Mechanical and Electrical Characterization of Hybrid Carbon Nanotube Sheet-Graphene Nanocomposites for Sensing Applications

The unique mechanical and electrical properties of carbon nanotubes and graphitic structures have drawn extensive attention from researchers over the past two decades. The electro-mechanical behavior of these structures and their composites, in which electrical resistance changes when mechanical deformation is applied facilitates their use in sensing applications. In this work, carbon nanotube sheet- epoxy nanocomposites with the matrix modified with various contents of coarse and fine graphene nanoplatelets are fabricated. The addition of a secondary filler results in improvements of both electrical and mechanical properties. In addition, with the inclusion of the second filler, change in resistivity with mechanical deformation (manifested by gauge factor) is significantly enhanced. Nanocomposite with 5 wt. % coarse graphene platelets achieved is the most effective resistivity-strain behavior and largest gauge factor. Similar trend in variation of gauge factor variation was observed for fine graphene nanoplatelet - nanotube sheet nanocomposites. An analytical model for explaining these observations, incorporating strain and the effect of second filler, is developed. Sensors fabricated using these hybrid nanocomposites can be potentially used in damage sensing of aerospace carbon-fiber composites

Recent advances in carbon-based polymer nanocomposites for electromagnetic interference shielding

Carbon-based nanoparticles have recently generated a great attention, as they could create polymer nanocomposites with enhanced transport properties, overcoming some limitations of electrically-conductive polymers for high demanding sectors. Particular importance has been given to the protection of electronic components from electromagnetic radiation emitted by other devices. This review considers the recent advances in carbon-based polymer nanocomposites for electromagnetic interference (EMI) shielding. After a revision of the types of carbon-based nanoparticles and respective polymer nanocomposites and preparation methods, the review considers the theoretical models for predicting the EMI shielding, divided in those based on electrical conductivity, models based on the EMI shielding efficiency, on the so-called parallel resistor-capacitor model and those based on multiscale hybrids. Recent advances in the EMI shielding of carbon-based polymer nanocomposites are presented and related to structure and processing, focusing on the effects of nanoparticle’s aspect ratio and possible functionalization, dispersion and alignment during processing, as well as the use of nanohybrids and 3D reinforcements. Examples of these effects are presented for nanocomposites with carbon nanotubes/nanofibres and graphene-based materials. A final section is dedicated to cellular nanocomposites, focusing on how the resulting morphology and cellular structures may generate lightweight multifunctional nanocomposites with enhanced absorption-based EMI shielding propertiesPostprint (author's final draft

Composite Materials reinforced by Carbon Nanotubes

The work of this Ph.D. thesis has been realised in the field of a promising and largely studied technological material: the carbon nanotubes (CNTs). Since 1991 a large number of attempts have been conducted, trying to exploit the outstanding potential of this carbonaceous material, in order to improve the properties of several matrices. The most important application is the production of polymer matrices composites (PMCs), but in last decades an increasing number of metal matrix ones (MMCs) have been presented and recently also ceramic matrix (CMCs) applications have been attempted. Despite massive efforts focused on CNTs-composites, the potential of employing this reinforcement materials has not yet been fully exploited. This lack is substantially due to the difficulties associated with the dispersion of entangled carbon nanotubes during processing and poor interfacial interaction between CNTs and matrix materials. Because of these reasons the very first aspect of this work has been the study of the dispersion state of nanotubes. The aim of the experiments was not only to obtain a good dispersion and distribution of the CNTs, but also to evaluate their dispersion grade. Indeed, due to their nanosize and to their carbonaceous nature, few simple experimental techniques result suitable for this purpose. The second part of the work consisted in the application of the carbon nanotubes to the production of new materials for technological applications, with improved mechanical properties. Three composite materials with different matrices have been designed, developed and produced: a polymer matrix composite, a ceramic matrix and a metal matrix one. For PMCs a polyvinyl butyral matrix has been used and the composites were obtained by a deeply studied technique: the tape casting technology. The same approach was also used in the case of CMCs: tape casted silicon carbide matrix composites reinforced by carbon nanotubes have been produced. Finally a third matrix has been experimented: MMCs were investigated starting from pure aluminium powders. For Al matrix composites a particular technique was used: the sintering was obtained starting from a powder metallurgy approach and exploiting electric current and pressure (Electric Current Assisted Sintering approach). For all the three different composite materials, after the development of the production route and the preparation of several specimens, a characterization step followed. The materials were characterized in terms of physical properties, morphology and microstructure, and mechanical behaviou

