Effects of sonochemical modification of carbon nanotubes on electrical and electromagnetic shielding properties of epoxy composites Rumiana Kotsilkova a , Evgeni Ivanov a,⇑ , Dmitry Bychanok b , Alesya Paddubskaya b , Marina Demidenko b , Jan Macutkevic d , Sergey Maksimenko b,c , Polina Kuzhir b,c a OLEM, Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, Bulgaria b Research Institute for Nuclear Problems, Belarusian State University, Minsk, Belarus c National Research Tomsk State University, Tomsk, Russia d Vilnius University, Vilnius, Lithuania article info Article history: Received 14 September 2014 Received in revised form 2 November 2014 Accepted 9 November 2014 Available online 13 November 2014 Keywords: A. Carbon nanotubes A. Hybrid composites Electromagnetic shielding B. Electrical properties D. Rheology abstract Electrical and electromagnetic interference shielding properties of epoxy/multi-walled carbon nanotube (MWCNTs) composites are studied for low nanotube contents from 0.03 to 0.3 wt.% and different process- ing conditions. In situ chemical modification of carbon nanotube surfaces was achieved by ultrasonic irra- diation of carbon nanotubes either in polyethylene polyamine or in liquid epoxy resin, resulting in amine- grafted or epoxy-grafted composites, respectively. Raman, TGA, and SEM analyses indicate a successful grafting of polymer chains to the nanotube surfaces. The amine-grafted MWCNT/epoxy composites show the presence of a thick polymer layer that has formed an extra phase on the carbon nanotube walls, which affects significantly the electrical conductivity and radio frequency response properties. Hence, the amine-grafted composites demonstrate a slightly higher percolation threshold (p c = 0.08 wt.%) and, at the same time, a lower absolute values of dc-conductivity as compared to that of the epoxy-grafted composites, with p c = 0.05 wt.%. In the radio frequency range, almost 3 orders of magnitude rise of the values of ac-conductivity was observed for small contents of the amine-grafted MWCNTs in epoxy. The epoxy-grafted composites could be proposed for producing effective antistatic and electrostatic dissipa- tion coatings. Around and above the percolation threshold, the amine-grafting is critical in the radio fre- quency range for producing coatings with large dielectric losses. The absolute values of microwave attenuation were found to be independent of the surface modification procedure, but strongly dependent on the concentration of MWCNTs and the thickness of the composite layer. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The use of carbon nanotubes (CNTs) as a filler in epoxy resin has attracted great attention due to the possibility to improve the com- posite properties for applications ranging from microelectronics to aerospace. The dispersion states of carbon nanotubes, the amount and the aspect ratio determine how easily CNTs can interact with each other to build an interconnecting network of percolation that can transfer phonons and electrons to enhance the properties of the nanocomposite [1–3]. As seen from the reviewed literature [4–8] and our previous studies [9–10], chemical functionalization of nanotube surfaces improved the compatibility of CNTs in epoxy resin and has a positive influence on rheological, electrical, ther- mal, mechanical, optical and other properties of polymer compos- ites with MWCNTs. Guadagno et al. [8] found that chemical functionalization of MWCNTs leads to the formation of an interface with stronger interaction; this causes a significant decrease in the electrical conductivity of the composite with respect to the untreated MWCNTs which is explained in terms of tunnelling resistance between interacting nanotubes. A variety of strategies have been developed for surface func- tionalization of CNTs resulting in bonding of different functional groups on their surfaces [4]. The grafting of polymer brushes to a solid surface is a useful technique which provided a versatile tool for surface modification [3]. A thin polymer brush layer on the solid surface is formed, which determines the surface properties. Recently, the sonochemical method was found to functionalize effectively the CNTs [11], as well as to produce polymer grafted carbon nanotubes [3,12]. The ultrasonic cavitation can produce violent collapse of bubbles and high-energy inter-particle colli- sions, generating high temperatures and high pressures together with implosion shock waves and micro jets in the liquid media. http://dx.doi.org/10.1016/j.compscitech.2014.11.004 0266-3538/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Composites Science and Technology 106 (2015) 85–92 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech