Molecular dynamics simulation of thermal conductivity of diamond/epoxy resin composites
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Acta Physica Sinica |
| Authors | Xiucheng Liu, Zhi Yang, Hao Guo, Ying Chen, Xianglong Luo |
| Institutions | Guangdong University of Technology, Technical Institute of Physics and Chemistry |
| Citations | 5 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study uses Non-Equilibrium Molecular Dynamics (NEMD) to optimize nanodiamond/epoxy resin composites for high-performance Thermal Interface Materials (TIMs), addressing critical heat dissipation challenges in 5G and microelectronic devices.
- Core Value Proposition: Provides a design strategy for maximizing the thermal conductivity (TC) of epoxy-based TIMs by controlling nanodiamond filler morphology.
- Optimal Filling Strategy: Single-particle filling (using one large nanodiamond) is significantly more effective than multi-particle filling (using many small nanodiamonds) at the same mass fraction.
- Maximum TC Achievement: The composite TC reached 0.592 W·m-1·K-1 using 2 nm nanodiamonds (26.15% mass fraction), a 2.52x increase over pure cross-linked epoxy.
- Cross-linking Impact: Increasing the epoxy cross-linking rate from 0% to 90% significantly improved the intrinsic TC of the polymer matrix by 77% (up to 0.23 W·m-1·K-1).
- Mechanism of Enhancement: Larger particles enhance TC primarily by reducing the Fractional Free Volume (FFV) of the polymer matrix, which facilitates phonon transport.
- Mechanism of Limitation: Multi-particle filling increases the total specific surface area, leading to greater interfacial thermal resistance (Kapitza resistance), which severely limits overall TC improvement.
Technical Specifications
Section titled “Technical Specifications”Data extracted from the Molecular Dynamics simulations and material properties.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Pure Epoxy TC (Simulated, 90% cross-linked) | 0.23 | W·m-1·K-1 | Baseline TC of the polymer matrix. |
| Maximum Composite TC Achieved | 0.592 | W·m-1·K-1 | Achieved with 2 nm nanodiamonds (26.15% mass fraction). |
| TC Enhancement Ratio (Max) | 2.52x | Ratio | Relative increase over pure cross-linked epoxy. |
| Optimal Nanodiamond Size (Single-particle) | 2.0 | nm | Yields highest TC due to maximum FFV reduction. |
| Nanodiamond Intrinsic TC | 2000 | W·m-1·K-1 | High intrinsic conductivity of the filler material. |
| Optimal Epoxy Cross-linking Rate | 90.00 | % | Target rate for composite matrix preparation. |
| Cross-linking Temperature | 600 | K | Temperature used during the cross-linking reaction simulation. |
| Simulation Temperature (NEMD) | 300 | K | Average temperature maintained during heat flux calculation. |
| Simulation Time Step | 0.25 | fs | Time step used for NEMD thermal calculation. |
| Maximum Interfacial Thermal Resistance Factor | 3.71 | % | Fractional Free Volume (FFV) for 10 particles (30.38% mass fraction), indicating poor thermal performance. |
Key Methodologies
Section titled “Key Methodologies”The thermal conductivity was determined using Non-Equilibrium Molecular Dynamics (NEMD) implemented in LAMMPS, following a detailed simulation protocol:
- Monomer Selection: Bisphenol F diglycidyl ether (DGEBF) and diethyl toluene diamine (DETDA) were used as the epoxy monomer and cross-linker, respectively, mixed at a 2:1 molar ratio.
- Filler Preparation: Nanodiamond particles (1.0 nm to 2.0 nm radius) were constructed and their surfaces were hydrogen-terminated to ensure electrical neutrality and stability within the polymer matrix.
- Cross-linking Simulation: The amorphous DGEBF/DETDA model was cross-linked at 600 K, targeting a 90% cross-linking rate, using a maximum reaction cutoff distance of 10 Angstrom.
- Force Field Assignment:
- Epoxy: PCFF (Polymer Consistent Force Field) was used for internal polymer interactions.
- Diamond: Tersoff potential was used for carbon-carbon interactions within the diamond lattice.
- Interface: Lennard-Jones 12-6 potential, combined with Lorentz-Berthelot mixing rules, described the non-bonded interactions between the epoxy matrix and the nanodiamond filler.
- Equilibration: The composite models underwent sequential relaxation steps (Smart Minimizer, NVT, NPT at 300 K) to achieve stable density (approx. 1.1 g/cm³) and minimize internal stress before thermal testing.
- NEMD Calculation: Thermal conductivity was calculated using the local heat bath method (Langevin thermostat). A temperature gradient was established by setting a hot region (330 K) and a cold region (270 K) across the simulation box (divided into 20 bins).
- Data Collection: Heat flux and temperature profiles were sampled over 2500 ps of steady-state simulation, and TC was calculated using Fourier’s law.
Commercial Applications
Section titled “Commercial Applications”The findings directly support the design and manufacturing of high-performance thermal management solutions for demanding electronic systems.
- High-Density Microelectronic Cooling: Developing advanced TIMs (thermal pastes, gap pads) for high-power chips (CPUs, GPUs, FPGAs) where heat fluxes are continuously increasing due to higher integration.
- 5G/6G Infrastructure: Thermal management of high-frequency and high-power radio frequency (RF) components in base stations and communication modules.
- Power Electronics Packaging: Encapsulation and bonding materials for power modules (e.g., in electric vehicles or industrial drives) requiring high thermal stability and electrical insulation.
- Nanocomposite Manufacturing: Guiding the synthesis of high-TC polymer composites by emphasizing the use of larger filler particles over a higher number of smaller particles to minimize detrimental Kapitza resistance.
- Aerospace and Defense Electronics: Applications requiring lightweight, high-reliability thermal materials that maintain performance under extreme operating conditions.
View Original Abstract
Improving the thermal conductivity (TC) of epoxy resin thermal interface material is of great significance in tackling the heat dissipation problem of high heat flux in microelectronic chips such as 5G. Using non-equilibrium molecular dynamics (MD) method, the effects of two different filling styles of nano-diamond fillers on the TC of EP based composites are investigated. The results show that the TC of the composite increases with the diamond size when single-particle filling is used, and that a larger diamond size leads to a more significant reduction of the free volume fraction and thus an improvement of the TC. In the multi-particle packing, the composite TC first increases and then decreases with increasing particle number. Increasing the number of particles reduces the free volume fraction, but also results in a larger specific surface area and interfacial thermal resistance, which has a more significant weakening effect on the TC. Moreover, within the same mass fraction of nano-diamond filler, increasing the filler size has a more significant TC improvement on the composite than increasing the number of particles. This study is instructive for the design and preparation of high thermal conductivity nanodiamond/epoxy resin composites.