Raghavan Ranganathan - Academia.edu (original) (raw)

Papers by Raghavan Ranganathan

Research paper thumbnail of Vacancy Rich TiB<sub>2</sub> Nanosheets Promote Electrochemical Ammonia Synthesis

ACS applied materials & interfaces, May 2, 2024

Research paper thumbnail of Recent advances in modelling structure-property correlations in high-entropy alloys

Journal of Materials Science and Technology/Journal of materials science & technology, Apr 1, 2024

Research paper thumbnail of Mechanical and Viscoelastic Properties of Stacked and Grafted Graphene/Graphene Oxide–Polyethylene Nanocomposites: A Coarse-Grained Molecular Dynamics Study

Research paper thumbnail of Competing mechanisms govern the thermal rectification behavior in semi-stochastic polycrystalline graphene with graded grain-size distribution

Research paper thumbnail of Nitrogen adsorption via charge transfer on vacancies created during surfactant assisted exfoliation of TiB2

Nanoscale

Titanium diboride (TiB2), a layered ceramic material, comprised of titanium atoms sandwiched in b... more Titanium diboride (TiB2), a layered ceramic material, comprised of titanium atoms sandwiched in between honeycomb planes of boron atoms, exhibits a promising structure to utilize the rich chemistry offered by the synergy of titanium and boron.

Research paper thumbnail of Superior Protection Conferred by Multi-Layered Graphene–Polyethylene Nanocomposites under Shock Loading

ACS Applied Engineering Materials, Dec 25, 2023

Research paper thumbnail of Viscoelastic damping in crystalline composites and alloys

Bulletin of the American Physical Society, Mar 16, 2016

Submitted for the MAR16 Meeting of The American Physical Society Viscoelastic damping in crystall... more Submitted for the MAR16 Meeting of The American Physical Society Viscoelastic damping in crystalline composites and alloys RAGHA-VAN RANGANATHAN, RAHMI OZISIK, PAWEL KEBLINSKI, Rensselaer Polytech Inst-We use molecular dynamics simulations to study viscoelastic behavior of model Lennard-Jones (LJ) crystalline composites subject to an oscillatory shear deformation. The two crystals, namely a soft and a stiff phase, individually show highly elastic behavior and a very small loss modulus. On the other hand, when the stiff phase is included within the soft matrix as a sphere, the composite exhibits significant viscoelastic damping and a large phase shift between stress and strain. In fact, the maximum loss modulus in these model composites was found to be about 20 times greater than that given by the theoretical Hashin-Shtrikman upper bound. We attribute this behavior to the fact that in composites shear strain is highly inhomogeneous and mostly accommodated by the soft phase, corroborated by frequency-dependent Grüneisen parameter analysis. Interestingly, the frequency at which the damping is greatest scales with the microstructural length scale of the composite. Finally, a critical comparison between damping properties of these composites with ordered and disordered alloys and superlattice structures is made.

Research paper thumbnail of Viscoelastic and Dynamic Properties of Well-Mixed and Phase-Separated Binary Polymer Blends: A Molecular Dynamics Simulation Study

Macromolecules, Aug 1, 2017

The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend... more The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend are studied via molecular dynamics simulations. The model blend system is made up of two chain types having a large glass transition temperature (T g) difference and presents two blend morphologies: a well-mixed, homogeneous blend and a phase-separated blend. These two morphologies represent dynamically coupled and dynamically confined states. The well-mixed, homogeneous blend exhibited greater storage modulus and slower low-T g matrix chain dynamics compared to the phase-separated blend. The influence of various system parameters, such as high-T g chain length and (volume) concentration, and shear frequency on various static, dynamic, and viscoelastic properties is investigated to identify the source of the observed stiffening in the well-mixed, homogeneous blends.

