ...
We present a multiscale model, based on molecular dynamics (MD) and kinetic Monte Carlo (kMC), to... more We present a multiscale model, based on molecular dynamics (MD) and kinetic Monte Carlo (kMC), to study the aggregation driven growth of colloidal particles. Coarse-grained molecular dynamics (CGMD) simulations are employed to detect key agglomeration events and calculate the corresponding rate constants. The kMC simulations employ these rate constants in a stochastic framework to track the growth of the agglomerates over longer time scales and length scales. One of the hallmarks of the model is a unique methodology to detect and characterize agglomeration events. The model accounts for individual cluster-scale effects such as change in size due to aggregation as well as local molecular-scale effects such as changes in the number of neighbors of each molecule in a colloidal cluster. Such definition of agglomeration events allows us to grow the cluster to sizes that are inaccessible to molecular simulations as well as track the shape of the growing cluster. A well-studied system, comprising fullerenes in NaCl electrolyte solution, was simulated to validate the model. Under the simulated conditions, the agglomeration process evolves from a diffusion limited cluster aggregation (DLCA) regime to percolating cluster in transition and finally to a gelation regime. Overall the data from the multiscale numerical model shows good agreement with existing theory of colloidal particle growth. Although in the present study we validated our model by specifically simulating fullerene agglomeration in electrolyte solution, the model is versatile and can be applied to a wide range of colloidal systems.
ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B, 2006
This paper focuses on the use of carbon nanotubes (CNT) for ion separation and encapsulation from... more This paper focuses on the use of carbon nanotubes (CNT) for ion separation and encapsulation from a solution containing both positive and negatively charged ions. Metal ion separation from drinking water or during material processing applications can be an important issue. We ...
ABSTRACT Ionic liquids are widely considered as potential electrolytes for lithium batteries due ... more ABSTRACT Ionic liquids are widely considered as potential electrolytes for lithium batteries due to their tunable electrochemical properties. In the present study, the mobility and transport characteristics of lithium ions in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (mppy+TFSI–) ionic liquids were characterized using the molecular dynamics method. Results from the simulations indicate that inclusion of organic additives such as ethylene carbonate, vinylene carbonate, and tetrahydrofuran decreases the extent of coordination of the lithium ion with the anion of the ionic liquid and hence increases its mobility and overall ionic conductivity. The mobility of lithium ions in the ionic liquid based electrolyte increases with increasing concentration of the additive. Of the additives investigated, ethylene carbonate was identified as the most effective in increasing the mobility of lithium ions, while vinylene carbonate increases the overall ionic conductivity to the greatest extent.
ABSTRACT Thin films of aligned carbon nanotubes (CNTs) have several interesting properties includ... more ABSTRACT Thin films of aligned carbon nanotubes (CNTs) have several interesting properties including the ability to transport ions, electrons, and thermal energy. The current study employed molecular dynamics (MD) simulations to determine the effect of varying functionalization topologies of CNTs on their deposition characteristics under applied electric fields of varying strength. The results indicate that the dynamics of CNT alignment along the direction of applied electric field is relatively faster and smoother in case of pristine CNTs compared to that of functionalized CNTs. Considering CNTs of identical length, pristine CNTs are aligned the closest to the direction of the electric field followed by side-functionalized and end-functionalized CNTs with the total alignment time being roughly similar. With increase in the strength of electric field, E, total alignment time decreases and is inversely proportional to E2. The final alignment angle (θ∞) and extent of oscillatory response in the case of side- and end-functionalized CNTs are diminished. In contrast with the alignment dynamics, the migration dynamics of pristine CNTs, which tend to agglomerate, is slower and shows some discontinuity compared to the functionalized CNTs. Analysis of the final structure of the deposited CNTs indicate that side-functionalized CNTs produce the most uniformly aligned deposit at relatively weaker electric fields followed by end-functionalized, and pristine CNTs, due partly to their greater extent of solvation, and are therefore a better choice for deposition of uniform CNT films on substrates.
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Papers by Soumik Banerjee