Advanced Mechanical Modeling of Nanomaterials and Nanostructures

This reprint presents a collection of contributions on the application of high-performing computational strategies and enhanced theoretical formulations to solve a wide variety of linear or nonlinear problems in a multiphysical sense, together with different experimental studies

Biomimetic route to hybrid nano-Composite scaffold for tissue engineering

Hydroxyapatite-poly(vinyl) alcohol-protein composites have been prepared by a biomimetic route at ambient conditions, aged for a fortnight at 30±2°C and given a shape in the form of blocks by thermal cycling. The structural characterizations reveal a good control over the morphology mainly the size and shape of the particles. Initial mechanical studies are very encouraging. Three biocompatibility tests, i.e., hemocompatibility, cell adhesion, and toxicity have been done from Shree Chitra Tirunal, Trivandrum and the results qualify their standards. Samples are being sent for more biocompatibility tests. Optimization of the blocks in terms of hydroxyapatite and polymer composition w.r.t the applications and its affect on the mechanical strength have been initiated. Rapid prototyping and a β-tricalcium – hydroxyapatite combination in composites are in the offing

The Strain Dependent Dielectric Behaviour of Carbon Black Filled Natural Rubber

PhDThe behaviour of filled elastomer materials is of practical importance in many fields of engineering science. The exact mechanisms that result in increases in the physical behaviour such as the modulus, strength, damping or toughness of the resulting composite materials is still being widely debated in the academic literature. In this work, a new and novel approach has been developed to study the reinforcing mechanisms of such composite systems using dielectric spectroscopic measurements of the filled elastomer materials. The materials used are mostly Natural Rubber (NR) filled with either carbon black (CB) or silica. Initially broadband dielectric spectroscopy (ranging from around 0.1 Hz to 0.3 THz) on NR/CB composites was developed using a wide range of different technologies that included impedance measurements, microwave testing and quasi-optical free space measurements. The carbon black makes a large contribution to the permittivity measured using the impedance method as a consequence of filler percolation effects. At higher frequencies, tested using either of the other two technologies, the measured permittivity shows an increase almost proportional to the filler volume fraction. By examining different types of carbon black, this behaviour was found to be independent of the filler surface area. The polymer dynamics of NR filled with either CB or silica has also been studied in detail using temperature-domain impedance spectroscopy. A technique has been developed to measure the bulk glass transition temperature, Tg from the alpha relaxations. The bulk Tg of the filled NR compounds is, to within the accuracy of the experiment, almost totally unchanged by the incorporation of the filler materials. This suggests that the polymer dynamics of the NR chains around the filler surface are either very similar in behaviour to the bulk matrix polymer or at least they have too small a volume to be measured as a change in the bulk properties. An entirely new technique was developed to measure the permittivity of natural rubber filled with either CB or silica under strain. This required the building of a simultaneous II dielectric and mechanical spectroscopy facility. Both the real and imaginary part of the permittivity decrease when the strain is larger than 1% for all the filled samples. This decrease comes from the deactivation of the dipoles around the filler-polymer interface with strain. The electrical permittivity versus strain behaviour follows a very similar softening effect to the mechanical Payne and Mullins effects albeit to a much greater extent and at a different level of strain. This allows an independent measure to be made of changes in the filler network structure with strain and this facilitates a better understanding of the actual network structures that might exist. The dielectric behaviour versus strain relationship presents an opportunity to develop novel strain sensors. The prototype capacitance strain sensors made using a carbon black filled NR exhibited a much larger sensitivity when compared to other recently reported sensors.CSC scholarship provided by the government of P.R.Chin

