石墨烯取向影响石墨烯/硝酸盐复合材料传热性能的分子动力学模拟

吴晨光; 李蓓

doi:10.13801/j.cnki.fhclxb.20210616.006

石墨烯取向影响石墨烯/硝酸盐复合材料传热性能的分子动力学模拟

doi: 10.13801/j.cnki.fhclxb.20210616.006

吴晨光^1,,
李蓓^{1, 2, ,}

1.
武汉理工大学　材料科学与工程学院材料基因工程研究中心，武汉 430070
2.
华中科技大学　材料成形与模具技术国家重点实验室，武汉 430070

基金项目: 华中科技大学材料成形与模具技术国家重点实验室开放课题研究基金(P2021-009)

详细信息

通讯作者:
李蓓，博士，副教授，博士生导师，研究方向为高分子、金属及纳米复合材料计算模拟　 E-mail：libei@whut.edu.cn

中图分类号: TB33
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出版历程
- 收稿日期: 2021-04-23
- 修回日期: 2021-05-30
- 录用日期: 2021-06-09
- 网络出版日期: 2021-06-16
- 刊出日期: 2022-03-23

Effect of graphene orientation on heat transfer properties of graphene/nitrates composites by molecular dynamics simulation

WU Chenguang^1
,,
LI Bei^{1, 2
, ,}

1.
Research Center for Materials Genome Engineering, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China
2.
State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430070, China

摘要

摘要: 采用非平衡分子动力学(NEMD)方法，以二元硝酸盐Solar salt(NaNO₃和KNO₃质量比为6∶4) 为基体，石墨烯为填料，研究了石墨烯取向对石墨烯/硝酸盐复合材料界面热导的影响。研究发现，随着石墨烯平面与热流方向夹角的减小，体系热流密度升高、温差下降，界面热导从46.36 MW·m⁻²·K⁻¹提升至80.03 MW·m⁻²·K⁻¹。对复合材料中的原子振动态密度和微观结构进行表征，结果发现，随着石墨烯与热流夹角减小，界面处的热流从跨石墨烯平面运输转变为沿石墨烯平面的高效率运输，且加入石墨烯后硝酸盐会形成密度较大的致密层结构。同时，采用有效介质理论拟合了微观尺寸的石墨烯/硝酸盐复合材料热导率，结果表明，石墨烯平行于热流方向时复合材料热导率最高，且增加石墨烯体积分数及长度均有助于复合材料热导率的增强。
- 分子动力学 /
- 界面热导 /
- 石墨烯 /
- 振动态密度 /
- 有效介质理论
Abstract: The effects of the graphene orientation on interfacial thermal conductivity of graphene/nitrate compo-sites with binary nitrate Solar salt(NaNO₃/KNO₃ mass ratio of 6∶4) as substrate and graphene as filler was investi-gated by non-equilibrium molecular dynamics (NEMD) method. It is shown that the interfacial thermal conductance can be considerably enhanced from 46.36 MW·m⁻²·K⁻¹ to 80.03 MW·m⁻²·K⁻¹ as the angle θ between the graphene surface and the heat flux direction (i.e., z direction) decreases from 90° to 0°. As the angle θ decreases, the effective projection of the graphene plane in the direction of heat flow is enhanced, and more heat will be transported along the graphene plane. The results of the vibrational density of state (DOS) clearly signify that heat flow at the interface changes from transport across the graphene plane to efficient transport along the graphene plane with the decrease of angle between graphene and heat flow. Moreover, the nitrates form a similar dense layer around the graphene for all different orientation angles, which would also promote the enhancement of the thermal conductance. Finally, the thermal conductivity of the graphene/nitrates composites with different orientations at the microscale is predicted by the effective medium theory. It is found that the thermal conductivity of the composite decreases with the orientation angle, but increases with the volume fraction and the length of the graphene.
- molecular dynamics /
- interfacial thermal conductance /
- graphene /
- vibrational density of states /
- effective medium theory