Research paper thumbnail of Competing mechanisms govern the thermal rectification behavior in semi-stochastic polycrystalline graphene with graded grain-density distribution

arXiv (Cornell University), Jul 24, 2023

Thermal rectifiers are devices that have different thermal conductivities in opposing directions ... more Thermal rectifiers are devices that have different thermal conductivities in opposing directions of heat flow. The realization of practical thermal rectifiers relies significantly on a sound understanding of the underlying mechanisms of asymmetric heat transport, and two-dimensional materials offer a promising opportunity in this regard owing to their simplistic structures together with a vast possibility of tunable imperfections. However, the in-plane thermal rectification mechanisms in 2D materials like graphene having directional gradients of grain sizes have remained elusive. In fact, understanding the heat transport mechanisms in polycrystalline graphene, which are more practical to synthesize than large-scale singlecrystal graphene, could potentially allow a unique opportunity, in principle, to combine with other defects and designs for effective optimization of thermal rectification. In this work, we investigate the thermal rectification behavior in periodic atomistic models of polycrystalline graphene whose grain arrangements were generated semi-stochastically to have different gradient grain-density distributions along the in-plane heat flow direction. We employ the centroidal Voronoi tessellation technique to generate realistic grain boundary structures for graphene, and the non-equilibrium molecular dynamics simulations method is used to calculate the thermal conductivities and rectification values. Additionally, detailed phonon characteristics and propagating phonon spatial energy densities are analyzed based on the fluctuationdissipation theory to elucidate the competitive interplay between two underlying mechanisms, namely, (i) propagating phonon coupling and (ii) temperature-dependence of thermal conductivity that determines the degree of asymmetric heat flow in graded polycrystalline graphene.

Research paper thumbnail of Viscoelastic damping in crystalline composites: A molecular dynamics study

Composites Part B-engineering, May 1, 2016

Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jon... more Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jones (LJ) crystalline composites subject to an oscillatory shear deformation. The two crystals, namely a soft and a stiff phase, individually show highly elastic behavior and very small loss modulus. On the other hand, when the stiff phase is included within the soft matrix as a sphere, the composite exhibits significant viscous damping and a large phase shift between stress and strain. In fact, the maximum loss modulus in these model composites was found to be about 20 times greater than that given by the theoretical Hashin-Shtrikman upper bound. We attribute this behavior to the fact that in composites shear strain is highly inhomogeneous and mostly accommodated by the soft phase. This is corroborated by mode-dependent Grüneisen parameter analysis showing that in the low frequency regime, Grüneisen parameters, which measure degree of anharmonicity, are about twice greater for the composite than each individual homogenous crystal. Interestingly, the frequency at which the damping is greatest scales with the microstructural length scale of the composite, a feature we also observe for superlattice structures.

Research paper thumbnail of Generation of amorphous carbon models using liquid quench method: A reactive molecular dynamics study

Carbon, Mar 1, 2017

Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of ... more Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of amorphous carbon (a-C) at a wide range of densities (from 0.5 g/cc to 3.2 g/cc) via the "liquid-quench" method. A systematic study is undertaken to characterize the structural features of the resulting a-C models as a function of carbon density and liquid quench simulation conditions: quench rate, type of quench (linear or exponential), annealing time and size of simulation box. The structural features of the models are investigated in terms of pair correlation functions, bond-angles, pore-size distribution and carbon hybridization content. Further, the influence of quench conditions on hybridization/graphitization is investigated for different stages of the simulation. We observe that the structural features of generated a-carbon models agree well with similar models reported in literature. We find that in the low-density regime, size

Research paper thumbnail of Modeling high-temperature diffusion of gases in micro and mesoporous amorphous carbon

Journal of Chemical Physics, Aug 24, 2015

In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using e... more In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using equilibrium molecular dynamics simulations. Microporous and mesoporous carbon structures are computationally generated using liquid quench method and reactive force fields. Motivated by the need to understand high temperature diffusivity of light weight gases like H 2 , O 2 , H 2 O, and CO in amorphous carbon, we investigate the diffusion behavior as function of two important parameters: (a) the pore size and (b) the concentration of diffusing gases. The effect of pore size on diffusion is studied by employing multiple realizations of the amorphous carbon structures in microporous and mesoporous regimes, corresponding to densities of 1 g/cm 3 and 0.5 g/cm 3 , respectively. A detailed analysis of the effect of gas concentration on diffusion in the context of these two porosity regimes is presented. For the microporous structure, we observe that predominantly, a high diffusivity results when the structure is highly anisotropic and contains wide channels between the pores. On the other hand, when the structure is highly homogeneous, significant molecule-wall scattering leads to a nearly concentration-independent behavior of diffusion (reminiscent of Knudsen diffusion). The mesoporous regime is similar in behavior to the highly diffusive microporous carbon case in that diffusion at high concentration is governed by gas-gas collisions (reminiscent of Fickian diffusion), which transitions to a Knudsen-like diffusion at lower concentration.

