## 1 Introduction  
Epoxy resin (EP) is a kind of thermosetting material with excellent performances including electrical insulation, mechanical properties, and chemical stability, which have drawn wide application in power and industrial equipment [1; 2]. However, with the rapid development of power and industrial fields, epoxy materials equipment with superior performances is required. One common approach is to add nanomaterials such as carbon nanotubes (CNT), graphene, oxides, nitrides, and their mixture into various polymers, which not only retains the original excellent performance of pristine polymer, but also greatly enhances electrical, mechanical, and thermal properties [3; 4; 5; 6; 7; 8; 9; 10]. Especially, boron nitride nanosheet (BNNS) as nanofiller for epoxy composites has higher bandgap and better insulating performance when compared with graphene oxide (GO)/EP or graphene (GNP)/EP composites [11; 12; 13; 14; 15; 16; 17]. Since the physicochemical properties of nanomaterials and polymers are distinctly different, a clear interface is formed between them which plays a significant role in the macroproperties of nanocomposites [18; 19; 20]. Consequently, the knowledge and understanding of the interface characteristics are critical for design and manufacturing of novel polymer nanocomposites. Some experiments have been performed to explore the interfacial interaction of nanocomposites [21; 22; 23; 24]. The interfacial properties of nanocomposites such as the chain movement, density, and compatibility can be characterized by Raman spectroscopy, atomic force microscopy, and in situ transmission electron microscopy, which showed that the interface feature has a dominant effect on the properties of composites [25; 26; 27; 28]. The effect of interface characteristics on mechanical and physical properties of CNTs nanocomposites are investigated by measuring its surface microstructures, energy-dispersive spectroscopy, and fracture toughness, which pointed out that improving interfacial properties was a green and promising approach toward preparing high-performance composites [29; 30; 31]. [PERSON] and [PERSON] employed a modified Kelvin probe force microscopy method to detect the local polarization property at the matrix/particle interface in ferroelectric nanocomposites, and the results illuminated that the abnormal performance of ferroelectric nanocomposites stems from the interfacial region [32]. To explain these experimental results, several interface theories and models have been proposed to describe the interfacial interaction in nanocomposites [33]. [PERSON] [34] and [PERSON] [35] considered that the interfacial region could be split into two layers: a tightly bound layer (which does not contribute to the glass transition), and a loosely bound layer (which may exhibit its own glass transition unique from the rest of the polymer), which also indicated that the interfacial interactions can restrict chain mobility of this region. A more comprehensive multicore interfacial model composed of a bonded layer, a bound layer, and a loose layer is proposed by [PERSON], and the model has been successfully used to explain the mechanism of the decrease of dielectric constant, the inhibition of space charge, and the improvement of corona resistance from interfacial effects [36; 37]. These experiments and models were mainly used to determine the macro chemical-physical structure of the interface as well as its electrical properties. However, the interfacial characteristic of nanocomposites is not fully understood yet, and most of the interfacial models are assumed based on experimental results [38]. The development of molecular simulation technology provides a powerful tool to directly analyze the interface properties in nanocomposite from a microscopic perspective [39; 40].