Wetting simulations of high-performance polymer resins on carbon surfaces as a function of temperature using molecular dynamics

Resin/reinforcement wetting is a key parameter in the manufacturing of carbon nanotube (CNT)-based composite materials. Determining the contact angle between combinations of liquid resin and reinforcement surfaces is a common method for quantifying wettability. As experimental measurement of contact angle can be difficult when screening multiple high-performance resins with CNT materials such as CNT bundles or yarns, computational approaches are necessary to fa-cilitate CNT composite material design. A molecular dynamics simulation method is developed to predict the contact angle of high-performance polymer resins on CNT surfaces dominated by aromatic carbon, aliphatic carbon, or a mixture thereof (amorphous carbon). Several resin systems are simulated and compared. The results indicate that the monomer chain length, chemical groups on the monomer, and simulation temperature have a significant impact on the predicted contact angle values on the CNT surface. Difunctional epoxy and cyanate ester resins show the overall highest levels of wettability, regardless of the aromatic/aliphatic nature of the CNT material surface. Tetra-functional epoxy demonstrates excellent wettability on aliphatic-dominated surfaces at elevated temperatures. Bismaleimide and benzoxazine resins show intermediate levels of wetting, while typ-ical molecular weights of polyether ether ketone demonstrate poor wetting on the CNT surfaces

MD modeling of epoxy-base nanocomposites reinforced with functionalized graphene nanoplatelets

The impact on the mechanical properties of aerospace epoxy materials reinforced with pristine Graphene Nanoplatelets (GNP), highly concentrated Graphene Oxide (GO), and Functionalized Graphene Oxide (FGO) has been investigated in this study. Molecular Dynamics (MD) using a reactive force field (ReaxFF) has been employed in predicting the effective mechanical properties of the interphase region of the three proposed nanocomposite materials at the nanoscale level. A systematic computational approach to simulate the reinforcing nanoplatelets and probe their influence on the mechanical properties of the epoxy matrix are included in this study. The nanoscale outcome indicates a significant degradation in the in-plane elastic Young’s (decreased by ~89%) and shear (decreased by ~72.5%) moduli of the nanocomposite when introducing large amounts of oxygen and functional groups to the robust sp2 structure of the GNP. However, the wrinkled morphology of GO and FGO improves the nanoplatelet-matrix interlocking mechanism which produces a significant improvement in the out-of-plane shear modulus (increased by ~95%). The influence of the nanoplatelet content and aspect ratio on the mechanical response of the nanocomposites has also been determined in this study. Generally, the predicted mechanical response of the bulk nanocomposite materials demonstrates an improvement with increasing nanoplatelet content and aspect ratio. The results show good agreement with experimental data available from the literature

A computational molecular dynamic study on epoxy-based network: thermo-mechanical properties

A computational molecular dynamics model for determining the thermomechanical properties of EPON 862 and DETDA systems was developed using OPLS all atoms force field. The approach for building heavily cross-linked epoxy-based network is defined and presented. The simulations allowed thermal properties such as glass transition temperature and coefficient of thermal expansion; as well as elastic properties of the materials to be estimated. The results exhibited a good agreement with both available experimental data and simulated results in literature

Computational modeling of hybrid carbon fiber/epoxy composites reinforced with functionalized and non-functionalized graphene nanoplatelets

The mechanical properties of aerospace carbon fiber/graphene nanoplatelet/epoxy hybrid composites reinforced with pristine graphene nanoplatelets (GNP), highly concentrated graphene oxide (GO), and Functionalized Graphene Oxide (FGO) are investigated in this study. By utilizing molecular dynamics data from the literature, the bulk-level mechanical properties of hybrid composites are predicted using micromechanics techniques for different graphene nanoplatelet types, nanoplatelet volume fractions, nanoplatelet aspect ratios, carbon fiber volume fractions, and laminate lay-ups (unidirectional, cross-ply, and angle-ply). For the unidirectional hybrid composites, the results indicate that the shear and transverse properties are significantly affected by the nanoplatelet type, loading and aspect ratio. For the cross-ply and angle ply hybrid laminates, the effect of the nanoplate’s parameters on the mechanical properties is minimal when using volume fractions and aspect ratios that are typically used experimentally. The results of this study can be used in the design of hybrid composites to tailor specific laminate properties by adjusting nanoplatelet parameters

Probing the Influence of Surface Chemical Functionalization on Graphene Nanoplatelets-Epoxy Interfacial Shear Strength Using Molecular Dynamics

In this work, a characterization study of the interfacial interaction between different types of graphene nanoplatelets and an epoxy matrix is computationally performed. To quantify the discrete mutual graphene–epoxy “interfacial interaction energy” (IIE) within the nanocomposite, molecular dynamics simulations with a reactive force field are performed on a localized model of the suggested nanocomposite. Pull-out molecular dynamics simulations are also performed to predict the interfacial shear strength between the two constituents. The results indicate a significant increase in interfacial adhesion of functionalized nanoplatelets with the hosting epoxy matrix relative to virgin graphene nanoplatelets. The obtained results also demonstrate a dramatic increase in the interfacial interaction energy (IIE) (up to 570.0%) of the functionalized graphene/epoxy nanocomposites relative to the unmodified graphene/epoxy nanocomposites. In the same context, the surface functionalization of graphene nanoplatelets with the polymer matrix leads to a significant increase in the interfacial shear strength (ISS) (up to 750 times). The reported findings in this paper are essential and critical to producing the next generation of lightweight and ultra-strong polymer-based nanocomposite structural materials

Comparing the mechanical response of di-, tri-, and tetra-functional resin Epoxies with reactive molecular dynamics

The influence of monomer functionality on the mechanical properties of epoxies is studied using molecular dynamics (MD) with the Reax Force Field (ReaxFF). From deformation simulations, the Young\u27s modulus, yield point, and Poisson\u27s ratio are calculated and analyzed. Comparison between the network structures of distinct epoxies is further advanced by the monomeric degree index (MDI). Experimental validation demonstrates the MD results correctly predict the relationship in Young\u27s moduli. Therefore, ReaxFF is confirmed to be a useful tool for studying the mechanical behavior of epoxies

Multiscale modeling of carbon fiber- graphene nanoplatelet-epoxy hybrid composites using a reactive force field

Numerous research efforts have been focused on developing lightweight epoxy-based composite materials that rival expensive metal alloys in aerospace structural components. Due to their high specific stiffness and strength, carbon fiber (CF)/graphene nanoplatelet (GNP)/epoxy hybrid composites are excellent candidates for this purpose. The objective of this study is to develop a multiscale modeling approach to predict the effective mechanical properties of a CF/GNP/epoxy composite material. The work-flow of this study involves molecular dynamics (MD) simulation with a reactive force field to predict the structure and behavior of the GNP/epoxy material at the molecular level and micromechanics to predict the mechanical properties of the CF/GNP/epoxy hybrid composite at the bulk level. The study provides evidence of an alignment behavior of phenyl rings in epoxy with the planar GNP surface at the interphase region. The results also indicate the validity of using a reactive force field as they compare well with experiment

Predicting thermal conductivity of graphene nanoplatelet/epoxy nanocomposite using non-equilibrium molecular dynamics

The thermal properties of Cycloaliphatic Epoxies (CE) and Anhydride Curing Agent (ACA) are predicted using Molecular Dynamics (MD) simulations with the Optimized Potential for Liquid Simulation (OPLS) force field. A modeling procedure has been developed to simulate the unique continuous crosslinking process of this material system, which has not been previously achieved. The predicted glass-transition temperature is in good agreement with experiment. The thermal conductivity is determined by using Non-Equilibrium MD (NEMD) techniques and is also close to the experimental value

Applying reactive molecular dynamics to predict and compare the mechanical response of di-, tri-, and tetra-functional resin epoxies

The influence of monomer functionality on the mechanical properties of epoxies is studied using Molecular Dynamics (MD) with the Reax Force Field (ReaxFF). From straining simulations, the Young’s modulus, yield point, and Poisson’s ratio are calculated and analyzed. The results demonstrate an increase in stiffness and yield strength with increasing resin functionality. Experimental comparisons show reasonable agreement, and therefore, this technique is confirmed to be a useful tool for understanding the structure-property relationships of epoxies