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Author

Anna Drury

Other affiliations: University of Texas at Dallas
Bio: Anna Drury is an academic researcher from Trinity College, Dublin. The author has contributed to research in topics: Carbon nanotube & Nanotube. The author has an hindex of 17, co-authored 53 publications receiving 2689 citations. Previous affiliations of Anna Drury include University of Texas at Dallas.


Papers
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TL;DR: In this article, alternating current and direct current (DC) conductivities have been measured in polymer-nanotube composite thin films for a range of concentrations of multi-wall nanotubes in two polymer hosts.
Abstract: Alternating current (ac) and direct current (dc) conductivities have been measured in polymer-nanotube composite thin films. This was carried out for a range of concentrations of multiwall nanotubes in two polymer hosts, poly(m-phenylenevinylene-co-2,5-dioctyloxyp-phenylenevinylene) (PmPV) and polyvinylalcohol (PVA). In all cases the dc conductivity σDC was ohmic in the voltage range studied. In general the ac conductivity displayed two distinct regions, a frequency independent region of magnitude σ0 at low frequency and a frequency dependent region at higher frequency. Both σDC and σ0 followed a percolation scaling law of the form σ∝(p−pc)t with pc=0.055% by mass and t=1.36. This extrapolates to a conductivity of 1×10−3 S/m for 100% nanotube content. Such a low value reflects the presence of a thick polymer coating, resulting in poor electrical connection between tubes. This leads to the suggestion that charge transport is controlled by fluctuation induced tunneling. In the high frequency regime the cond...

748 citations

Journal ArticleDOI
TL;DR: In this paper, a conjugated luminescent polymer, poly(m-phenylenevinylene-co-2,5-dioctoxyp-phenylonvinylene) (PmPV), was used as an emissive layer in an organic light-emitting diode (LED).
Abstract: As research progresses towards smaller and more efficient devices, the need to develop alternative molecular scale electronic materials becomes apparent. Integrated electronic component fabrication from organics has been recognized theoretically as the ultimate goal. In order to gain a comprehensive insight into these materials, extensive research has been carried out on conjugated carbon systems over the last few decades to optimize their optical and electrical properties. For example, doping polyacetylene with I2 has been shown to result in a large increase in conductivity compared to the pristine material. However, doping polymers tends to retard their optical properties as regards luminescence by reducing their bandgaps and introducing trapping sites such as solitons, polarons, or bipolarons. The simple lesson over the years is that if materials are to be considered for luminescence, doping should not be carried out despite the desire to improve charge transport properties. We report here the first physical adopingo, to use the traditional term, using small concentrations of multiwalled nanotubes in a conjugated luminescent polymer, poly(m-phenylenevinylene-co-2,5-dioctoxyp-phenylenevinylene) (PmPV), in a polymer/nanotube composite. This can increase electrical conductivity of the polymer by up to eight orders of magnitude. The nanotubes appear to act as nanometric heat sinks, preventing the buildup of large thermal effects, caused either optically (photobleaching) or electrically, which degrade these conjugated systems. We also report that electroluminescence was achieved from an organic light-emitting diode (LED) using the composite as the emissive layer in the device. Since initial work on conjugated systems, attempts have been made to find an area where polymers and/or fullerenes could be used as active semiconductor components. Although many new and interesting materials have been synthesized to this end, very few have found a practical application. One exception is polyphenylenevinylene (PPV), first reported by Burroughes et al. as being the light-emitting semiconductor in a Schottky diode. This encouraged scientists to study a wide variety of conjugated systems, including derivatives of this polymer, in order to optimize the efficiency of light emission from such devices. Polymers for use in LEDs must possess a number of important qualities. A high quantum yield of photoluminescence is necessary and the material must remain undoped, as dopants act as trapping sites, quenching the radiative decay of excitons. It is essential therefore to find a polymer that is reasonably conductive while maintaining its luminescent properties. Most undoped polymers possess a very low conductivity and so require high aturn-ono fields to generate sufficient carriers in order to produce the excitons, which decay radiatively. This is, in practical terms, very inefficient as fields generally induce large thermal effects, consequently causing device breakdown. There are other problems that must be addressed, but elimination of these very basic ones should substantially improve efficiencies and soon lead to applications for these polymers. The polymer used in our studies is PmPV, whose structure is a variation of the more common PPV. In this case the substitution pattern leads to dihedral angles in the chain and, according to molecular mechanics energy minimization calculations, the polymer chain tends to coil, forming a helical structure. The calculated diameter of this helix in vacuum is ca. 20 Š, whilst the pitch is ca. 6 Š. Multiwalled nanotubes were produced by the arc discharge method, resulting in multiwalled nanotubes of 20 nm average diameter and lengths between 500 nm and 1.5 mm. The nanotube powder and PPV were mixed together in toluene and sonicated briefly. It is probable that the coiled polymer conformation allows it to surround layers of nanotubes, permitting sufficiently close intermolecular proximity for p±p interaction to occur. The color change was dramatic in that the polymer has a bright yellow color while the composite, at high nanotube concentrations, possesses a deep green color. Photoluminescence studies were carried out using an Ar laser at the pump wavelength of 457 nm. Electrical conductivity was measured using a twopoint probe sandwich geometry and Pt electrodes. The LED was fabricated by casting the composite onto indium tin oxide (ITO) then sputtering an aluminum electrode on top. As the polymer structure possesses helicity, it is not surprising that it is able to wrap itself around the nanotubes and keep them suspended in solution indefinitely. The actual texture of the composite can be observed in Figure 1,

