Nanotube-polymer composites

KymakisE, Amaratunga GAJ (2002a). Polymer-nanotube composites burying nanotubes improves their field emission properties. Appl. Phys. Lett. 80 1435-1437. 

V. Scardaci, J. Joimel, J. N. Coleman, Transparent, flexible, and highly conductive thin films based on polymer-nanotube composites, ACS Nano, vol. 3, pp. 714-720, 2009. 

K.I. Winey, R. Haggenmueller, F. Du, and W. Zhou, Polymer-nanotube composites, fibers, and processes, US Patent 7 285 591, assigned to The Trustees of the University of Pennsylvania (Philadelphia, PA), October 23, 2007. 

The purpose of this edited book is to assimilate contributions from a variety of senior scientists in the field of polymer nanotube composites technology to shed light on the recent advances in these commercially important areas of polymer technology. 

Polymer nanotubes composites are now extensively studied. Indeed, one may associate the properties of the polymer with those of nanotubes. This is the case of the mechanical reinforcement of standard polymer for example, but also one can take advantage of the specific electronic properties of the nanotubes. Therefore, we prepared composites with either saturated polymers like polymethylmethacrylate and MWNTs [27]. The electrical conductivity of these compounds as a function of the nanotube content exhibits for example a very low percolation threshold, (a few % in mass) and therefore they can be used as conducting and transparent layers in electronic devices such as Light Emitting Diodes (LEDs). Another type of composite that we have studied is based on the use of a conjugated polymer, polyphenylene-vinylene (PPV) known for its photoluminescence properties and SWNTs. We prepared this composite by mixing SWNTs to the precursor polymer of PPV. The conversion into PPV was subsequently performed by a thermal treatment at 300°C under dynamical vacuum [28],... 

The reaction between toluene 2,4-diisocyanate and carboxylated MWCNTs afforded amido-functionalized nanotubes containing highly reactive isocyanate groups on their surface (Scheme 1.4). The amount of the isocyanate groups was determined by chemical titration and thermogravimetric analysis (TGA) [105]. The modified tubes may constitute promising components to prepare polymer-nanotube composites and coatings [106]. 

Frackowiak E, Khomenko V, Jurewicz K, Lota K, Beguin F. Supercapacitors based on conducting polymers/nanotubes composites. Journal of Power Sources 2006 153 413-418. 

New Microscopy Techniques for a Better Understanding of the Polymer/ Nanotube Composite Properties... 

In the following, we will review several imaging techniques, either based on beam/matter interactions (like electron microscopy either TEM or SEM) or techniques that probe the short distance interactions (like AFM), as they are well suited for the observation of nano-objects and have been extensively used to study nanotubes alone. The principles and the main results on polymer/nanotube composites provided by these imaging techniques (AFM, TEM and SEM) will be presented. 

Despite the results presented above, near-field microscopy has not been extensively used to characterize polymer/nanotube composites However, it can be noticed that AFM is a useful technique to locally probe the mechanical properties of the composites (at the polymer-nanotube interface for example). One possible reason for the small amount of studies by AFM and STM could be that observing the surface only does not permit to obtain much information on the nanotube dispersion state. For that kind of characterization, transmission electron microscopy is a key technique owing to the small nanotube diameter. 

Figure 3.8. (a) Measurement of the 2D apparent distribution of the nanotube curvature radius in polymer/nanotube composites (63). (b) example of 3D nanotube network (64). 

As was detailed in this section, TEM can bring numerous pieces of information regarding the polymer/nanotube composite microstructure. However, it has to be recalled that nanofillers such as nanotubes easily agglomerates and their dispersion state has to be characterised from the micron to the nanometre scale. This is one reason, among others, why Scanning Electron Microscopy is another widely used to characterise polymer/nanotube composites. 

Perhaps the most common method for preparing polymer-nanotube composites has been to mix the nanotubes and polymer in a suitable solvent before evaporating the solvent to form a composite film. One of the benefits of the solution casting method is that agitation of the nanotube powder in a solvent facilitates nanotube de-aggregation and dispersion. Almost all solution processing methods are variations on a general theme which can be summarized in three major steps ... 

