Article pubs.acs.org/IECR
Preparation of End-Capped Hyperbranched Polyaniline@Carbon Nanotube Hybrids for High‑k Composites with Extremely Low Percolation Threshold and Dielectric Loss Zhixiang Qiang, Guozheng Liang,* Aijuan Gu,* and Li Yuan Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application, Department of Materials Science and Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China S Supporting Information *
ABSTRACT: How to greatly decrease the dielectric loss while maintaining extremely low percolation threshold (fc) is the main target of developing high-k conductor/polymer composites. Here, novel hybridized multiwalled carbon nanotubes (MWCNTs) with coated end-capped hyperbranched polyaniline (EHSiPA), EHSiPA@MWCNT, were developed and embodied into epoxy (EP) resin to produce new high-k composites. Systematic investigations of the structure and dielectric properties showed that the fc of EHSiPA@MWCNT/EP composites is as low as 0.41 wt %; in addition, EHSiPA@MWCNT/EP composites with suitable loadings of EHSiPA have much higher dielectric constants and lower dielectric losses than the MWCNT/EP composite. Specifically, the dielectric constant and loss at 100 Hz for
[email protected]/EP are 1.4 and 6.8 × 10−3 times the values for the MWCNT0.4/EP composite, respectively. To reveal the origin of this, the distributions of space charges of EHSiPA@ MWCNT/EP composites are discussed. This investigation suggests that designing and preparing new conductors with unique structures may provide a way to fabricate high-k composites.
1. INTRODUCTION High-dielectric-constant (high-k) materials are one of hot functional materials because of their ability to store energy and balance the distribution of electric field of cable terminal,1−3 giving them wide potential in many cutting-edge fields. Many works have focused on preparing high-k materials based on conductor/polymer composites because only a small amount of conductor is needed, so the resultant composites have good processing characteristics. However, conductor/ polymer composites generally have high dielectric loss since the insulation−conduction transformation not only produces a high dielectric constant but also brings high dielectric loss. After many attempts, researchers have found that forming a coating on the surfaces of the conductors can effectively reduce the dielectric loss of the composite.4−6 However, this method also brings a drastically enlarged percolation threshold ( fc ≥ 5 wt %), leading to increased difficulty of processing and a deterioration in the mechanical properties.6 Therefore, how to greatly decrease the dielectric loss while maintaining extremely low fc is still a challenge in the development of high-k conductor/polymer composites for applications. This is the target of our investigation reported herein. In this study, novel hybridized conductors (EHSiPA@ MWCNT) made up of multiwalled carbon nanotubes (MWCNTs) and end-capped hyperbranched polyaniline (EHSiPA) were prepared through π−π interactions. On the basis of this, a series of EHSiPA@MWCNT/epoxy (EP) composites were fabricated and found to have not only a higher dielectric constant but also extremely decreased dielectric loss and very low fc. These attractive results were found to be attributed to the unique structure of the hybrids and their effect on the structure of the composites. © 2014 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Materials. MWCNTs with a purity of more than 95% (average outer diameter
