Growth and Properties of Carbon Microcoils and Nanocoils

Various types of coiled carbon filaments have been synthesized using chemical vapor deposition and other methods. These carbon filaments exhibit unique electrical and mechanical properties due to their versatile shapes and structures. To form coiled shapes, different types of catalyst compositions and reactive gases have been explored. Generally, coiled carbon filaments are classified by coil diameter and shape (e.g., microcoil and nanocoil). In this review, coiled carbon filaments are classified into three growth mechanism categories: (1) bidirectional double helical growth; (2) bidirectional twisted growth; and (3) tip single helical or twisted growth. Next, their synthesis methods and hypothetical growth mechanisms are discussed. Then, their electrical and mechanical properties are listed. Finally, potential applications and uses of coiled carbon filament are mentioned

Real-time strain monitoring and damage detection of composites in different directions of the applied load using a microscale flexible Nylon/Ag strain sensor

Composites are prone to failure during operating conditions and that is why vast research studies have been carried out to develop in situ sensors and monitoring systems to avoid their catastrophic failure and repairing cost. The aim of this research article was to develop a flexible strain sensor wire for real-time monitoring and damage detection in the composites when subjected to operational loads. This flexible strain sensor wire was developed by depositing conductive silver (Ag) nanoparticles on the surface of nylon (Ny) yarn by electroless plating process to achieve smallest uniform coating film without jeopardizing the integrity of each material. The sensitivity of this Nylon/Ag strain sensor wire was calculated experimentally, and gauge factor was found to be in the range of 21–25. Then, the Nylon/Ag strain sensor wire was inserted into each composite specimen at different positions intentionally during fabrication depending upon the type of damage to detect. The specimens were subjected to tensile loading at a strain rate of 2 mm/min. Overall mechanical response of composite specimens and electrical response signal of the Nylon/Ag strain sensor wire showed good reproducibility in results; however, the Nylon/Ag sensor showed a specific change in resistance in each direction because of the respective position. The strain sensor wire designed not only monitored the change in the mechanical behavior of the specimen during the elongation and detected the strain deformation but also identified the type of damage, whether it was compressive or tensile. This sensor wire showed good potential as a flexible reinforcement in composite materials for in situ structural health monitoring applications and detection of damage initiation before it can become fatal

Nanotechnology and Development of Strain Sensor for Damage Detection

Composite materials, having better properties than traditional materials, are susceptible to potential damage during operating conditions, and this issue is usually not found until it is too late. Thus, it is important to identify when cracks occur within a structure, to avoid catastrophic failure. The objective of this chapter is to fabricate a new generation of strain sensors in the form of a wire/thread that can be incorporated into a material to detect damage before they become fatal. This microscale strain sensor consists of flexible, untwisted nylon yarn coated with a thin layer of silver using electroless plating process. The electromechanical response of this sensor wire was tested experimentally using tensile loading and then verified numerically with good agreement in results. This flexible strain sensor was then incorporated into a composite specimen to demonstrate the detection of damage initiation before the deformation of structure becomes fatal. The specimens were tested mechanically in a standard tensometer machine, while the electrical response was recorded. The results were very encouraging, and the signal from the sensor was correlated perfectly with the mechanical behavior of the specimen. This showed that these flexible strain sensors can be used for in situ structural health monitoring (SHM) and real-time damage detection applications

Optical Properties of Carbon Microcoils

Carbon microcoils (CMCs) have emerged as versatile material artifacts for a variety of applications due to their helical and spiral structures. Embedded in matrix, CMCs have already been demonstrated for their potential tactile/proximity sensor application. In this study, CMCs were prepared using a conventional chemical vapor deposition method, and then were functionalized with octadecylamine. Upon photoexcitation, the functionalized CMCs exhibited photoluminescence in the visible region, which has never been found before. Similar to carbon based nanoparticles, the photoluminescence of CMCs was attributed to electron-hole radiative recombination after surface passivation. The results suggested that this kind of fluorescent functionalized CMCs might be used as a promising class of optical agents for biological applications

Growth and Properties of Carbon Microcoils and Nanocoils

Various types of coiled carbon filaments have been synthesized using chemical vapor deposition and other methods. These carbon filaments exhibit unique electrical and mechanical properties due to their versatile shapes and structures. To form coiled shapes, different types of catalyst compositions and reactive gases have been explored. Generally, coiled carbon filaments are classified by coil diameter and shape (e.g., microcoil and nanocoil). In this review, coiled carbon filaments are classified into three growth mechanism categories: (1) bidirectional double helical growth; (2) bidirectional twisted growth; and (3) tip single helical or twisted growth. Next, their synthesis methods and hypothetical growth mechanisms are discussed. Then, their electrical and mechanical properties are listed. Finally, potential applications and uses of coiled carbon filament are mentioned

Mechanical properties of carbon black/poly (ε-caprolactone)-based tissue scaffolds