The main factor that controls the performance of the composites is the state of dispersion of CNTs in the matrix. Carbon nanotubes can easily form bundles and this aggregation decreases their aspect ratio thus reducing their efficiency as fillers. So, all processing methods used to prepare polymer nanotube composites aim to improve dispersion of CNTs in order to fully exploit the potential of these materials. 

Polymer Nanotube Composites Promises and Current Challenges... 

Two case studies are presented in which polymer nanotube composites are proposed as replacements for conventional materials. We evaluate the technical and economic feasibility of using them as smart materials for strain gauges thus, exploiting their electrical properties, and as structural materials for aircraft panels bringing into play their mechanical properties. Our analysis shows that as new strain gauge materials, polymer nanotube composites offer many advantages. As a possible replacement for aluminum in an aircraft panel, it is found that a hybrid composite of (Epoxy 33% carbon fabric + 30% carbon fibers + 3% CVD-MWNT) is an attractive candidate. 

In order to estimate the theoretical upper bounds for the electrical conductivities of polymer nanotube composites, equation (15.1) was used to calculate conductivity values for model composites based on both SWNT and MWNT. The values are included in Table 15.2 together with the electrical conductivities of individual CNTs as reported in the literature. Although arc-synthesized MWNTs are likely to possess higher conductivities than CVD-grown ones, no distinction is made in the present analysis between the two types due to the unavailability of reliable data. An electrical conductivity of IE-9 S/m is taken to represent the conductivity of a typical polymer matrix. 

Chapter 1 describes the properties and synthesis of nanotubes. It is clear from the properties of the nanotubes that tremendous gains in the properties of the composites can be achieved if the nanotubes and polymer phases are optimally mixed. Chapter 2 reviews the numerous polymer nanotube composite systems reporting superior composite properties and thus justifying the ever-increasing use of nanotubes as fillers for composite materials. Chapter 3 deals with the use of electron microscopy methods along with new... 

Khomenko, V., Frackowiak, E., Szostak, K., and Beguin, F. (2005). Determination of specific capacitance of conducting polymers/nanotubes composite electrodes using different cell configurations. Electrochim. Acta, 50, 2499-506. 

T.S. Jespersen and J. Nygard, Mapping of individual carhon nanotubes in polymer/nanotube composites using electrostatic force microscopy, App. Phys. Lett., 90,183108-183110 (2007). 

In situ polymerisation reactions have also been applied to the preparation of other polymer-nanotube composites. For example, Kumar et al have synthesised new ultra-strong PBO composites in the presence of SWNTs in poly(phosphoric acid) (PPA) by in situ PBO polymerisation. After the polymerisation, PBO-SWNT composite fibres have been spun from the liquid crystalline solutions using dry-jet spinning. 

As we mentioned above, mechanical properties of polymer composites strongly depend on the fabrication and processing approaches used. In this Section, we will discuss and compare mechanical properties of polymer-nanotube composites, which are produced by various processing techniques. 

It should be mentioned that nucleation of crystallinity in the presence of nanotubes may occur in solution casting, melt processing and in situ polymerisation processing of some polymer-nanotube composites. 

In situ polymerisation reactions have also been applied to the preparation of other polymer-nanotube composites. For example, Kumar et have... 

Widely used industrial approaches for the production of polymer fibres and yarns, such as coagulation spinning and electrospinning, have also been utilised for the fabrication of polymer nanotube composites. In coagulation spinning, for example, composite fibres ean be produced by an injection of surfactant-stabilised nanotube dispersion in water into a rotating bath of polymer e.g. PVA) dissolved in water sueh that nanotube and polymer dispersions flowed in the same direction at the point of injection. In this case, polymer molecules replace surfactant molecules on the nanotube surface, thus destabilising the nanotubes dispersion whieh eollapses to form a fibre. These fibres can then be retrieved from the bath, rinsed and dried. ... 

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