The processing of hierarchical nanocomposites

Fillers and Reinforcanents for Advanced Nanocomposites. http //dx.doi.oi 0.1016 978-0-08-100079-3.00009-0 Copyright 2015 Elsevier Ltd. All rights reserved. 

In this study, the effects of exfoliated GO on the processing characteristics of glass fabric composites fabricated by the RI process were investigated. The objective of this 

The original GO suspension was diluted to 1 mg/mL using ethanol. The mixtures were ultrasonicated in a bath for 30 min. The prepared GO suspension was mixed with epoxy resin under magnetic stirring. The epoxy mixture was then stirred at 100 °C to remove the solvents. After complete solvent removal, the epoxy mixture was allowed to cool down to room temperature. Then the epoxy mixture was placed in a vacuum chamber for approximately 10 min to remove any air bubbles. 

Rheological tests of epoxy resin were performed using a TA Instruments Discovery Hybrid Rheometer with a peltier plate fixture of 25-mm disposable parallel plates. Similar to DSC tests, batches of approximately 50 g of epoxy resin, with GO contents of 0,0.05,0.1, and 0.2 wt%, and the appropriate amount of hardener were mixed. Samples of approximately 2 mL of mixed resin samples were pipetted onto the rheometer bottom plate. Rheological tests were performed with a 0.5-mm plate gap at a constant shear rate of 2.5 s Temperature sweep tests were completed for the determination of temperature-dependent viscosity evolution and were performed on all samples from 25 to 95 °C. Isothermal rheology tests were conducted at 80 °C to determine the viscosity evolution with respect to time. This temperature was selected after investigating the dynamic DSC scans in which peak temperature was approximately 82 °C. 

Specimens were cut and flexural tests were conducted using a three-point bending rig mounted on an Instron 4505 universal testing machine (load cell capacity 5 kN). AU tests were performed under ASTM D7264. The crosshead speed was 1 mm/min with a support span-to-thickness ratio of 32 1. At least seven samples for each batch were tested for good reproducibility. Average data were accordingly reported with standard deviations. 

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Continuous mesoporous carbon thin films were fabricated by direct carbonization of sucrose-silica nanocomposite films and subsequent removal of the silica [236]. The mesoporous carbon film with uniform and interconnected pores had a surface area of 2603 mVg and a pore volume of 1.39 cmVg. Subsequently, nanoporous carbons with bimodal PSD centered at about 2 and 27 nm in diameter were prepared by using both the TEOS-derived silica network and the colloidal silica particles as templates [237]. Figure 2.33 illustrates the preparation pathway. The pore sizes of the carbon are determined by the sizes of the added silica particles and the silica network. As the colloidal silica particles are commercially available with different diameters (e.g., 20 to 500 nm), this dual template synthesis process provides an efficient route to preparing nanoporous carbons with a controllable hierarchical pore structure. 

The CNT/polymer nanocomposites can be fabricated by means of solution blending, in situ polymerization and melt compounding [33-39]. The properties of CNT /polymer nanocomposites are directly related to their hierarchical microstructures. The processing conditions and polymers selected dictate the morphology, structure, electrical and mechanical properties of CNT/polymer nanocomposites. In addition, exfoliation and homogeneous dispersion of CNTs in the polymer matrix also play important roles in electrical properties of the composites. The agglomeration of nanotubes is detrimental to the formation of a conductive path network through the matrix of percolative CNT/polymer nanocomposites. 

Figure 4.5 Bright-field TEM of the hierarchical composite structure (at the pm and nm length scales) of melt-processed PET/organo-MMT nanocomposites, (top) Melt-processed copolymer-PET/3 wt% Ci6H33-imidazolium MMT boxes indicate the region of the subsequent higher-magnification image [44]. (middle) Melt-processed homopolymer-PET/3 wt% CieHaa-imidazolium MMT [44]. (bottom) Melt-processed homopolymer-PET/3 wt% Ci6H33-quinolinium MMT [25]. 2010, 2006 Wiley, reproduced with permission.

As in the case of other material systems, the macroscopic properties of nanocomposites are driven by their micro-/nanoscopic structure. From an electrical insulation perspective, polyethylene (PE) and epoxy resins constitute two technologically important material systems, each of which embodies in very different ways, a great deal of structural complexity. In the case of PE, the constituent molecules are the result of the inherently statistical polymerisation process, which can ultimately result in the formation of a hierarchical morphology in which different molecular fractions become segregated to specific morphological locations. In an epoxy resin, the epoxy monomer chemistry, the hardener and the stoichiometry can all be varied, to affect the network structure that evolves. In the case of nanocomposites, another layer of structural hierarchy is then overlaid upon and interacts with the inherent characteristics of the host matrix. 

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