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Top1. Introduction
In recent years, remarkable attention towards use of nanofillers as multi-functional reinforcement of polymer matrices has been growing both in academic researches and in industry. Thus, conventional materials are replaced more by nanomaterials (Bhattacharya, Kamal, and Gupta, 2008; Njuguna, Pielichowski, & Fan, 2012; Pfaendner, 2010). From mechanical point of view, due to enormous surface area to volume as well as high aspect ratio (length to diameter) of some nanofillers such as carbon nanotube (CNT) and carbon fiber (CNF), nanocomposites containing such materials show different properties from typical composites (Ayatollahi, Shadlou, Shokrieh, & Chitsazzadeh, 2011; Shokrieh, Daneshvar, Akbari, & Chitsazzadeh, 2013). Besides physical and chemical properties, the mechanical properties of the final composite are significantly affected by the strong interactions created at the matrix-filler interface (Pan et al., 2013; Rahmat & Hubert, 2011; Cui, Canet, Derre, Couzi, & Delhaes, 2003). However, there are some challenges to create high performance carbon nanotubes composites. Due to the sp2 bonds and the high intermolecular attraction between the bundles caused by Vander Waals forces, the dispersion of these fillers in the matrix and organic solvents is usually an issue. CNTs tend to agglomerate and are difficult to disperse in the host polymer. Therefore, the key challenge in manufacturing process of nanocomposite materials is to obtain a homogenous dispersion of nanotubes in the matrix.
Several methods have been introduced and then developed to prepare uniformly dispersed nanotube reinforced composites. These include the use of surfactants (Gong, Liu, Baskaran, Voise, & Young, 2000), high shear mixing (Gojny, Wichmann, Köpke, Fiedler, & Schulte, 2004; Qian, Dickey, Andrews, & Rantell, 2000), sonication (Qian, Dickey, Andrews, & Rantell, 2000; Chitsazzadeh, Shahverdi, and Shokrieh, 2011) and chemical functionalization of the outside wall of the tubes (Dyke & Tour, 2004). Rheology, the study of the flow behavior of a material under various conditions, is concerned with establishing predictions for mechanical behavior (on the continuum mechanical scale) based on the micro- or nanostructure of the materials (Prentice, 1995). The study of rheological response of CNT/polymer nanocomposites have both practical importance related to composite processing and scientific importance as a probe of the composite dynamics and microstructure (Moniruzzaman & Winey, 2006). Also, measuring viscosity and rheological properties have proven to be able to express the dispersion state of CNTs (Huang, Y. Y., and E. M. Terentjev, 2008).
Dynamic mechanical thermal analysis (DMTA) is also another effective method to investigate the dispersion state of CNT in the polymer matrix as well as viscoelastic properties of fabricated nanocomposite. Viscoelastic properties of a polymer are significant because physical functions of polymer depend highly on them. In order to study the viscoelastic behavior, modeling can be used too. Through modeling, one can compare the effects of fillers and additive on the viscoelastic properties of a polymer.