Research paper thumbnail of Competing mechanisms govern the thermal rectification behavior in semi-stochastic polycrystalline graphene with graded grain-density distribution

Thermal rectifiers are devices that have different thermal conductivities in opposing directions ... more Thermal rectifiers are devices that have different thermal conductivities in opposing directions of heat flow. The realization of practical thermal rectifiers relies significantly on a sound understanding of the underlying mechanisms of asymmetric heat transport, and two-dimensional materials offer a promising opportunity in this regard owing to their simplistic structures together with a vast possibility of tunable imperfections. However, the in-plane thermal rectification mechanisms in 2D materials like graphene having directional gradients of grain sizes have remained elusive. In fact, understanding the heat transport mechanisms in polycrystalline graphene, which are more practical to synthesize than large-scale single-crystal graphene, could potentially allow a unique opportunity, in principle, to combine with other defects and designs for effective optimization of thermal rectification. In this work, we investigate the thermal rectification behavior in periodic atomistic models...

Research paper thumbnail of Does the doping strategy of ferrite nanoparticles create a correlation between reactivity and toxicity?

Environmental Science: Nano

The doping strategy of ferrite nanoparticles induced a correlation between their reactivity and t... more The doping strategy of ferrite nanoparticles induced a correlation between their reactivity and toxicity. The evidence showed the induction of biological responses as a factor of their dissolution and suspension properties of ferrite nanoparticles.

Research paper thumbnail of A Generative Approach to Materials Discovery, Design, and Optimization

Research paper thumbnail of Viscoelastic and Dynamic Properties of Well-Mixed and Phase-Separated Binary Polymer Blends: A Molecular Dynamics Simulation Study

Macromolecules, 2017

The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend... more The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend are studied via molecular dynamics simulations. The model blend system is made up of two chain types having a large glass transition temperature (T g) difference and presents two blend morphologies: a well-mixed, homogeneous blend and a phase-separated blend. These two morphologies represent dynamically coupled and dynamically confined states. The well-mixed, homogeneous blend exhibited greater storage modulus and slower low-T g matrix chain dynamics compared to the phase-separated blend. The influence of various system parameters, such as high-T g chain length and (volume) concentration, and shear frequency on various static, dynamic, and viscoelastic properties is investigated to identify the source of the observed stiffening in the well-mixed, homogeneous blends.

Research paper thumbnail of Generation of amorphous carbon models using liquid quench method: A reactive molecular dynamics study

Carbon, 2017

Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of ... more Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of amorphous carbon (a-C) at a wide range of densities (from 0.5 g/cc to 3.2 g/cc) via the "liquid-quench" method. A systematic study is undertaken to characterize the structural features of the resulting a-C models as a function of carbon density and liquid quench simulation conditions: quench rate, type of quench (linear or exponential), annealing time and size of simulation box. The structural features of the models are investigated in terms of pair correlation functions, bond-angles, pore-size distribution and carbon hybridization content. Further, the influence of quench conditions on hybridization/graphitization is investigated for different stages of the simulation. We observe that the structural features of generated a-carbon models agree well with similar models reported in literature. We find that in the low-density regime, size

Research paper thumbnail of Viscoelastic damping in crystalline composites: A molecular dynamics study

Composites Part B: Engineering, 2016

Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jon... more Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jones (LJ) crystalline composites subject to an oscillatory shear deformation. The two crystals, namely a soft and a stiff phase, individually show highly elastic behavior and very small loss modulus. On the other hand, when the stiff phase is included within the soft matrix as a sphere, the composite exhibits significant viscous damping and a large phase shift between stress and strain. In fact, the maximum loss modulus in these model composites was found to be about 20 times greater than that given by the theoretical Hashin-Shtrikman upper bound. We attribute this behavior to the fact that in composites shear strain is highly inhomogeneous and mostly accommodated by the soft phase. This is corroborated by mode-dependent Grüneisen parameter analysis showing that in the low frequency regime, Grüneisen parameters, which measure degree of anharmonicity, are about twice greater for the composite than each individual homogenous crystal. Interestingly, the frequency at which the damping is greatest scales with the microstructural length scale of the composite, a feature we also observe for superlattice structures.

