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Abstract
A new “in situ” sol–gel synthesis procedure was exploited to produce silica/epoxy nanocomposites with 6 wt.% maximum silica content. 3-Aminopropyltriethoxysilane (APTS) was used as a coupling agent. The experimental results (fourier-transform infrared spectroscopy, FTIR, small-angle X-ray scattering, SAXS, transmission electron microscopy, TEM, nuclear magnetic resonance, NMR, and dynamic mechanical analysis, DMA) support that the structure consists of nanosized silica particles (maximum 1.25 nm in size) embedded in a hybrid co-continuous network. A post cure non-isothermal heating from 15 to 100 °C (beyond the Tg of the neat epoxy) caused Tg and storage modulus to increase. The fire behavior, that, owing to severe regulations (i.e., in aerospace engineering), often prevents composites applications, was also studied. The formed silica domains prevented melt dripping phenomena during vertical flame spread tests. Cone calorimetry tests showed a remarkable decrease of the heat release rate (HRR) for all the hybrid systems with respect to the neat cured resin, even at very low silica loadings (i.e., 2 wt.%). This decrease was much more pronounced for the hybrid structures that were not subjected to the post cure thermal treatment. The use of multiple structural investigation techniques allowed to choose among multiple hypothesis and conclude that nanoparticles clustering is the main reason of the effects of the post curing treatments.SAXS of the samples before (EPO) and after (EPO_t) post cure thermal treatment in the glass transformation range. Effect of the post cure on the glass transformation temperature (Tg) and heat release rate (HRR) Photos of samples EPO and EPO 2%Si after vertical flame spread tests
Highlights
It is well-known that polymeric materials cannot be used for high-performance applications because of their limited properties
In the presence of silica, a remarkable evolution of the IR absorption bands in the frequency range between 1050 and 1150 cm−1 is observed. The absorption in this frequency range keeps on increasing in the hybrid samples: this finding can be ascribed to the presence of a progressively higher silica phase amount, proving its formation from the APTS and TEOS added to the batch through the following well-known reactions:
nuclear magnetic resonance (NMR) results suggest that the second effect is predominant
Summary
It is well-known that polymeric materials cannot be used for high-performance applications because of their limited properties. This limitation can be overcome by using organic/inorganic composites. They require nano-level molecular design but are expected to have unique properties that are not the sum of those of the composite components: unprecedented materials may be created with the hybrid strategy [3]. Organic-inorganic hybrid perovskites (e.g., CH3NH3PbI3), with advantages of easy processing, tunable bandgaps, and superior charge-transfer properties, have emerged as a new class of revolutionary optoelectronic semiconductors promising for various applications [6]
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