Modeling and characterization of the mechanical and damping response of carbon nanotube nanocomposites

"Modeling and Characterization of the Mechanical and Damping Response of Carbon Nanotube Nanocomposites" ABSTRACT: Multifunctionality is a current trend in material design. The fast growing needs of industries are challenging the design of structures made of advanced lightweight composites that possess the capability of performing multiple functions. The superior mechanical properties of carbon nanotubes (CNTs) - besides the excellent electrical and thermal properties - make them ideal candidates to be used as reinforcement llers in composite materials. CNT nanocomposites, made of suitable polymeric matrices lled with carbon nanotubes, have shown enhanced mechanical and electrical features with an additional extraordinary feature, namely, a high structural damping capacity. The main objective of this work is to explore the mechanical and damping response of CNT nanocomposites, aiming at reaching a better understanding of the macroscopic behavior of the nanocomposite materials by taking into account their complex micro/nanostructural features. The practical goal is to effectively explore the potential exploitation of these nanostructured materials in demanding structural applications. In order to investigate and optimize not only the mechanical properties but also the damping capacity of CNT/polymer composites, a specic analytical model, based on the Eshelby and Mory-Tanaka approaches, is here presented. The proposed model is an effective tool for predicting nonlinear stress-strain curves, energy dissipation mechanisms and hysteresis of nanocomposite materials. A great deal of studies were conducted on the ability of CNT-reinforced materials to absorb vibrations and noise (damping capacity), analyzing the orientation, dispersion and aspect ratio of CNTs as main parameters that affect the mechanical and damping properties. As a step forward from the current state of the art, the present work suggests an innovative theoretical method to describe the macroscopic response of nanocomposites and explore energy dissipation mechanisms arising from the shear slippage of nanotubes within the hosting matrix. The major mechanism through which energy is dissipated, the stick-slip mechanism, can be properly treated by introducing a plastic eigenstrain in the CNT inclusions whose evolutive law is accordingly shaped after the physical phenomenology. A set of numerical tests are performed to estimate the elastic properties and the nonlinear response of nanocomposites, characterizing the hysteresis loops in the stress-strain curves. Parametric studies are conducted to investigate the in uence of the main constitutive parameters of the model on the mechanical response including the damping capacity. The numerical simulations revealed that the interfacial shear strength, the CNT volume fraction, the exponent of the evolution law for the plastic eigenstrain, as well as the strain amplitude, have a signicant effect on the hysteresis of CNT nanocomposites. Moreover, it is shown that an optimal combination of these micro-structural parameters can be achieved via differential evolutionary algorithms that allow to maximize the damping capacity, while preserving the high elastic properties of the nanostructured materials. Such approach further enables the calibration of the model and design the nanomaterial in order to provide an effective response according to the structural vibration control requirements and high mechanical performance goals. The validation of the effectiveness of the predictive computational tool, together with its theoretical framework, is also sought via an ad hoc experimental approach. The experimental campaign featuring mechanical tests on a variety of CNT nanocomposite materials was indeed a fundamental step towards the renement of the model and a reasonable tuning of the model parameters. In addition, a morphology investigation of the prepared CNT/polymer composites was a decisive step to dene the microstructural properties. The experimental activities highlighted and conrmed the relevance of several morphological aspects, such as the actual CNT aspect ratio variability within the nanocomposite, the CNT dispersion and agglomeration degree and the polymer matrix chemical structure, to mention but a few. Those results shed light to which nanocomposites constituents features can influence the macroscopic response of the material. The conducted experimental work aimed also at identifying and introducing parameters that can better enhance the nanocomposite mechanical and damping behavior, by investigating also aspects of the fabrication processes that can help improve the CNT dispersion or the CNT adhesion like, for instance, the CNT functionalization. These experimental findings allowed a final model update by overcoming the main limitations, generally present in the most common micromechanical theories for multi-phase materials, i.e., (i) the perfect nanoller dispersion and distribution in the surrounding matrix, and (ii) the perfect interfacial adhesion between the carbon nanotubes and polymer chains

A vector light sensor for 3D proximity applications: Designs, materials, and applications