Research paper thumbnail of Modeling high-temperature diffusion of gases in micro and mesoporous amorphous carbon

The Journal of chemical physics, Jan 28, 2015

In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using e... more In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using equilibrium molecular dynamics simulations. Microporous and mesoporous carbon structures are computationally generated using liquid quench method and reactive force fields. Motivated by the need to understand high temperature diffusivity of light weight gases like H2, O2, H2O, and CO in amorphous carbon, we investigate the diffusion behavior as function of two important parameters: (a) the pore size and (b) the concentration of diffusing gases. The effect of pore size on diffusion is studied by employing multiple realizations of the amorphous carbon structures in microporous and mesoporous regimes, corresponding to densities of 1 g/cm(3) and 0.5 g/cm(3), respectively. A detailed analysis of the effect of gas concentration on diffusion in the context of these two porosity regimes is presented. For the microporous structure, we observe that predominantly, a high diffusivity results when the...

Research paper thumbnail of Tensile and Viscoelastic Behavior in Nacre-Inspired Nanocomposites: A Coarse-Grained Molecular Dynamics Study

Nanomaterials

Organisms hold an extraordinarily evolutionary advantage in forming complex, hierarchical structu... more Organisms hold an extraordinarily evolutionary advantage in forming complex, hierarchical structures across different length scales that exhibit superior mechanical properties. Mimicking these structures for synthesizing high-performance materials has long held a fascination and has seen rapid growth in the recent past thanks to high-resolution microscopy, design, synthesis, and testing methodologies. Among the class of natural materials, nacre, found in mollusk shells, exhibits remarkably high mechanical strength and toughness. The highly organized “brick and mortar” structure at different length scales is a basis for excellent mechanical properties and the capability to dissipate energy and propagation in nacre. Here, we employ large-scale atomistic coarse-grained molecular dynamics simulations to study the mechanical and viscoelastic behavior of nacre-like microstructures. Uniaxial tension and oscillatory shear simulations were performed to gain insight into the role of complex s...

Research paper thumbnail of Vacancy Rich TiB<sub>2</sub> Nanosheets Promote Electrochemical Ammonia Synthesis

ACS applied materials & interfaces, May 2, 2024

Research paper thumbnail of Recent advances in modelling structure-property correlations in high-entropy alloys

Journal of Materials Science and Technology/Journal of materials science & technology, Apr 1, 2024

Research paper thumbnail of Mechanical and Viscoelastic Properties of Stacked and Grafted Graphene/Graphene Oxide–Polyethylene Nanocomposites: A Coarse-Grained Molecular Dynamics Study

Research paper thumbnail of Competing mechanisms govern the thermal rectification behavior in semi-stochastic polycrystalline graphene with graded grain-size distribution

Research paper thumbnail of Nitrogen adsorption via charge transfer on vacancies created during surfactant assisted exfoliation of TiB2

Nanoscale

Titanium diboride (TiB2), a layered ceramic material, comprised of titanium atoms sandwiched in b... more Titanium diboride (TiB2), a layered ceramic material, comprised of titanium atoms sandwiched in between honeycomb planes of boron atoms, exhibits a promising structure to utilize the rich chemistry offered by the synergy of titanium and boron.

Research paper thumbnail of Superior Protection Conferred by Multi-Layered Graphene–Polyethylene Nanocomposites under Shock Loading

ACS Applied Engineering Materials, Dec 25, 2023

Research paper thumbnail of Viscoelastic damping in crystalline composites and alloys

Bulletin of the American Physical Society, Mar 16, 2016

Submitted for the MAR16 Meeting of The American Physical Society Viscoelastic damping in crystall... more Submitted for the MAR16 Meeting of The American Physical Society Viscoelastic damping in crystalline composites and alloys RAGHA-VAN RANGANATHAN, RAHMI OZISIK, PAWEL KEBLINSKI, Rensselaer Polytech Inst-We use molecular dynamics simulations to study viscoelastic behavior of model Lennard-Jones (LJ) crystalline composites subject to an oscillatory shear deformation. The two crystals, namely a soft and a stiff phase, individually show highly elastic behavior and a very small loss modulus. On the other hand, when the stiff phase is included within the soft matrix as a sphere, the composite exhibits significant viscoelastic damping and a large phase shift between stress and strain. In fact, the maximum loss modulus in these model composites was found to be about 20 times greater than that given by the theoretical Hashin-Shtrikman upper bound. We attribute this behavior to the fact that in composites shear strain is highly inhomogeneous and mostly accommodated by the soft phase, corroborated by frequency-dependent Grüneisen parameter analysis. Interestingly, the frequency at which the damping is greatest scales with the microstructural length scale of the composite. Finally, a critical comparison between damping properties of these composites with ordered and disordered alloys and superlattice structures is made.