589 citations

Journal ArticleDOI
TL;DR: In this article, a conjugated, semiconducting polymer was examined by a range of microscopic and spectroscopic techniques, to gain a greater understanding of the binding between polymer and nanotubes.
Abstract: Production of stable polymer−nanotube composites depends on good wetting interaction between polymer and nanotube, which is polymer specific, and depends in particular on chain conformation. In this paper, we examine this interaction for a conjugated, semiconducting polymer by a range of microscopic and spectroscopic techniques, to gain a greater understanding of the binding. Several interesting effects are observed, including an order to the interaction between the polymer and nanotube, the tendency of defects in the nanotube structure to nucleate crystal growth, and substantial changes in the spectroscopic behavior of the polymer due to the effect of the nanotubes on polymer conformation. This is substantiated by computational modeling, which demonstrates that these conformational modifications are due to the interaction with the nanotubes.

232 citations

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TL;DR: In this paper, a one-step, high-yield, nondestructive purification and processing method for multiwalled carbon nanotubes (MWNT) containing soot using a conjugated organic polymer host was described.
Abstract: We have described a one-step, high-yield, nondestructive purification and processing method for multiwalled carbon nanotube (MWNT) containing soot using a conjugated organic polymer host. This host selectively suspends nanotubes relative to impurities. The fraction of available MWNTs suspended can be measured using electron paramagnetic resonance (EPR) and rises with increasing polymer mass before saturating at approximately 50% by mass for a soot to polymer mass ratio of 1:5. Thermogravimetric analysis can then be used to calculate the mass of nanotubes suspended and hence the purity of the original soot. Furthermore, this allows the calculation of numerical constants relating the EPR signal intensity to the nanotube mass, allowing the routine calculation of nanotube content. Finally the host polymer was removed by filtration, giving 91% pure nanotube material. In this case a yield of 17% pristine nanotubes was reclaimed from the soot. Full optimization of this process could lead to yields of up to 40%.

119 citations


Cited by
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Journal ArticleDOI
TL;DR: Department of Materials Science, University of Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Triesteadays.
Abstract: Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

3,886 citations

Journal ArticleDOI
01 Aug 2006-Carbon
TL;DR: In this article, a review of the progress to date in the field of mechanical reinforcement of polymers using nanotubes is presented, and the most promising processing methods for mechanical reinforcement are discussed.

3,770 citations

Journal ArticleDOI
TL;DR: The direct synthesis of three-dimensional foam-like graphene macrostructures, which are called graphene foams (GFs), by template-directed chemical vapour deposition is reported, demonstrating the great potential of GF/poly(dimethyl siloxane) composites for flexible, foldable and stretchable conductors.
Abstract: [Chen, Zongping; Ren, Wencai; Gao, Libo; Liu, Bilu; Pei, Songfeng; Cheng, Hui-Ming] Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

3,517 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the current understanding of carbon nanotubes and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT-based functionalization on the properties of polymers.
Abstract: Carbon nanotubes (CNTs) hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. Ever-increasing interest in applying CNTs in many different fields has led to continued efforts to develop dispersion and functionalization techniques. To employ CNTs as effective reinforcement in polymer nanocomposites, proper dispersion and appropriate interfacial adhesion between the CNTs and polymer matrix have to be guaranteed. This paper reviews the current understanding of CNTs and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT dispersion and functionalization on the properties of CNT/polymer nanocomposites. The fabrication techniques and potential applications of CNT/polymer nanocomposites are also highlighted.

2,849 citations

Journal ArticleDOI
TL;DR: In this paper, an extended account of the various chemical strategies for grafting polymers onto carbon nanotubes and the manufacturing of carbon-nanotube/polymer nanocomposites is given.

2,766 citations