In this thesis, a three-dimensional design of a vector light sensor for angular proximity detection applications is realized. 3D printed mesa pyramid designs, along with commercial photodiodes, were used as a prototype for the experimental verification of single-pixel and two-pixel systems. The operation principles, microfabrication details, and experimental verification of micro-sized mesa and CMOS-compatible inverse vector light pixels in silicon are presented, where p-n junctions are created on pyramid’s facets as photodiodes. The one-pixel system allows for angular estimations, providing spatial proximity of incident light in 2D and 3D. A two-pixel system was further demonstrated to have a wider-angle detection. Multilayered carbon nanotubes, graphene, and vanadium oxide thin films as well as carbon nanoparticles-based composites were studied along with cost effective deposition processes to incorporate these films onto 3D mesa structures. Combining such design and materials optimizations produces sensors with a unique design, simple fabrication process, and readout integrated circuits’ compatibility. Finally, an approach to utilize such sensors in smart energy system applications as solar trackers, for automated power generation optimizations, is explored. However, integration optimizations in complementary-Si PV solar modules were first required. In this multi-step approach, custom composite materials are utilized to significantly enhance the reliability in bifacial silicon PV solar modules. Thermal measurements and process optimizations in the development of imec’s novel interconnection technology in solar applications are discussed. The interconnection technology is used to improve solar modules’ performance and enhance the connectivity between modules’ cells and components. This essential precursor allows for the effective powering and consistent operations of standalone module-associated components, such as the solar tracker and Internet of Things sensing devices, typically used in remote monitoring of modules’ performance or smart energy systems. Such integrations and optimizations in the interconnection technology improve solar modules’ performance and reliability, while further reducing materials and production costs. Such advantages further promote solar (Si) PV as a continuously evolving renewable energy source that is compatible with new waves of smart city technology and systems

Experimental and Theoretical Analysis of Pressure Coupled Infusion Gyration for Fibre Production

In this work, we uncover the science of the combined application of external pressure, controlled infusion of polymer solution and gyration in the field of nanofiber preparation. This novel application takes gyration-based method into another new arena through enabling the mass production of exceedingly fine (few nanometres upwards) nanofibres in a single step. Polyethylene oxide (PEO) was used as a model polymer in the experimental study, which shows the use of this novel method to fabricate polymeric nanofibres and nanofibrous mats under different combinations of operating parameters, including working pressure, rotational speed, infusion rate and collection distance. The morphologies of the nanofibres were characterised using scanning electron microscopy, and the anisotropy of alignment of fibre was studied using two dimensional fast Fourier transform analysis. A correlation between the product morphology and the processing parameters is established. The response surface models of the experimental process were developed using the least squares fitting. A systematic description of the PCIG spinning was developed to help us obtain a clear understanding of the fibre formation process of this novel application. The input data we used are the conventional mean of fibre diameter measurements obtained from our experimental works. In this part, both linear and nonlinear fitting formats were applied, and the successes of the fitted models were mainly evaluated using Adjusted R2 and Akaike Information Criterion (AIC). The correlations and effects of individual parameters and their interactions were explicitly studied. The modelling results indicated the polymer concentration has the most significant impact on fibre diameters. A self-defined objective function was studied with the best-fitted model to optimise the experimental process for achieving the desired nanofibre diameters and narrow standard deviations. The experimental parameters were optimised by several algorithms, and the most favoured sets of parameters recommended by the non-linear interior point methods were further validated through a set of additional experiments. The results of validation indicated that pressure coupled infusion gyration offers a facile way for forming nanofibres and nanofibre assemblies, and the developed model has a good prediction power of experimental parameters that are possible to be useful for achieving the desirable PEO nanofibres

