Abstract:

Adding high thermal conductivity materials to salt hydrate phase change materials is an effective approach to promote the thermal performance of salt hydrates. However, significant thermal resistance occurs at the interfaces when different materials are combined. In this study, molecular dynamics simulations were employed to calculate the temperature distribution, thermal conductivity, radial distribution function (RDF) and phonon density of states (PDOS) in solid and liquid states, respectively, to investigate the atomic distribution, heat transport, and phonon transport at the interface of sodium acetate trihydrate (SAT) and graphene composite materials to explore the mechanism behind interface thermal resistance from a microscopic perspective. Temperature calculation results indicated that in both solid and liquid states, significant temperature gradients existed at the graphene/SAT interface with a thermal resistance at the interface approximately 4.5 times greater than that of other regions. RDF calculations revealed that in the solid state of graphene/SAT composite materials, the distance between graphene surface atoms increased, forming a vacuum layer, while in the liquid state, the atomic aggregation occurred on the graphene surface. PDOS calculations demonstrated that the addition of graphene disrupted the low-frequency phonon distribution in the vicinity of the interface, leading to increased phonon scattering, and then reduced thermal efficiency. This disruption diminished with increasing distance from graphene and essentially disappeared at 3nm.

Key words: sodium acetate trihydrate, graphene, molecular dynamic, interface thermal resistance, phonon densities of states

摘要：

利用高导热材料复合水合盐是提高水合盐相变材料导热性能的有效途径之一。但不同材料复合时会在界面处产生较大热阻。本研究采用分子动力学方法，分别计算了三水醋酸钠（SAT）/石墨烯复合相变材料在固态、液态时的温度分布、热导率、径向分布函数（RDF）、声子态密度（PDOS），以研究两种材料界面处的原子分布、热输运和声子输运，从微观角度探究界面热阻产生的机理。温度计算结果表明，在固态与液态时，SAT/石墨烯界面处都存在较大的温度梯度，交界处的热阻均为其他区域的4.5倍左右。RDF计算结果表明，材料在固态时，石墨烯表面原子之间距离增大，形成真空层；液态时，石墨烯表面反而会出现原子聚集的现象。PDOS计算结果表明，石墨烯的加入会导致界面附近区域的低频声子分布紊乱，从而增加声子散射，降低导热效率；这种紊乱会随着与石墨烯的距离增大而减弱，从3nm处基本消失。

关键词: 三水醋酸钠, 石墨烯, 分子动力学, 界面热阻, 声子态密度