No abstract

We report the synthesis of controlled sized Urea-formaldehyde (UF) microcapsules containing an epoxy healing agent via in situ emulsification polymerization for the study of self-healing epoxy systems. Scanning Electron Microscopy (SEM) confirmed that the capsules possessed rough external surface which enhanced mechanical interlocking. Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy were employed so as to determine the capsules thermal stability and decompositions and

The development of nanoscale reinforcements, which can tailor the interfacial strength and impart multiple functionalities on carbon fiber reinforced polymer (CFRP) composites, remains a challenge for their largescale adoption in diverse applications ranging from aerospace to transportation and construction industries. In this work radially aligned graphene nanoflakes (GNFs), grown directly on carbon fibers (CFs) via a simple one-step microwave plasma enhanced chemical vapor deposition method, without any catalyst, were used as a novel nano-reinforcement interface. A remarkable 28% enhancement in the tensile strength of the hybrid fibers was observed via singlefiber tensile strength tests, whereas the interfacial shear strength (IFSS) increased by 101.5%. Our results demonstrate that GNFs not only improve the interfacial strength between the GNFs and the epoxy resin but also enhance the in-plane mechanical strength of the CFsa well-known problem encountered with the direct growth of carbon nanotubes on CFs. In addition, GNFs provided embedded functionality via increased electrical conductivity (60.5% improvement for yarns and 16% for single fiber) and electrochemical capacitance (157% for yarns). This work indicates the potential of GNFs as an interphase for the simplified and costeffective production of stronger multifunctional CFRP composite materials.

Graphene has outstanding properties that make it an auspicious material for many applications. This work presents the production of graphene oxide (GO) via the Langmuir-Blodgett process and the subsequent restoration of single layer graphene flakes (SLGF) via the chemical reduction, and thermal annealing of the GO. Scanning electron microscopy (SEM) and optical images were used to evaluate the morphology and surface coverage of the substrate with GO flakes. Through this technique, smooth dispersion, controllable development, and population of the GO single flakes on the Si substrate without size limitation have been achieved. The height distribution of the GO was monitored after each processing step by AFM measurements. Additionally, the effects of each process on the structure of the samples was systematically studied via 2D Laser Raman spectroscopy (LRS) mapping. The determination of the layer number on each graphene flake was accomplished by monitoring the observed Raman shifts as a function of the position and confirmed via AFM measurements. The spectroscopic analysis of the single flakes was performed in order to study their topography and identify their quality as a function of the processing steps. Via the topographic 2D analysis of both the first-and second-order vibrational modes as a function of the position on the crystal, the degree of graphitization and/or the presence of defects, as well as the presence of internal stresses were mapped. Such a systematic determination of the effects of reduction and annealing on the structure of single layer graphene from reduced GO produced via the Langmuir-Blodgett process is reported for the first time in literature.

This experimental study is associated with the modification of glass fibers with efficient, organic, functional, thermoelectrically enabled coatings. The thermoelectric (TE) behavior of the coated glass fiber tows with either inherent p semiconductor type single wall carbon nanotubes (SWCNTs) or the n-type molecular doped SWCNTs were examined within epoxy resin matrix in detail. The corresponding morphological, thermogravimetric, spectroscopic, and thermoelectric measurements were assessed in order to characterize the produced functional interphases. For the p-type model composites, the Seebeck coefficient was +16.2 μV/K which corresponds to a power factor of 0.02 μW/m∙K2 and for the n-type −28.4 μV/K which corresponds to power factor of 0.12 μW/m∙K2. The p–n junction between the model composites allowed for the fabrication of a single pair thermoelectric element generator (TEG) demonstrator. Furthermore, the stress transfer at the interphase of the coated glass fibers was studied by tow pull-out tests. The reference glass fiber tows presented the highest interfacial shear stress (IFSS) of 42.8 MPa in comparison to the p- and n-type SWCNT coated GF model composites that exhibited reduced IFSS values by 10.1% and 28.1%, respectively.