The addition of nitrophenyl groups to the surface of few-layer epitaxial graphene (EG) by the formation of covalent carbon-carbon bonds changed the electronic structure and transport properties of the EG from near-metallic to semiconducting.

Covalent derivatization of the acidic functional groups in oxidized graphite with octadecylamine renders graphite soluble in common organic solvents. Atomic force microscopic characterization of the soluble species supports the idea that the solutions consist of single and few layer graphene sheets, and we report the first solution properties of graphite.

The increased heat generated in high density electronics has intensified the search for advanced thermal interface materials (TIMs) and prompted fundamental studies at the nanoscale level to develop filler materials with enhanced thermal performance. [1][2][3][4] Single-walled carbon nanotubes (SWNTs) considerably improve the heat transport in polymer composites as a result of their one-dimensional (1D) structure, high thermal conductivity and high aspect ratio. [5][6][7][8][9][10][11][12] Recently, two-dimensional (2D) nanostructures such as graphite nanoplatelets (GNPs), have emerged as a promising filler in polymer matrices [13][14][15][16][17][18][19] and it has been shown that they provide even higher thermal conductivity enhancement than SWNTs. [16] In this study we combine 1D-SWNTs and 2D-GNPs to prepare a series of hybrid graphitic nanofillers and we observe a synergistic effect between the GNPs and SWNTs in the enhancement of the thermal conductivity of epoxy composites to the point that at certain filler loadings the hybrid composition outperforms composites utilizing pure GNP or SWNT fillers. The increased thermal conductivity is ascribed to the formation of a more efficient percolating nanoparticle network with significantly reduced thermal interface resistances. The idea of using a hybrid filler comprised of two or more traditional filler materials has already been explored in the literature and it has been demonstrated that improved composite performance can be achieved by combining the advantages of each filler. [20,21] Commercially available thermal greases and adhesives often utilize several components to achieve the desired combination of thermal and electrical conductivities, viscosity and low coefficient of thermal expansion. In our study, we utilize two different nanostructured graphitic fillers for incorporation into epoxy resin: purified SWNTs and graphite nanoplatelets (GNPs) comprised of few graphene layer G n , where n $ 4. The SWNT component of the hybrid filler is electric arc produced purified SWNTs with a typical length of 0.3-1.0 mm and an average diameter of 1.4 nm. The purification process [22] leaves the SWNTs ends and side-walls functionalized with carboxylic acid groups and this facilitates their homogeneous dispersion into the polymer matrix. In addition, the epoxy curing process is accompanied by a cross-linking reaction between the carboxylic acid groups of the SWNTs and the epoxy groups of the polymer, [23] thus improving the integration of SWNTs into the polymer matrix. GNPs are typically prepared by intercalation and exfoliation of graphite; [24][25][26][27][28][29] and by control of the exfoliation conditions we were able to obtain GNPs comprised of 2 to 8 graphene layers with a lateral dimension of 200-1000 nm and an aspect ratio in the range of 50 to 300. [16] This was achieved by thermal shock exfoliation of natural graphite flakes at 800 8C [25,26] followed by high shear mixing and sonication in order to separate the exfoliated graphite flakes into nanoplatelets.[...

In order to engineer a band gap into graphene, covalent bond-forming reactions can be used to change the hybridization of the graphitic atoms from sp 2 to sp 3 , thereby modifying the conjugation length of the delocalized carbon lattice; similar side-wall chemistry has been shown to introduce a band gap into metallic single-walled carbon nanotubes. Here we demonstrate that the application of such covalent bond-forming chemistry modifies the periodicity of the graphene network thereby introducing a band gap (∼0.4 eV), which is observable in the angle-resolved photoelectron spectroscopy of aryl-functionalized graphene. We further show that the chemically-induced changes can be detected by Raman spectroscopy; the in-plane vibrations of the conjugated π-bonds exhibit characteristic Raman spectra and we find that the changes in D, G, and 2D-bands as a result of chemical functionalization of the graphene basal plane are quite distinct from that due to localized, physical defects in sp 2 -conjugated carbon.

