Composites Part A: Applied Science and Manufacturing
Effects of surfactant treatment on mechanical and electrical properties of CNT/epoxy nanocomposites
Introduction
As an effective nanoscale reinforcement, carbon nanotubes (CNTs) have attracted great interests in the field of conducting polymer nanocomposites. These nanocomposites should possess good mechanical properties, excellent electrical and thermal conductivities, which are considered useful attributes for many applications in the electronics industry [1], [2], [3]. However, the high aspect ratio and the flexibilities of CNTs [4] along with the van der Waals forces between them cause CNTs to be severely entangled in close packing upon synthesis [5]. Furthermore, the chemically inert nature of CNTs leads to poor dispersibility and weak interfacial interactions with polymer matrix.
Significant research efforts have been devoted to improving the dispersion of CNTs in a polymer matrix. There are two approaches: the mechanical dispersion methods and the surface modification of CNTs based on chemical and physical methods. The mechanical methods include typically ultrasonication in a bath or using a probe sonicator, high shear mixing in a solvent, calendaring and ball milling, as well as combined methods in series or parallel. The mechanical dispersion is carried out to disentangle CNTs from each other by vibratory energy or shear force. The high energy input and the direct mechanical contact with probe sonicators or rigid balls often result in damage and breakage of CNTs into smaller lengths [6], which is considered to be a major disadvantage. The chemical methods are aimed at creating surface functionalities on CNTs, thereby improving their chemical compatibility/interactions with a polymer or solvent, leading to enhanced dispersion. There are two major drawbacks in chemical functionalization: (i) most methods are aggressive, especially the oxidation process using concentrated acids [7], [8], and generate structural defects deteriorating the intrinsic properties of CNTs; (ii) although some milder functionalization processes have been developed, such as UV/ozone treatment or plasmas [9], [10], followed by amine [9], [11], silane [12] or fluorine treatments [13], the limited active sites on CNT surface (mostly at the defects and end caps) may lead to a low efficiency of functionalization, thus altering little the dispersibility of CNTs in a polymer. The non-covalent physical treatments, such as application of surfactants [14], [15], [16], [17] and polymer coating followed by surfactant treatment [18], are particularly attractive because the physical adsorption seldom damages the structure of CNT, nor disturbs the inherent π-bonds of CNTs and thus the electrical properties [17].
Several studies have contributed to studying the effects of surfactant on dispersibility and other property changes of CNTs. The surfactants studied previously include nonionic surfactants such as polyoxyethylene 8 lauryl (CH3(CH2)11(OCH2CH2)7OCH2CH3) [14], nonylphenol ethoxylate (Tergitol NP-7) [19], polyoxyethylene octyl phenyl ether (Triton X-100) [16]; anionic surfactants such as sodium dodecyl sulfate (SDS) [20], [21], [22], [23]; cationic surfactants dodecyl tri-methyl ammoniumbromide (DTAB) [22], cetyltrimethylammounium 4-vinylbenzoate (CTVB) [18]. In particular, a recent study provides a comprehensive review of the mechanisms behind the improved dispersibility of CNTs [16]. The physical adsorption of surfactant on the CNT surface lowered the surface tension of CNT, effectively preventing the formation of aggregates. Furthermore, the surfactant-treated CNTs overcame van der Waals attraction by electrostatic/steric repulsive forces promoted by the surfactant treatment [15], [16]. The efficiency of dispersion depended strongly on the chemistry of the media. It was concluded that in water-soluble polymers such as polyethylene glycol, cationic surfactants had some advantages, whereas in water-insoluble polymers like polypropylene, CNT dispersion was promoted by a nonionic surfactant containing a branched tail [16]. The treatment of nonionic surfactants is based on a strong hydrophobic attraction between the solid surface and the tail group of surfactant. Once the surfactant is adsorbed onto the filler surface, the surfactant molecules are self-assembled into micelles above a critical micelle concentration (CMC).