NASA Tech Briefs, April 2010

Topics covered include: Active and Passive Hybrid Sensor; Quick-Response Thermal Actuator for Use as a Heat Switch; System for Hydrogen Sensing; Method for Detecting Perlite Compaction in Large Cryogenic Tanks; Using Thin-Film Thermometers as Heaters in Thermal Control Applications; Directional Spherical Cherenkov Detector; AlGaN Ultraviolet Detectors for Dual-Band UV Detection; K-Band Traveling-Wave Tube Amplifier; Simplified Load-Following Control for a Fuel Cell System; Modified Phase-meter for a Heterodyne Laser Interferometer; Loosely Coupled GPS-Aided Inertial Navigation System for Range Safety; Sideband-Separating, Millimeter-Wave Heterodyne Receiver; Coaxial Propellant Injectors With Faceplate Annulus Control; Adaptable Diffraction Gratings With Wavefront Transformation; Optimizing a Laser Process for Making Carbon Nanotubes; Thermogravimetric Analysis of Single-Wall Carbon Nanotubes; Robotic Arm Comprising Two Bending Segments; Magnetostrictive Brake; Low-Friction, Low-Profile, High-Moment Two-Axis Joint; Foil Gas Thrust Bearings for High-Speed Turbomachinery; Miniature Multi-Axis Mechanism for Hand Controllers; Digitally Enhanced Heterodyne Interferometry; Focusing Light Beams To Improve Atomic-Vapor Optical Buffers; Landmark Detection in Orbital Images Using Salience Histograms; Efficient Bit-to-Symbol Likelihood Mappings; Capacity Maximizing Constellations; Natural-Language Parser for PBEM; Policy Process Editor for P(sup 3)BM Software; A Quality System Database; Trajectory Optimization: OTIS 4; and Computer Software Configuration Item-Specific Flight Software Image Transfer Script Generator

Engineering Hyaluronic Acid Carbon Nanotube Nanofibers: A Peripheral Nerve Interface To Electrically Stimulate Regeneration

Peripheral nerve injuries annually affect hundreds of thousands of people globally. Current treatments like the gold standard autograft and commercially available nerve guide conduits (NGC) are insufficient to repair long gap peripheral nerve injuries. NGCs can aid recovery but lack key microenvironment cues that promote nerve regeneration. We hypothesized that providing topographical, mechanical, and electrical guidance cues through a nanofibrous composite biopolymer would result in improved neuron growth metrics using an in vitro model. We embedded hydrophilic carbon nanotubes (CNT) within hyaluronic acid (HA) nanofibers by electrospinning. The aims of this study were (1) to define the topographical, nanomechanical, and electrochemical material properties of HA-CNT nanofibers and (2) to determine the electrical stimulus parameters required to elicit increased neurite outgrowth on our nanofibrous scaffold. Mechanical properties were evaluated under physiological conditions using nanofiber samples hydrated to equilibrium. Local elastic modulus was measured by fitting atomic force microscopy quantitative nanomechanical mapping data to the Sneddon model. The mean and standard error for Local Young\u27s modulus was 74.93±12.6 kPa for HA nanofibers and 174.85±31.9 kPa for HA-CNT nanofibers. The electrochemical characterization performed was electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Conductivity and charge storage capacity of HA-CNT nanofibers were significantly increased. EIS resulted in a decreased resistance to current flow by a factor of 1.7 at 20 Hz and 1.2 at 1kHz. CV revealed a 2.1-fold increase in specific capacitance (mF/cm2) of HA-CNT relative to HA nanofibers. Chick dorsal root ganglia neurons grown on HA or HA-CNT substrates for 24h were either unstimulated or stimulated at 20Hz for 30min or 60min using a charge balanced 150, 200, or 250mV/mm square wave. Neuron outgrowth after 72h was significantly longer on HA-CNT substrates electrically stimulated for 60min at all stimulus amplitudes versus all other groups (p \u3c 0.01). Significant effects of fiber type, time, and stimulus amplitude were also observed when measuring neuron viability. This study demonstrates the potential of combining electrical stimulation with material based repair strategies for neural regeneration. Further, the results contribute to defining the electrical stimulus parameters necessary for regeneration in the peripheral nerve environment. Incorporating well-dispersed hydrophilic CNTs in HA nanofibers significantly enhances neural regeneration following electrical stimulation in vitro. Future work encompasses characterizing glial responses to electrical stimulation including electrophysiological calcium imaging assays to elucidate the governing molecular mechanisms for both neuronal and glial behavior

Biomedical Engineering

Biomedical engineering is currently relatively wide scientific area which has been constantly bringing innovations with an objective to support and improve all areas of medicine such as therapy, diagnostics and rehabilitation. It holds a strong position also in natural and biological sciences. In the terms of application, biomedical engineering is present at almost all technical universities where some of them are targeted for the research and development in this area. The presented book brings chosen outputs and results of research and development tasks, often supported by important world or European framework programs or grant agencies. The knowledge and findings from the area of biomaterials, bioelectronics, bioinformatics, biomedical devices and tools or computer support in the processes of diagnostics and therapy are defined in a way that they bring both basic information to a reader and also specific outputs with a possible further use in research and development