Research paper thumbnail of Viscoelastic and Dynamic Properties of Well-Mixed and Phase-Separated Binary Polymer Blends: A Molecular Dynamics Simulation Study

Macromolecules, Aug 1, 2017

The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend... more The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend are studied via molecular dynamics simulations. The model blend system is made up of two chain types having a large glass transition temperature (T g) difference and presents two blend morphologies: a well-mixed, homogeneous blend and a phase-separated blend. These two morphologies represent dynamically coupled and dynamically confined states. The well-mixed, homogeneous blend exhibited greater storage modulus and slower low-T g matrix chain dynamics compared to the phase-separated blend. The influence of various system parameters, such as high-T g chain length and (volume) concentration, and shear frequency on various static, dynamic, and viscoelastic properties is investigated to identify the source of the observed stiffening in the well-mixed, homogeneous blends.

Research paper thumbnail of Competing mechanisms govern the thermal rectification behavior in semi-stochastic polycrystalline graphene with graded grain-density distribution

arXiv (Cornell University), Jul 24, 2023

Thermal rectifiers are devices that have different thermal conductivities in opposing directions ... more Thermal rectifiers are devices that have different thermal conductivities in opposing directions of heat flow. The realization of practical thermal rectifiers relies significantly on a sound understanding of the underlying mechanisms of asymmetric heat transport, and two-dimensional materials offer a promising opportunity in this regard owing to their simplistic structures together with a vast possibility of tunable imperfections. However, the in-plane thermal rectification mechanisms in 2D materials like graphene having directional gradients of grain sizes have remained elusive. In fact, understanding the heat transport mechanisms in polycrystalline graphene, which are more practical to synthesize than large-scale singlecrystal graphene, could potentially allow a unique opportunity, in principle, to combine with other defects and designs for effective optimization of thermal rectification. In this work, we investigate the thermal rectification behavior in periodic atomistic models of polycrystalline graphene whose grain arrangements were generated semi-stochastically to have different gradient grain-density distributions along the in-plane heat flow direction. We employ the centroidal Voronoi tessellation technique to generate realistic grain boundary structures for graphene, and the non-equilibrium molecular dynamics simulations method is used to calculate the thermal conductivities and rectification values. Additionally, detailed phonon characteristics and propagating phonon spatial energy densities are analyzed based on the fluctuationdissipation theory to elucidate the competitive interplay between two underlying mechanisms, namely, (i) propagating phonon coupling and (ii) temperature-dependence of thermal conductivity that determines the degree of asymmetric heat flow in graded polycrystalline graphene.

Research paper thumbnail of Viscoelastic damping in crystalline composites: A molecular dynamics study

Composites Part B-engineering, May 1, 2016

Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jon... more Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jones (LJ) crystalline composites subject to an oscillatory shear deformation. The two crystals, namely a soft and a stiff phase, individually show highly elastic behavior and very small loss modulus. On the other hand, when the stiff phase is included within the soft matrix as a sphere, the composite exhibits significant viscous damping and a large phase shift between stress and strain. In fact, the maximum loss modulus in these model composites was found to be about 20 times greater than that given by the theoretical Hashin-Shtrikman upper bound. We attribute this behavior to the fact that in composites shear strain is highly inhomogeneous and mostly accommodated by the soft phase. This is corroborated by mode-dependent Grüneisen parameter analysis showing that in the low frequency regime, Grüneisen parameters, which measure degree of anharmonicity, are about twice greater for the composite than each individual homogenous crystal. Interestingly, the frequency at which the damping is greatest scales with the microstructural length scale of the composite, a feature we also observe for superlattice structures.

