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Abstract A computational finite element analysis based on a structural molecular mechanics approach was conducted to predict effective coefficients of thermal expansion (CTE) of a novel three-dimensional carbon nanostructure, pillared graphene structure (PGS), which is constituted with several graphene sheets and single-walled carbon nanotubes. Four sets of representative unitcell models were developed atomistically having different geometric parameters of pillar length and inter-pillar distance in the PGS. Periodic boundary conditions were applied to periodic unitcell geometries to yield consistent results. Parametric study shows that both pillar length and inter-pillar distance significantly affect the effective in-plane and through-thickness CTEs. The PGS with smaller inter-pillar distance and larger pillar length yields higher in-plane CTEs, while that with larger inter-pillar distance and smaller pillar length yields higher through-thickness CTE. The calculation yields negative through-thickness CTE at low temperatures (T < 100 K) for all sets of PGSs, which is associated with the curvature at the junction. [ABSTRACT FROM AUTHOR]

Thermal energy transfer at the interconnects in carbon based nanoelectronic devices plays a crucial role towards their performance as well as their reliability. In this study, we investigate such thermal energy transfer across physically interacting multi-wall carbon nanotubes (MWCNTs) as a function of their diameter, length, number of walls, inter-layer chirality differences, and different angular orientation of the cross-contact. Using non-equilibrium molecular dynamics simulations for phonon energy transfer, we predict that MWCNTs' curvature and their number of walls emerge as two critical factors, with each of them determining the limiting value of the thermal conductance across MWCNT contacts in different diameter regimes. For thinner MWCNTs, the curvature determines the limiting value of the conductance and leads to an interesting non-monotonic character, while the number of walls dominates the contact conductance for large diameter MWCNTs. We discuss their respective origins and distinguish their governing regimes using several arguments –focusing of phonons, and confinement of the phonon focusing cone, large mean free path of graphite– and how they modulate radial thermal transport, leading to observed trends of thermal conductance across MWCNT contacts. [ABSTRACT FROM AUTHOR]

We have developed a computational scheme to predict stiffness and strength of carbon nanostructures under various loading modes. The prediction method is based on combined molecular mechanics and molecular dynamics simulations to approach a global energy minimum at a given loading level with a preset temperature tolerance of 10 −6 K. We have applied the present method to various carbon nanostructures including carbon nanotubes (CNTs), graphene, CNT with defects, a CNT-graphene junction and pillared graphene nanostructures. For all cases, we have identified the maximum stress and strain at failure of these carbon nanostructures as well as their critical failure modes, and discussed mechanisms that lead to their catastrophic failure. [ABSTRACT FROM AUTHOR]

Abstract: A computational finite element analysis based on a structural molecular mechanics approach was conducted to predict effective mechanical stiffness properties of a novel 3D carbon structure, pillared graphene structure (PGS), which is constituted with several graphene sheets and single-walled carbon nanotubes. Four sets of representative unitcell models were developed atomistically for predicting the mechanical properties of PGSs having different values of pillar length and inter-pillar distance. We introduced proper selections of the periodic geometry and boundary conditions which enabled our unitcell model to yield consistent results on the property prediction without any size or edge effects. The parametric study shows that the pillar length and inter-pillar distance significantly affect the effective in-plane and through-thickness properties. PGSs with shorter pillars in height yield higher planar Young’s and shear moduli, while those with smaller inter-pillar distance yield higher through-thickness moduli. Negative in-plane Poisson’s ratios are observed for all sets of PGSs and are associated with the curvature at the junction. [Copyright &y& Elsevier]

Abstract: In this article, we have investigated the anisotropic nature of thermal transport in molybdenum disulphide using molecular dynamics simulations. At first, a force field has been validated with respect to crystal structure and experimental vibrational spectra of MoS2. Thereafter, non-equilibrium MD simulations have been performed in two perpendicular directions (along as well as across the basal planes) to study thermal transport behavior. At room temperature, our results show an anisotropic factor of ∼4 in the values of thermal conductivity along two studied directions, which is in good agreement with recent experiments on MoS2 thin films. However, the predicted values of thermal conductivity are about an order of magnitude higher with respect to experiments. The reasoning behind these differences has been discussed in terms of layer disorder and the large number of grain boundary interfaces in experimental thin films, which consisted of nano-crystalline MoS2 grains with a predominant parallel or perpendicular basal plane orientation. Incorporation of phonon scattering via structure disorder and boundary interfaces were identified as further directions for the model refinement. [Copyright &y& Elsevier]

Abstract: In this article, thermal behavior of an epoxy based thermoset polymer has been discussed using atomistic molecular dynamics simulations. The simulations were performed on crosslinked network of EPON-862 and curing agent-W (DETDA) using consistent valence force field (CVFF). Thermal conductivity was calculated using both equilibrium as well as non-equilibrium molecular dynamics approaches and the results were found to be in good agreement with experimental findings. Different contributions of heat flux vector towards thermal conductivity and their possible coupling are discussed in terms of various convective and virial contributions. In addition, discussion of power spectra analysis of velocity autocorrelation function for crosslinked network shows a broad distribution of low frequency vibrational modes suggesting distribution of relaxation times. [Copyright &y& Elsevier]