In situ synthesis of epoxy nanocomposites with hierarchical surface-modified SiO2 clusters

Abstract

Polymer nanocomposites are often produced using in situ approaches where an inorganic filler (as the dispersed phase) is synthesized directly in an organic matrix. Such an approach generally leads to improved dispersion and reduced agglomeration of the filler material. Epoxy-based nanocomposites have demonstrated promising properties for application as high-voltage insulation materials. In this work, a sol-gel based method has been adapted to synthesize surface-functionalized SiO 2 in situ in epoxy. The synthesized SiO 2 moieties were dispersed in clusters of 10-80 nm, and formed chemical bonds with the epoxy monomers via a silane coupling agent. Raman spectra show the formation of four-membered D 1 rings, which may be part of a cage-like structure similar to that of polyhedral oligomeric silsesquioxanes (POSS). SAXS measurements indicate that the SiO 2 clusters consist of a hierarchical structure with an increasing fractal dimension with increasing SiO 2 content. The nanocomposites displayed improved thermal stability, while the glass transition behavior varied depending on the structure and content of the SiO 2 moieties. While the relative permittivity showed no significant changes from that of pure epoxy, the onset of the dielectric relaxation changed with the SiO 2 structure and content, similar to the behavior observed for the glass transition.

The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO2

“…The features specific for the nanocomposite spectrum are the presence of the O-Si-O rocking band around 450 cm −1 , the band at 940–970 cm −1 for the ethyl (-C 2 H 5 ) groups from unreacted precursors and coupling agents, and a broader band at 1080–1100 cm −1 assigned to the Si-O-Si and Si-O-C stretching [ 29 ]. A more detailed description of the progress of the in situ sol–gel reactions and formation of the inorganic domains is provided in our previous work [ 24 ].…”

“…An outline of the sol-gel procedure used in the in situ synthesis of SiO 2 functionalized with APTES in epoxy. [24].…”

“…The composites were prepared using the procedure outlined in our previous work [ 24 ] and is illustrated in Scheme 1 . DGEBA was heated to 80 °C in a round bottom flask mounted with a reflux condenser.…”

“…Therefore, the purpose of this study was to investigate if epoxy nanocomposites fabricated using the in situ route presents reduced permittivity and dielectric loss, compared to nanocomposites fabricated using more conventional ex situ methods as reported in the literature. In the present work, epoxy-SiO 2 nanocomposites were prepared based on a sol–gel route described in our previous study [ 24 ], using different synthesis conditions (pH, SCA amount, and type). The morphology and structure of the inorganic network and the resulting complex permittivity of the nanocomposites were characterized.…”

“…Changes in the glass transition for the epoxy-SiO 2 nanocomposites with varying filler content prepared using APTES (with APTES:DGEBA of 1:10 and 1:30) and GPTMS with different pH conditions, compared to that of pure epoxy (0 wt.% filler content). The error in the measurements is ±2 • C. The data for the pH 2 APTES samples were taken from[24].…”