This paper is part of a large project on CNT dispersion and functionalization for the development of polymer nanocomposites with tailored mechanical/fracture and multi-functional properties. While several studies have shown improved dispersion with surfactant-treated CNTs as summarized above, few studies have reported the resulting properties of the nanocomposites made therefrom. The present study aims specifically at evaluating the effects of surfactant treatment of CNT on the thermomechanical, mechanical and electrical properties of CNT–epoxy nanocomposites. A typical nonionic surfactant, polyoxyethylene octyl phenyl ether (Triton X-100) was chosen as it has been proven to have an ameliorating effect on CNT dispersion [16]. The major mechanical and electrical properties measured from this study were compared with those obtained previously for similar epoxy-based nanocomposites that contained covalently functionalized CNTs via silane treatment [1].
Section snippets
Materials and fabrication of CNT/epoxy nanocomposites
The multi-wall carbon nanotubes (MWNTs, supplied by Iljin Nanotech, Korea) were produced by a chemical vapor deposition (CVD) method, with the specific surface area of 210 m2/g, the length and diameter ranged 10∼15 μm and 10∼20 nm, respectively. Nonionic surfactant, polyoxyethylene octyl phenyl ether (Triton X-100, supplied by VWR International, UK) with the critical micelle concentration (CMC) value of 0.2 mM at 25 °C was used. Two different concentrations of 1 CMC and 10 CMC were studied as the
Surface chemistry and morphology of CNTs
The chemical structure of nonionic surfactant, Triton X-100, is given in Fig. 1. The hydrophobic octyl group of the surfactant can interact with CNT through adsorption, while the hydrophilic segment can interact with the epoxy through hydrogen bonding [14]. Fig. 2 shows the schematic presentations of Triton X-100 molecule and micelle, and the corresponding interactions with CNTs. The long tail (in red color)
Conclusions
The use of a nonionic surfactant Triton X-100 is proposed to treat CNT surface for nanocomposite fabrication, which can serve as a bridge between CNTs and epoxy matrix without disturbing CNT structure or introducing defects. The following can be highlighted from the study:
- (1)
The surfactant treatment introduced prominent changes in CNT surface chemistry: there was a sharp reduction in carbon sp2 bonding along with the concomitant increase in sp3 bonding, with a large increase in oxygen content as
Acknowledgements
The project was supported by the Research Grant Council of Hong Kong SAR (Project No. 614505). Technical assistance from the Materials Characterization and Preparation Facilities (MCPF) and the Advanced Engineering Materials Facilities (AEMF) of HKUST is appreciated.
References (29)
- et al.
Effects of silane functionalization on the properties of carbon nanotube/epoxy nanocomposites
Compos Sci Technol
(2007) - et al.
Shear-induced preferential alignment of carbon nanotubes resulted in anisotropic electrical conductivity of polymer composites
Carbon
(2006) - et al.
Carbon nanotubes for reinforcement of plastics? A case study with poly(vinyl alcohol)
Compos Sci Technol
(2007) - et al.
Electrical conductivity of chemically modified multiwalled carbon nanotube/epoxy composites
Carbon
(2005) - et al.
Surface functionalities of multi-wall carbon nanotubes after UV/ozone and TETA treatments
Carbon
(2006) - et al.
Influence of atomospheric plasma on physicochemical properties of vapor-grown graphite nanofibers
J Colloid Interface Sci
(2005) - et al.
Preparation and characterization of single-walled carbon nanotubes functionalized with amines
Carbon
(2006) - et al.
Functionalization of carbon nanotubes using a silane coupling agent
Carbon
(2006) - et al.
Surface properties of fluorinated single-walled carbon nanotubes
J Fluorine Chem
(2003) - et al.
The role of surfactants in dispersion of carbon nanotubes
Adv Colloid Interface Sci
(2006)
Characterization of multiwall carbon nanotubes and influence of surfactant in the nanocomposite processing
Carbon
Controlling the dispersion of multi-wall carbon nanotubes, in aqueous surfactant solution
Carbon
Effect of the nonionic detergent Triton X-100 on mitochondrial succinate-oxidizing enzymes
Arch Biochem Biophys
Characterization of multi-walled carbon nanotube/phenylethynyl terminated polyimide composites
Compos Part A
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