We report an approach to the development of advanced structural composites based on engineered multiscale carbon nanotube-carbon fiber reinforcement. Electrophoresis was utilized for the selective deposition of multi- and single-walled carbon nanotubes (CNTs) on woven carbon fabric. The CNT-coated carbon fabric panels were subsequently infiltrated with epoxy resin using vacuum-assisted resin transfer molding (VARTM) to fabricate multiscale hybrid composites in which the nanotubes were completely integrated into the fiber bundles and reinforced the matrix-rich regions. The carbon nanotube/carbon fabric/epoxy composites showed approximately 30% enhancement of the interlaminar shear strength as compared to that of carbon fiber/epoxy composites without carbon nanotubes and demonstrate significantly improved out-of-plane electrical conductivity.

We present a study on the electronic behavior of films of as-prepared and purified single-walled carbon nanotubes (SWNTs) and demonstrate the important role that chemical functionalization plays in modifying their electronic properties, which in turn throws further light on the mechanism of action of SWNT-based sensors. Films of electric arc SWNTs were prepared by spraying, and optical spectroscopy was used to measure the effective film thickness. The room-temperature conductivities (sigma(RT)) of thin films deposited from as-prepared and purified SWNTs are in the range sigma(RT) = 250-400 S/cm, and the nonmetallic temperature dependence of the conductivity indicates the presence of tunneling barriers, which dominate the film conductivity. Chemical functionalization of SWNTs with octadecylamine (ODA) and poly(m-aminobenzenesulfonic acid) (PABS) significantly decreases the conductivity; sigma(RT) = 3 and 0.3 S/cm for SWNT-ODA and SWNT-PABS, respectively.

We report a chemical processing technology that allows the continuous spinning of single-walled carbon nanotubes (SWNTs)-nylon 6 (PA6) fibers by the in-situ polymerization of caprolactam in the presence of SWNTs, which simultaneously optimizes the morphology of the composite. We show that caprolactam is an excellent solvent for carboxylic-acid-functionalized SWNTs (SWNT-COOH) and that this allows the efficient dispersal of the SWNTs and subsequent grafting of PA6 chains to the SWNTs through condensation reactions between the carboxylic-acid group on SWNT-COOH and the terminal amine group of PA6. The existence of a graft copolymer between the PA6 chains and the SWNTs is demonstrated by IR, TGA, and AFM studies, and we show that the solubility of the polymerized material in formic acid is controlled by the degree of graft copolymerization. The amount of grafted PA6 chains that are attached to the SWNTs can be adjusted by controlling the concentration of the initiator (6-aminocaproic acid). The process leads to a uniform dispersion of the SWNTs, and the presence of the graft copolymer increases the polymer/SWNT compatibility while strengthening the interfacial interaction between the nanotube and matrix. The Young's modulus, tensile strength, and thermal stability of the SWNT-reinforced composite fibers produced by this process are significantly improved.

Single-walled carbon nanotube (SWNT) reinforced polymer composite membranes have been fabricated using the electrospinning technique. Nanofibers with a diameter in the range 50−100 nm were obtained by electrospinning SWNT-filled polystyrene composites. TEM observations revealed incorporation of small SWNT bundles oriented parallel to the nanofiber axis. As-prepared (AP) and ester (EST) functionalized SWNTs have been electrospun with polyurethane (PU) to demonstrate the effect of the chemical functionalization of SWNTs on the mechanical properties of SWNT-reinforced composites. The tensile strength of EST-SWNT-PU membranes is enhanced by 104% as compared to electrospun pure polyurethane membranes, while an increase of only 46% was achieved incorporating AP−SWNT in the polyurethane matrix. The tangent moduli of AP-and EST-SWNT-PU membranes were found to be respectively 215% and 250% higher than the control polyurethane membranes.