Development of novel coatable compatibilized polyimide-modified silica nanocomposites

A series of novel coatable polyimide silica (PI-SiO2) nanocomposites have been synthesized. A new PI matrix, containing pendant hydroxyl groups, was prepared reacting diamine monomers (4,4'-diamino-4"- hydroxytriphenylmethane, and 4,4'- oxydianiline) and pyromellitic dianhydride (PMDA). Whereas, silica reinforcement was generated using TEOS. A coupling oligomeric species 2,6-bis(3-(triethoxysilyl)propyl)pyrrolo[3,4- f]isoindole-1,3,5,7(2H,6H)-tetraone (APA) was used to furnish silica nanoparticles with imide linkages and hydroxyl groups. As these groups are already present in PI matrix, so their presence in nanoparticles brought structural similarity, and hence enhanced phase connectivity among two phases. The resulting PI-SiO2 hybrids, with improved interfacial interactions through hydrogen bonding and like-like chemical interactions, displayed much enhanced morphological, thermomechanical, and thermal properties. The properties of resulting hybrids were studied by various advanced techniques and compared with PI-SiO2 hybrid system which was prepared from same polyimide and unmodified silica network.© Springer Science+Business Media Dordrecht 2014.

A new approach to determine rheological percolation of carbon nanotubes in microstructured polymer matrices

We demonstrate the rheological percolation of carbon nanotubes (CNTs) in microstructured polymer matrices. Polymer/CNT composites are fabricated from polycarbonates with different molecular weights to diversify the microstructures, which vary with the polymer radius of gyration and entanglements. We propose a model for the dispersion of CNTs in polymer matrices, which explains the electrical and rheological properties. The percolation theory represented by a power-law relation cannot account for the rheological percolation of CNTs in this work. Therefore, we investigate the crossover points to provide a quantitative indication of the rheological percolation threshold of nanofillers in polymer matrices. For the first time, the rheological percolation threshold is determined experimentally with this definition. The effects of molecular weight and shear viscosity of the medium on the percolation of CNTs are demonstrated separately. © 2013 Elsevier Ltd. All rights reserved.

Preferential Positioning of gamma-Ray Treated Multi-Walled Carbon Nanotubes in Polyamide 6,6/Poly(p-phenylene ether) Blends

Morphological characteristics and electrical conductivity of polyamide 6,6/poly(p-phenylene ether)/multi-walled carbon nanotube (PA66/PPE/MWCNT) ternary nanocomposites were investigated. The MWCNTs were modified by 60Co gamma ray (γ-ray) irradiation under a dry condition and O2 atmosphere, which introduces oxygen-containing functional groups on the surfaces of the MWCNTs and thereby provides better compatibility with the hydrophilic PA66 phase. It was observed that the MWCNTs are preferentially positioned in the continuous PA66 matrix, whereas PPE domains are almost free of MWCNTs. Since PA66 consists of a continuous phase and the MWCNTs are preferentially positioned in the PA66 phase, electrical conductivity of PA66/PPE/MWCNT ternary composites is higher than that of PA66/MWCNT binary composites at the same MWCNT content. It was observed that raising the processing temperature and increasing the mixing time were effective means of improving the electrical conductivity of the composites, via enhancement of MWCNT dispersion. [Figure not available: see fulltext.] © 2013 The Polymer Society of Korea and Springer Sciene+Business Media Dordrecht.