Carbon black (CB) spherical particles were added to poly(ε-caprolactone) (PCL) polymer to produce strong synthetic tissue scaffolds for biomedical applications. The objective of this paper is to study the mechanical behavior of CB/PCL-based nanocomposites using experimental tests, multi-scale numerical approaches, and analytical models. The mechanical properties of CB/PCL scaffolds were characterized using thermal mechanical analysis and results show a significant increase of the elastic modulus with increasing nanofiller concentration up to 7 wt%. Conversely, finite element computations were performed using a simulated microstructure, and a numerical model based on the representative volume element (RVE) was generated. Thereafter, Young's moduli were computed using a 3D numerical homogenization technique. The approach takes into consideration CB particles’ diameters, as well as their random distribution and agglomerations into PCL. Experimental results were compared with data obtained using numerical approaches and analytical models. Consistency in the results was observed, especially in the case of lower CB fractions

Thermal Conductivity Improvement in Carbon Nanoparticle Doped PAO Oil: An Experimental Study

The present work involves a study on the thermal conductivity of nanoparticle-oil suspensions for three types of nanoparticles, namely, carbon nanotubes(CNTs), exfoliated graphite (EXG), and heat treated nanofibers (HTT) with PAO oil as the base fluid. To accomplish the above task, an experimental analysis is performed using a modern light flash technique (LFA 447) for measuring the thermal conductivity of the three types of nanofluids, for different loading of nanoparticles. The experimental results show a similar trend as observed in literature for nanofluids with a maximum enhancement of approximately 161% obtained for the CNT-PAO oil suspension. The overall percent enhancements for different volume fractions of the nanoparticles are highest for the CNT-based nanofluid, followed by the EXG and the HTT. The findings from this study for the three different types of carbon nanoparticles can have great potential in the field of thermal management

Carbon Nanoadditives to Enhance Latent Energy Storage of Phase Change Materials

Latent energy storage capacity was analyzed for a system consisting of carbon nanoparticlesdopedphase changematerials (PCMs). Three types of samples were prepared by doping shell wax with single wall carbon nanotubes(SWCNTs), multiwall CNTs, and carbon nanofibers. Differential scanning calorimetry was used to measure the latent heat of fusion. The measured values of latent heat for all the samples showed a good enhancement over the latent heat of pure wax. A maximum enhancement of approximately 13% was observed for the wax/SWCNT composite corresponding to 1% loading of SWCNT. The change in latent heat was modeled by using an approximation for the intermolecular attraction based on the Lennard-Jones potential. A theoretical model was formulated to estimate the overall latent energy of the samples with the variation in volume fraction of the nanoparticles. The predicted values of latent energy from the model showed good agreement with the experimental results. It was concluded that the higher molecular density of the SWCNT and its large surface area were the reasons behind the greater intermolecular attraction in the wax/SWCNT composite, which resulted in its enhanced latent energy. The novel approach used to predict the latent heat of fusion of the wax/nanoparticle composites has a particular significance for investigating the latent heat of PCM with different types of nanoparticle additives

Interfacial and Capillary Pressure Effects on the Thermal Performance of Wax/Foam Composites

A numerical investigation study was performed to study the phase change behavior of wax/foam composite encapsulated in an aluminum casing. Two types of foam materials, namely, aluminum and carbon, were infiltrated with paraffin wax. The progress of melt interface and temperature distribution within the encapsulated composite was analyzed using computational fluid dynamics software (CFD). A two-energy equation model was implemented in the CFD software through the use of user-defined function (UDF). Interfacial effects influencing the heat transfer process at the casing-composite junction and between the wax-foam surfaces within the composite were addressed through the use of separate UDF. In addition, the effect of capillary pressure developed within the foam matrix was incorporated using an area ratio parameter. The contact resistance at the foam-casing interface and the capillary pressure had a major influence on the thermal behavior of the system. These two factors lowered the heat transfer rate considerably, and the melting area was reduced by more than 30%. The temperature profiles for the foam material showed a different pattern as compared to the temperature within the wax, which was due to the effect of thermal nonequilibrium

Experimental Study on the Influence of Foam Porosity and Pore Size on the Melting of Phase Change Materials

Experimental study was carried out to study the phase change heat transfer within a composite of phase change material (PCM) infiltrated high thermal conductivity foam. An experimental setup was built to measure the temperature profiles and capture the melting evolution of the PCM inside aluminum foams. Aluminum foams were used as the porous material, and low melting temperature paraffin wax was used as the PCM. It was observed from the results that the system parameters of the wax/foam composite had a significant influence on its heat transfer behavior. By using higher porosity aluminum foam, the steady-state temperature was reached faster as compared to the foams with lower porosity. Similarly for the bigger pore size foams the steady state was attained faster as compared to the smaller pore size foams. This was due to the greater effect of convection in both the higher porosity and bigger pore size foams. However, for the lower porosity foams the heater temperature was comparatively lower than the higher porosity foams due to greater heat conduction through the foam material. Therefore, an optimal value should be selected for the foam porosity and pore size such that the effects of both conduction and convection heat transfers can be completely utilized to have a greater and improved thermal performance for the wax/aluminum foam composite