vdW Interaction Force Research Articles

Molecular Dynamics Simulations of DGEBA/OSC Epoxy Composites for Improving Heat-Resistance and Elastic Modulus

Thermal and mechanical properties of DGEBA/OSC epoxy composite polymers composed of both bisphenol A diglygde ether (DGEBA) and alicyclic epoxy resin (OSC) as co-polymerization monomers and 3,3-diaminodiphenyl sulfone (DDS) as curing agent are evaluated and investigated by molecular dynamics (MD) simulations, in which NPT ensembles and annealing cycles in a wide temperature range are utilized for modeling the thermodynamic equilibrium systems and heating processes. Glass transition and thermal-decomposition temperatures are calculated by linear fitting on the temperature dependence of elastic modulus, cohesive energy, fractional free-volume (FFV). It is verified that the two DGEBA/OSC epoxy composite can effectively improve the thermal and mechanical performances of epoxy polymer, in which DGEBA/OSC(1:1) epoxy composite are most significant of promoting mechanical stiffness and render a elevated glass transition temperature by 28 K and thermal-decomposition temperatures by 91 K, the two DGEBA/OSC epoxy composite are capable of efficiently reduce fractional free volume by 4.4% and 8.6% for DGEBA/OSC(3:1) and DGEBA/OSC(1:1) epoxy composite respectively, which is in consistent with the lower rotation amplitudes of crosslinking bonds for DGEBA/OSC composite EP polymers that vdW interaction forces between molecular-chains can be promoted by OSC co-polymeric blocks to inhibit thermal motions of EP molecular-chains.

Thermal Buckling Analysis of Circular Bilayer Graphene Sheets Resting on an Elastic Matrix Based on Nonlocal Continuum Mechanics

In this article, the thermal buckling behavior of orthotropic circular bilayer graphene sheets embedded in the Winkler–Pasternak elastic medium is scrutinized. Using the nonlocal elasticity theory, the bilayer graphene sheets are modeled as a nonlocal double–layered plate that contains small scale effects and van der Waals (vdW) interaction forces. The vdW interaction forces between the layers are simulated as a set of linear springs using the Lennard–Jones potential model. Using the principle of virtual work, the set of equilibrium equations are obtained based on the first-order shear deformation theory (FSDT) and nonlocal differential constitutive relation of Eringen. Differential quadrature method (DQM) is employed to solve the governing equations for simply-supported and clamped boundary conditions. Finally, the effects of the small scale parameter, vdW forces, aspect ratio, elastic foundation, and boundary conditions are considered in detail.

SsDNA TRANSLOCATION WITH CARBOXYL-MODIFIED TRANSMEMBRANE SINGLE-WALLED CARBON NANOTUBE

Functionalized transmembrane carbon nanotube (CNT) interactions are of significant importance in CNT-based drug delivery systems and biomedical devices. In this work, an all-atom molecular dynamics simulation is applied to study the encapsulation of a short single-stranded DNA (ssDNA) oligonucleotide in functionalized carbon nanotube (f-CNT) channels. We show that while the van der Waals (vdW) interaction between the ssDNA and the f-CNT induces a spontaneous encapsulation of the molecule within the nanotube channel, the vdW interaction between the ssDNA and biomembrane counteract the encapsulation. However, the vdW attraction due to the f-CNT is stronger than that from the membrane lipid bilayer, leading to the final encapsulation. In particular, we obtain the vdW interaction force between the ssDNA, biomembrane and the f-CNT analytically through a general mathematical model. This interaction force is found to play a dominate role in the adsorption process. The analytically obtained vdW force and potential fields show good correspondence with the adsorption conditions and the adsorption behavior of the ssDNA obtained numerically via the all-atom molecular dynamics simulation.

Torsional elastic instability of double-walled carbon nanotubes

In this paper, a theoretical analysis of the torsional buckling instability of double-walled carbon nanotubes (DWCNTs) and the DWCNTs embedded in an elastic medium is presented based on the continuum elastic shell model and Winkler spring model. Using the proposed theoretical approach, the influences of the aspect ratio, the buckling modes and the surrounding medium on the torsional stability are examined in detail. The simulation results show that the torsional instability of DWCNTs can occur in different buckling modes according to the aspect ratio. The van der Waals (vdW) interaction force between nanotubes reinforces the stiffness of nanoshells. Thus, the DWCNTs possess higher buckling stability than the SWCNTs without considering vdW interaction force.