Project description:Carbon nanotube (CNT) grafted glass fiber reinforced epoxy nanocomposites (GFRP) present a range of stiffnesses (MPa to GPa) and length scales (μm to nm) at the fiber-matrix interface. The contribution of functionalized CNT networks to the local and bulk polymer dynamics is studied here by using a combination of torsion dynamical mechanical thermal analysis (DMTA), positron annihilation lifetime spectroscopy (PALS), and neutron scattering (NS) measurements. DMTA measurements highlight a reduction in the storage modulus (G') in the rubbery region and an asymmetric broadening of the loss modulus (G″) peak in the α-transition region. NS measurements show a suppressed hydrogen mean-square displacement (MSD) in the presence of glass fibers but a higher hydrogen MSD after grafting functionalized CNTs onto fiber surfaces. PALS measurements show greater free volume characteristics in the presence of the functionalized CNT modified composites, supporting the view that these interface layers increase polymer mobility. While NS and DMTA are sensitive to different modes of chain dynamics, the localization of functionalized nanotubes at the fiber interface is found to affect the distribution of polymer relaxation modes without significantly altering the thermally activated relaxation processes.
Project description:Ordered mesoporous carbons (OMCs), obtained by nanocasting using ordered mesoporous silicas (OMSs) as hard templates, exhibit unique arrangements of ordered regular nanopore/nanowire mesostructures. Here, we used nanocasting combined with hot-pressing to prepare 10 wt% OMC/OMS/SiO2 ternary composites possessing various carbon mesostructure configurations of different dimensionalities (1D isolated CS41 carbon nanowires, 2D hexagonal CMK-3 carbon, and 3D cubic CMK-1 carbon). The electric/dielectric properties and electromagnetic interference (EMI) shielding efficiency (SE) of the composites were influenced by spatial configurations of carbon networks. The complex permittivity and the EMI SE of the composites in the X-band frequency range decreased for the carbon mesostructures in the following order: CMK-3-filled > CMK-1-filled > CS41-filled. Our study provides technical directions for designing and preparing high-performance EMI shielding materials. Our OMC-based silica composites can be used for EMI shielding, especially in high-temperature or corrosive environments, owing to the high stability of the OMC/OMS fillers and the SiO2 matrix. Related shielding mechanisms are also discussed.
Project description:High performance functional coatings, based on hybrid organic/inorganic materials, are being developed to combine the polymer flexibility and ease of processing with the mechanical properties and versatility of inorganic materials. By incorporating silica nanoparticles (SiNPs) in the polymeric matrices, it is possible to obtain hybrid polymer films with increased tensile strength and impact resistance, without decreasing the flexural properties of the polymer matrix. The SiNPs can further be used as carriers to impart other functionalities (optical, etc.) to the hybrid films. By using polymer-coated SiNPs, it is possible to reduce particle aggregation in the films and, thus, achieve more homogeneous distributions of the inorganic components and, therefore, better properties. On the other hand, by coating polymer particles with silica, one can create hierarchically structured materials, for example to obtain superhydrophobic coatings. In this review, we will cover the latest developments in films prepared from hybrid polymer/silica functional systems.
Project description:Flexible conductive films have good deformability and conductivity, and are expected to be used in flexible electronic devices. In this paper, four kinds of flexible conductive films were successfully prepared by compounding nano-sized metal (Ni, Cu, Au or AuCu alloy) particles to CNT surface and then dispersing to polydimethylsiloxane matrix. Experiment results show that the conductivity of these prepared films are almost two orders of magnitude higher than that of CNT/polydimethylsiloxane films with the same CNT loadings. A simulation model based on percolation network theory and Monte Carlo technology is introduced to study the influence of nanoparticles on the composite conductivity. Results confirmed that the introduction of nanoparticles effectively reduces the effective resistance of CNT and the tunnelling resistance at CNT junctions. The intrinsic conductivity and the length diameter ratio of CNT, the intrinsic conductivity, the size and the coverage ratio of nanoparticles are the core parameters affecting the conductivity of composite. Compared with CNT/polydimethylsiloxane films, the optimized theoretical conductivity of these nano-sized particles enhanced composites can be further improved.
Project description:To combat water scarcity in remote areas around the world, adsorption-based atmospheric water harvesting (AWH) has been proposed as a technology that can be used alongside existing water production capabilities. However, commonly used adsorbents either have low water adsorption loadings or are difficult to regenerate. In this work, we developed two novel hierarchical silica-salt composites that both exhibit high water adsorption loadings under dry and humid conditions. The total water vapor loading, kinetics, and heats of water adsorption for both silica-salt composites were investigated. As hierarchical silicas have tunable pores and large pore volumes, these materials serve as effective host matrixes for the hygroscopic salt LiCl. Our results suggest that hierarchical pores play a significant role in water adsorption: micropores and some smaller mesopores act as "storage" sites for hygroscopic salt, whereas larger mesopores and macropores increase the accessibility of water vapor into the silica. Using this mix of pores, we achieved greater than 0.4 g H2O/g composite at 10% RH and 27 °C. Additionally, we found that the salt-impregnated silica and bare silica had the same heat of adsorption: 80-90 kJ/mol. The results suggest that the H-bond interactions are similar for both systems and that the primary mechanism at play here is water cluster adsorption/desorption. Despite the similar energies, the LiCl-containing materials exhibited considerably slower kinetics than bare silica materials. Of equal importance to the adsorption capacity and kinetics of these composites is their mechanical stability. To assess their mechanical stability, high-energy ball milling of silica was conducted to create more uniform particle sizes. However, reduced particle sizes came at a cost─the BET surface areas and pore volumes were drastically decreased after more than 1 h of ball milling. Findings from this study suggest that short-term ball milling may be a viable large-scale option to reduce particle size in silica materials without sacrificing significant performance.
