Due to the quick growth in the utilization of commercial, industrial and military applications, EMI has become a serious concern in modern society. Light-weight EMI shielding is needed to protect the environment and workplace from EMI due to unwanted electromagnetic waves, especially for the building containing power transformers and other electronic facilities, which will radiate electromagnetic wave to the environment. Electrically conductive polymer composites containing carbon-based fillers have been extensively investigated recently for EMI shielding applications [1–3]. Compared to conventional metal-based EMI shielding materials, they are light weight, resistant to corrosion and flexible .
Recently, multiwalled carbon nanotubes (MWCNTs)/polymer conductive composites have received extensive considerable attentions in both fundamental and applied research fields. Previous studies on the MWCNTs and their diversified applications show that MWCNTs possess excellent electrical, mechanical properties and unique one-dimensional structure [5–10], which make them an ideal option to create overlapping conductive network for high-performance EMI shielding at low loadings [11–13]. Many MWCNTs/polymer composites in typical solutions or melt-based systems have been studied with various polymer matrix, including epoxy , shape memory polymer , poly(methyl methacrylate) (PMMA) , polyurethane , for various applications such as effective and light-weight EMI shielding, microwave absorption, high charge storage capacitors. However, the polymer composite materials with MWCNTs in water-based systems have been largely unexplored and more environmentally friendly, for there is no or negligible content of volatile organic compounds. It has been reported that the defective arc-made MWCNTs have a high dielectric constants , and the theory prediction shows that the lattice defects can create localized states near the Fermi level , which can give rise to large microwave absorption. The defects on the MWCNTs can be introduced by a special purification process [19–21].
Styrene acrylic emulsion is widely used in the field of the architectural paints for its prominent properties such as high resistance to UV light, oxygen, water, various types of solvents and excellent durability . However, styrene acrylic emulsion-based polymer alone has a low conductivity and provides no shielding property. It seems reasonable to prepare styrene acrylic emulsion-based composites for building shielding materials by incorporating WMCNTs with all the excellent properties mentioned earlier.
In this study, we prepared a styrene acrylic emulsion-based composite with well-dispersed MWCNTs for building EMI shielding applications. The structural characteristics of the MWCNTs and composites were investigated through field-emission scanning microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy experiments. The DC conductivity (σ
dc), complex permittivity and EMI SE of the composites in 8.2–12.4 GHz were reported. The AC conductivity (σ
ac) of the composites, calculated from imaginary permittivity, was used to estimate the SE of the composites in the far field.