REVIEW A review on the role of interface in mechanical, thermal, and electrical properties of polymer composites Marjan Alsadat Kashfipour 1 & Nitin Mehra 1 & Jiahua Zhu 1 # Springer International Publishing AG, part of Springer Nature 2018 Abstract Composite materials and especially polymer composites are widely used in daily life and different industries due to their vastly different properties and design flexibility. It is known that the properties of the composites are strongly related to the properties of its constituents. However, it has been reported in many studies, experimentally and by simulations, that the characteristics of the composites do not follow the rule of mixing. It means that in addition to properties of the constituents, there are other parameters affecting the final physicochemical properties of composites. The interfacial interactions between fillers and host is one of the factors which can strongly affect the properties of the composite. In this review, we summarized the type of interactions between the constituents, their improvement techniques, interaction measurement methods, and the effects of interfacial interactions on thermal, mechanical, and electrical properties of composites. Keywords Interface . Composites . Thermal conductivity . Mechanical strength . Electrical conductivity 1 Introduction Polymers are molecules made of long chains of repeated units known as monomers. Their intrinsic features of flexi- bility, light-weight and low production cost, allow them to have wide applications in our daily life such as food pack- aging, painting, and automobile industries, etc. Although the monomer structure and selection of polymerization methods allow good control on some of the polymer properties, cer- tain functions cannot be achieved by polymer itself. Therefore, polymers are compounded with other additives to achieve new properties. This final product is called com- posite [1]. Polymer nanocomposites (PNCs) are defined as the polymer matrixes reinforced with fillers with at least one dimension within 100 nm range. Nanofillers can be cate- gorized based on their dimensions, e.g. 0D particle, 1D tube/fiber, and 2D sheets [2]. The PNCs have attracted great attention due to their drastically enhanced properties [3–5]. For instance, thermally insulating polymers can be transformed into thermal conductors after reinforcing with carbon nanotubes (CNTs) [6–8]. Moreover, PNCs have demonstrated improved mechanical, gas barrier, solvent resistance, and flammability properties compared to the corresponding neat matrices [3, 4, 9]. The significant dif- ferences in properties of PNCs can be explained by the extremely large interface area of nanofiller. The interfacial area of nanofillers is orders of magnitude higher than tra- ditional macro- or micron-sized additives [ 10 , 11 ]. Therefore, the dispersion quality of nanofillers in polymer matrix becomes critically important. The techniques of incorporating nanofillers, dispersion control, and their im- pacts on the physicochemical properties of PNCs have been reviewed broadly [12–15]. Although the type and chemistry of the nanofillers are im- portant for the prediction of their composite properties, the experimental and modeling results have not completely been in compliance with the predicted behavior. Therefore, there should have been other parameters which have either underestimated or not been considered in the prediction of composite behavior. In this regard, the interfacial interaction between polymer matrix and nanofiller became one of the parameters which have raised attention [16–19]. The presence of nanofillers in the matrix and their interfacial interaction can affect the mobility of polymer chains [20]. At high filler * Jiahua Zhu jzhu1@uakron.edu 1 Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, USA https://doi.org/10.1007/s42114-018-0022-9 Advanced Composites and Hybrid Materials (2018) 1: – 415 439 Received: 15 November 2017 /Accepted: 22 January 2018 /Published online: 26 February 2018