Project description:Liquid crystalline networks (LCNs) are a class of polymers, which are able to produce mechanical actuation in response to external stimuli. Recent creation of LCNs with exchangeable links (xLCNs) makes LCNs easy moldable. As the xLCNs need to be shaped at a high temperature, it is important to enhance their thermal and mechanical properties. In this paper, a series of xLCNs/SiO₂ composites containing 1%-7% SiO₂ nanoparitcles (SNP) were prepared and their thermal and mechanical properties were examined. The results show that xLCNs/SNP composites have lower liquid crystalline-isotropic phase transition temperature and higher decomposition temperature than pure LCN. The tensile strength and the elongation at break of xLCNs at high temperatures were also enhanced due to the addition of SNPs.
Project description:The remarkable mechanical properties of carbon nanotubes, such as high elastic modulus and tensile strength, make them the most ideal and promising reinforcements in substantially enhancing the mechanical properties of resulting polymer/carbon nanotube composites. It is acknowledged that the mechanical properties of the composites are significantly influenced by interfacial interactions between nanotubes and polymer matrices. The current challenge of the application of nanotubes in the composites is hence to determine the mechanical properties of the interfacial region, which is critical for improving and manufacturing the nanocomposites. In this work, a new method for evaluating the elastic properties of the interfacial region is developed by examining the fracture behavior of carbon nanotube reinforced poly (methyl methacrylate) (PMMA) matrix composites under tension using molecular dynamics simulations. The effects of the aspect ratio of carbon nanotube reinforcements on the elastic properties, i.e. Young's modulus and yield strength, of the interfacial region and the nanotube/polymer composites are investigated. The feasibility of a three-phase micromechanical model in predicting the elastic properties of the nanocomposites is also developed based on the understanding of the interfacial region.
Project description:Silica nanotubes can serve as high aspect ratio templates for the deposition of inorganic nanoparticles to form novel hybrids. However, the nature of the interfacial binding is still an unresolved challenge when considered at the atomic level. In this work, novel nanocomposites have been successfully fabricated by the controlled nucleation and assembly of Sb₂S₃ nanoparticles on the surface of mercaptopropyl-functionalized silica/polymer hybrid nanotubes (HNTs). The Sb₂S₃ nanoparticles were strongly attached to the HNTs surface by interactions between the pendent thiol groups and inorganic sulfur atoms. Detailed analysis of the geometric and electronic structure using first-principle density functional theory demonstrates charge transfer from the nanoparticles to the underlying HNTs at the Sb₂S₃/HNTs interfaces. Formation of a packed array of Sb₂S₃ nanoparticles on the HNTs results in mixing of the electronic states of the components, and is mediated by the mercaptopropyl bridges between Sb₂S₃ and the outer layer of the HNTs.
Project description:Silica aerogels are a class of materials that can be tailored in terms of their final properties and surface chemistry. They can be synthesized with specific features to be used as adsorbents, resulting in improved performance for wastewater pollutants' removal. The purpose of this research was to investigate the effect of amino functionalization and the addition of carbon nanostructures to silica aerogels made from methyltrimethoxysilane (MTMS) on their removal capacities for various contaminants in aqueous solutions. The MTMS-based aerogels successfully removed various organic compounds and drugs, achieving adsorption capacities of 170 mg⋅g-1 for toluene and 200 mg⋅g-1 for xylene. For initial concentrations up to 50 mg⋅L-1, removals greater than 71% were obtained for amoxicillin, and superior to 96% for naproxen. The addition of a co-precursor containing amine groups and/or carbon nanomaterials was proven to be a valuable tool in the development of new adsorbents by altering the aerogels' properties and enhancing their adsorption capacities. Therefore, this work demonstrates the potential of these materials as an alternative to industrial sorbents due to their high and fast removal efficiency, less than 60 min for the organic compounds, towards different types of pollutants.
Project description:The method of measuring electrical volume resistivity in different directions was applied to characterize the filler orientation in melt mixed polymer composites containing different carbon fillers. For this purpose, various kinds of fillers with different geometries and aspect ratios were selected, namely carbon black (CB), graphite (G) and expanded graphite (EG), branched multiwalled carbon nanotubes (b-MWCNTs), non-branched multiwalled carbon nanotubes (MWCNTs), and single-walled carbon nanotubes (SWCNTs). As it is well known that the shaping process also plays an important role in the achieved electrical properties, this study compares results for compression molded plates with random filler orientations in the plane as well as extruded films, which have, moreover, conductivity differences between extrusion direction and perpendicular to the plane. Additionally, the polymer matrix type (poly (vinylidene fluoride) (PVDF), acrylonitrile butadiene styrene (ABS), polyamide 6 (PA6)) and filler concentration were varied. For the electrical measurements, a device able to measure the electrical conductivity in two directions was developed and constructed. The filler orientation was analyzed using the ratio σin/th calculated as in-plane conductivity σin-plane (σin) divided by through-plane conductivity σthrough-plane (σth). The ratio σin/th is expected to increase with more pronounced filler orientation in the processing direction. In the extruded films, alignment within the plane was assigned by dividing the in-plane conductivity in the extrusion direction (x) by the in-plane conductivity perpendicular to the extrusion direction (y). The conductivity ratios depend on filler type and concentration and are higher the higher the filler aspect ratio and the closer the filler content is to the percolation concentration.