Research paper thumbnail of Generation of amorphous carbon models using liquid quench method: A reactive molecular dynamics study

Carbon, Mar 1, 2017

Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of ... more Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of amorphous carbon (a-C) at a wide range of densities (from 0.5 g/cc to 3.2 g/cc) via the "liquid-quench" method. A systematic study is undertaken to characterize the structural features of the resulting a-C models as a function of carbon density and liquid quench simulation conditions: quench rate, type of quench (linear or exponential), annealing time and size of simulation box. The structural features of the models are investigated in terms of pair correlation functions, bond-angles, pore-size distribution and carbon hybridization content. Further, the influence of quench conditions on hybridization/graphitization is investigated for different stages of the simulation. We observe that the structural features of generated a-carbon models agree well with similar models reported in literature. We find that in the low-density regime, size

Research paper thumbnail of Modeling high-temperature diffusion of gases in micro and mesoporous amorphous carbon

Journal of Chemical Physics, Aug 24, 2015

In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using e... more In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using equilibrium molecular dynamics simulations. Microporous and mesoporous carbon structures are computationally generated using liquid quench method and reactive force fields. Motivated by the need to understand high temperature diffusivity of light weight gases like H 2 , O 2 , H 2 O, and CO in amorphous carbon, we investigate the diffusion behavior as function of two important parameters: (a) the pore size and (b) the concentration of diffusing gases. The effect of pore size on diffusion is studied by employing multiple realizations of the amorphous carbon structures in microporous and mesoporous regimes, corresponding to densities of 1 g/cm 3 and 0.5 g/cm 3 , respectively. A detailed analysis of the effect of gas concentration on diffusion in the context of these two porosity regimes is presented. For the microporous structure, we observe that predominantly, a high diffusivity results when the structure is highly anisotropic and contains wide channels between the pores. On the other hand, when the structure is highly homogeneous, significant molecule-wall scattering leads to a nearly concentration-independent behavior of diffusion (reminiscent of Knudsen diffusion). The mesoporous regime is similar in behavior to the highly diffusive microporous carbon case in that diffusion at high concentration is governed by gas-gas collisions (reminiscent of Fickian diffusion), which transitions to a Knudsen-like diffusion at lower concentration.

Research paper thumbnail of Competing mechanisms govern the thermal rectification behavior in semi-stochastic polycrystalline graphene with graded grain-density distribution

Thermal rectifiers are devices that have different thermal conductivities in opposing directions ... more Thermal rectifiers are devices that have different thermal conductivities in opposing directions of heat flow. The realization of practical thermal rectifiers relies significantly on a sound understanding of the underlying mechanisms of asymmetric heat transport, and two-dimensional materials offer a promising opportunity in this regard owing to their simplistic structures together with a vast possibility of tunable imperfections. However, the in-plane thermal rectification mechanisms in 2D materials like graphene having directional gradients of grain sizes have remained elusive. In fact, understanding the heat transport mechanisms in polycrystalline graphene, which are more practical to synthesize than large-scale single-crystal graphene, could potentially allow a unique opportunity, in principle, to combine with other defects and designs for effective optimization of thermal rectification. In this work, we investigate the thermal rectification behavior in periodic atomistic models...

Research paper thumbnail of Does the doping strategy of ferrite nanoparticles create a correlation between reactivity and toxicity?

Environmental Science: Nano

The doping strategy of ferrite nanoparticles induced a correlation between their reactivity and t... more The doping strategy of ferrite nanoparticles induced a correlation between their reactivity and toxicity. The evidence showed the induction of biological responses as a factor of their dissolution and suspension properties of ferrite nanoparticles.

Research paper thumbnail of A Generative Approach to Materials Discovery, Design, and Optimization

Research paper thumbnail of Viscoelastic and Dynamic Properties of Well-Mixed and Phase-Separated Binary Polymer Blends: A Molecular Dynamics Simulation Study

Macromolecules, 2017

The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend... more The viscoelasticity and dynamic properties of a model dynamically asymmetric binary polymer blend are studied via molecular dynamics simulations. The model blend system is made up of two chain types having a large glass transition temperature (T g) difference and presents two blend morphologies: a well-mixed, homogeneous blend and a phase-separated blend. These two morphologies represent dynamically coupled and dynamically confined states. The well-mixed, homogeneous blend exhibited greater storage modulus and slower low-T g matrix chain dynamics compared to the phase-separated blend. The influence of various system parameters, such as high-T g chain length and (volume) concentration, and shear frequency on various static, dynamic, and viscoelastic properties is investigated to identify the source of the observed stiffening in the well-mixed, homogeneous blends.