HTML全文

图 1 石墨烯、硝酸盐 (a)、石墨烯/硝酸盐复合材料 (b) 初始模型(θ=30°)

Figure 1. Initial models of graphene and nitrates (a) and graphene/nitrates composites (b) (θ=30°)

θ— Angle between the graphene plane and the heat flow direction (z direction); ΔT—Temperature difference between the two sides of the calculation area

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图 2 石墨烯/硝酸盐复合材料热流密度J

Figure 2. Heat flux J of graphene/nitrates composites

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图 3 石墨烯/硝酸盐复合材料体系热流方向上的温度分布

Figure 3. Temperature distribution of the graphene/nitrates composites in the direction of heat flow

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图 4 石墨烯在平面内和平面外的振动态密度 (a)、纯硝酸盐和石墨烯/硝酸盐复合材料沿热流方向(z方向)的振动态密度 (b)

Figure 4. In-plane and out-plane vibrational density of state of graphene (a), vibrational density of state of pure nitrates and graphene/nitrates composites along the heat flow direction (z direction) (b)

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图 5 石墨烯/硝酸盐复合材料密度分布(θ=0°)

Figure 5. Density distribution of graphene/nitrates composites (θ=0°)

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图 6 石墨烯/硝酸盐复合材料与纯硝酸盐中的N−N原子对分布函数图

Figure 6. N-N atom pair distribution function in graphene/nitrates composites and pure nitrates

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图 7 石墨烯/硝酸盐复合材料热导率增强系数有效介质理论模型结果与实验数据^[5]的对比

Figure 7. Comparison between the thermal conductivity of graphene/nitrates composites enhancement coefficient obtained from the effective medium theory model and the experimental data^[5]

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图 8 石墨烯/硝酸盐复合材料热导率随填料体积分数f的变化(石墨烯长度L=1.5 μm) (a) 及随填石墨烯长度L的变化(填料体积分数f=0.5vol%) (b)

Figure 8. Thermal conductivity of graphene/nitrates composites as a function of the volume fraction f with the graphene length L=1.5 μm (a) and as a function of the graphene length L with the volume fraction f=0.5vol% (b)

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表 1 石墨烯/硝酸盐复合材料势函数参数

Table 1. Potential parameters of graphene/nitrates composites

Atom	ε/meV	σ/nm	q/e
N	4.018	0.3431	0.95
O	3.469	0.3285	−0.65
K	4.336	0.3188	1
Na	6.637	0.2407	1
C	2.968	0.3407	0
Atoms
N−O	K_b=22.766 eV·nm⁻²	r₀=0.1268nm
O−N−O	K_θ=4.553 eV·rad⁻²	θ₀=120°
N−O−O−O	K_ψ=2.602 eV·rad⁻²	ψ₀=0°
Notes: ε—Unit of energy indicating the strength of the interaction between atoms; σ—Atomic spacing when the i atom interacts with the j atom is 0; q—Atomic charge; Harmonic parameters consist of bonds computed as V_b=K_b(r−r₀)², angles computed as V_θ=K_θ(θ−θ₀)², and an improper function of the form V_ψ=K_ψ(ψ−ψ₀)² to keep the nitrates species planar, where r₀, θ₀, ψ₀are the equilibrium parameters of the bond, and K_b, K_θ, K_ψ are the prefactors.

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表 2 石墨烯−硝酸盐复合材料界面热导G

Table 2. Thermal conductance G of graphene/nitrates composites

θ/(°)	90	75	60	45	30	15	0
J/(10⁹W·m⁻²)	2.16	2.49	2.65	2.63	2.74	2.85	2.91
ΔT/K	46.59	44.87	45.64	41.10	39.23	37.26	36.36
G/(MW·m⁻²·K⁻¹)	46.36	55.49	58.06	63.99	69.84	76.48	80.03

下载: 导出CSV

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