Polymer nanocomposites based on functionalized carbon nanotubes

Abstract

Carbon nanotubes (CNTs) exhibit excellent mechanical, electrical, and magnetic properties as well as nanometer scale diameter and high aspect ratio, which make them an ideal reinforcing agent for high strength polymer composites. However, since CNTs usually form stabilized bundles due to Van der Waals interactions, are extremely difficult to disperse and align in a polymer matrix. The biggest issues in the preparation of CNT-reinforced composites reside in efficient dispersion of CNTs into a polymer matrix, the assessment of the dispersion, and the alignment and control of the CNTs in the matrix. There are several methods for the dispersion of nanotubes in the polymer matrix such as solution mixing, melt mixing, electrospinning, in-situ polymerization and chemical functionalization of the carbon nanotubes, etc. These methods and preparation of high performance CNT-polymer composites are described in this review. A critical comparison of various CNT functionalization methods is given. In particular, CNT functionalization using click chemistry and the preparation of CNT composites employing hyperbranched polymers are stressed as potential techniques to achieve good CNT dispersion. In addition, discussions on mechanical, thermal, electrical, electrochemical and optical properties and applications of polymer/CNT composites are included.

Introduction

Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima [1], they have received much attention for their many potential applications, such as nanoelectronic and photovoltaic devices [2], [3], superconductors [4], electromechanical actuators [5], electrochemical capacitors [6], nanowires [7], and nanocomposite materials [8], [9]. Carbon nanotubes may be classified as single-walled carbon nanotubes (SWNTs) [10], [11], double-walled carbon nanotubes (DWNTs) [12], [13] or multi-walled carbon nanotubes (MWNTs) [1]. SWNT and DWNT comprise cylinders of one or two (concentric), respectively, graphene sheets, whereas MWNT consists several concentric cylindrical shells of graphene sheets. CNTs are synthesized in a variety of ways, such as arc discharge [10], laser ablation [14], high pressure carbon monoxide (HiPCO) [15], and chemical vapor deposition (CVD) [16], [17]. CNTs exhibit excellent mechanical, electrical, thermal and magnetic properties [18], [19]. The exact magnitude of these properties depends on the diameter and chirality of the nanotubes and whether they are single-walled, double-walled or multi-walled form. Typical properties of CNTs are collected in Table 1 [20], [21], [22], [23], [24], [25].

Because of these excellent properties, CNTs can be used as ideal reinforcing agents for high performance polymer composites. Ajayan et al. [26] reported the first polymer nanocomposites using CNTs as a filler. The number of articles and patents in polymer composites containing CNTs is increasing every year [27]. Various polymer matrices are used for composites, including thermoplastics [28], [29], [30], thermosetting resins [31], [32], liquid crystalline polymers [33], [34], water-soluble polymers [35], conjugated polymers [3], among others. The properties of polymer composites that can be improved due to presence of CNTs include tensile strength [36], [37], tensile modulus [38], [39], toughness [40], glass transition temperature [41], [42], thermal conductivity [43], [44], electrical conductivity [45], [46], solvent resistance [47], optical properties [48], [49], etc.

Progress in polymer/carbon nanotube composite research considered here will included studies on functionalization of CNTs their mechanical, electrical conductivity and optical properties, and applications of polymer/CNT composites.