Nano- and Microcomposites for Electrical Engineering Applications

In a dedicated Special Issue, the journal Polymers has compiled papers on the current trends and research directions within the preparation, characterization and application of polymer-based composite materials in electrical engineering applications. In recent times, this type of material has evolved to become one of the most thoroughly investigated materials, stimulated by the demand for the resource-efficient assembly of generators, transformers, communication devices, etc. Novel composites are to be used as insulating materials with high thermal conductivity and excellent temperature stability, through which premature ageing and degradation of devices shall be avoided or at least reduced. This Special Issue comprises twelve contributions by internationally renowned researchers; to mention Petru V. Nothinger (University Politehnica of Bucharest), Alun S. Vaughan (University of Southampton), Stanislaw M. Gubanski (Chalmers University of Technology), Michael Muhr (Graz University of Technology), Johan J. Smit (TU Delft), and Ulf W. Gedde (KTH Royal Institute of Technology) as prominent examples. The state-of-the-art research and technology of the area ‘micro- and nanocomposites for electrical engineering applications’ has been summarized in three review articles, while the current research trends and the development and characterization of novel materials have been described in eight original research articles. Stimulated by the vivid current interest in this topic, this Special Issue of Polymers has additionally been compiled in a book version

Electrophoretic deposition of carbon nanotubes: recent progress and remaining challenges

Electrophoretic deposition (EPD) is a powerful technique to assemble carbon nanotube (CNT) coatings and composite films with controlled architectures. This comprehensive review of the EPD of CNTs and CNT-containing composites focuses on achievements within the last 15 years and ongoing challenges. Stable CNT suspensions are a pre-requisite for successful EPD and have been prepared by a variety of strategies, discussed here. The resulting film microstructure is determined by the initial feedstock, the suspension, and the EPD approach applied, as well as a variety of EPD processing parameters. Nanocomposites can be prepared via co-deposition, sequential deposition, or post-deposition treatments, to introduce metallic, ceramic or polymeric phases. There are numerous potential applications for both homogeneous and patterned CNT films, including as structural reinforcements for composites, as field emission, energy storage and conversion devices, as well as in biomedical applications. The advantages and disadvantages of EPD processing in these contexts are discussed

Carbon Nanotubes

Since their discovery in 1991, carbon nanotubes have been considered as one of the most promising materials for a wide range of applications, in virtue of their outstanding properties. During the last two decades, both single-walled and multi-walled CNTs probably represented the hottest research topic concerning materials science, equally from a fundamental and from an applicative point of view. There is a prevailing opinion among the research community that CNTs are now ready for application in everyday world. This book provides an (obviously not exhaustive) overview on some of the amazing possible applications of CNT-based materials in the near future

EFFECTS OF DIVERSE VARIABLES ON RESISTIVITY, RHEOLOGY, AND NETWORK VISUALIZATION OF ELECTRICALLY CONDUCTIVE EPOXY-CNT COMPOSITES

The addition of high-aspect ratio nanometric conductive fillers (i.e., carbon nanotubes [CNTs]) to an epoxy matrix has been shown to improve electrical conductivity by many orders of magnitude. These nanocomposites, well-suited for electrostatic dissipation and electromagnetic interference applications, are of intense interest to the aerospace industry where epoxy resins are already widely employed. Future adoption and commercial production efforts are limited by a lack of understanding of how electrical and rheological properties of uncured mixtures relate to the finished composite, how they change throughout the epoxy curing process, or how these materials are affected by extreme operating environments. To bridge these gaps, the viscosity and electrical properties of uncured mixtures were characterized and correlated to cured values, potentially allowing for quality control at a point in the production process where remediation is possible. Rare-earth oxide nanoparticles, europium-doped yttria, were synthesized into CNT walls, enhancing the contrast of the conductive network in scanning electron microscopy and micro-computed tomography while also granting deep-UV fluorescence. Lastly, in-situ electrical measurements of an epoxy-CNT composite were conducted under simulated low-earth orbit conditions with instantaneous decreases in resistivity as large as 60% being documented.DOD SpaceLieutenant Commander, United States NavyApproved for public release. Distribution is unlimited