Research paper thumbnail of Generation of amorphous carbon models using liquid quench method: A reactive molecular dynamics study

Carbon, 2017

Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of ... more Using molecular dynamics simulations with a reactive force field (ReaxFF), we generate models of amorphous carbon (a-C) at a wide range of densities (from 0.5 g/cc to 3.2 g/cc) via the "liquid-quench" method. A systematic study is undertaken to characterize the structural features of the resulting a-C models as a function of carbon density and liquid quench simulation conditions: quench rate, type of quench (linear or exponential), annealing time and size of simulation box. The structural features of the models are investigated in terms of pair correlation functions, bond-angles, pore-size distribution and carbon hybridization content. Further, the influence of quench conditions on hybridization/graphitization is investigated for different stages of the simulation. We observe that the structural features of generated a-carbon models agree well with similar models reported in literature. We find that in the low-density regime, size

Research paper thumbnail of Viscoelastic damping in crystalline composites: A molecular dynamics study

Composites Part B: Engineering, 2016

Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jon... more Molecular dynamics (MD) simulations were used to study viscoelastic behavior of model Lennard-Jones (LJ) crystalline composites subject to an oscillatory shear deformation. The two crystals, namely a soft and a stiff phase, individually show highly elastic behavior and very small loss modulus. On the other hand, when the stiff phase is included within the soft matrix as a sphere, the composite exhibits significant viscous damping and a large phase shift between stress and strain. In fact, the maximum loss modulus in these model composites was found to be about 20 times greater than that given by the theoretical Hashin-Shtrikman upper bound. We attribute this behavior to the fact that in composites shear strain is highly inhomogeneous and mostly accommodated by the soft phase. This is corroborated by mode-dependent Grüneisen parameter analysis showing that in the low frequency regime, Grüneisen parameters, which measure degree of anharmonicity, are about twice greater for the composite than each individual homogenous crystal. Interestingly, the frequency at which the damping is greatest scales with the microstructural length scale of the composite, a feature we also observe for superlattice structures.

Research paper thumbnail of Modeling high-temperature diffusion of gases in micro and mesoporous amorphous carbon

The Journal of chemical physics, Jan 28, 2015

In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using e... more In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using equilibrium molecular dynamics simulations. Microporous and mesoporous carbon structures are computationally generated using liquid quench method and reactive force fields. Motivated by the need to understand high temperature diffusivity of light weight gases like H2, O2, H2O, and CO in amorphous carbon, we investigate the diffusion behavior as function of two important parameters: (a) the pore size and (b) the concentration of diffusing gases. The effect of pore size on diffusion is studied by employing multiple realizations of the amorphous carbon structures in microporous and mesoporous regimes, corresponding to densities of 1 g/cm(3) and 0.5 g/cm(3), respectively. A detailed analysis of the effect of gas concentration on diffusion in the context of these two porosity regimes is presented. For the microporous structure, we observe that predominantly, a high diffusivity results when the...

Research paper thumbnail of Tensile and Viscoelastic Behavior in Nacre-Inspired Nanocomposites: A Coarse-Grained Molecular Dynamics Study

Nanomaterials

Organisms hold an extraordinarily evolutionary advantage in forming complex, hierarchical structu... more Organisms hold an extraordinarily evolutionary advantage in forming complex, hierarchical structures across different length scales that exhibit superior mechanical properties. Mimicking these structures for synthesizing high-performance materials has long held a fascination and has seen rapid growth in the recent past thanks to high-resolution microscopy, design, synthesis, and testing methodologies. Among the class of natural materials, nacre, found in mollusk shells, exhibits remarkably high mechanical strength and toughness. The highly organized “brick and mortar” structure at different length scales is a basis for excellent mechanical properties and the capability to dissipate energy and propagation in nacre. Here, we employ large-scale atomistic coarse-grained molecular dynamics simulations to study the mechanical and viscoelastic behavior of nacre-like microstructures. Uniaxial tension and oscillatory shear simulations were performed to gain insight into the role of complex s...