A functionalized surfactant, GME-N-C 10 containing a CdC double bond, was synthesized to modify clays such as montmorillonite (MMT) and mica for the preparation of organic-inorganic composite resins via radical photoinduced polymerization. As revealed by X-ray diffraction (XRD) analysis of the organophilic samples, the synthesized surfactant was successfully intercalated into the layers of clay by its full molecular length and such an intercalation generated a paraffin-like structure in the modified clays. By forming the C-C bonds between surfactants and oligomers/monomers during subsequent radical photoinduced polymerization, the hybrid comprising organophilic clay/oligomers/monomers became an intercalated nanocomposite resin. The thickness of the dispersed lamellae was less than 100 nm, as revealed by transmission electron microscopy (TEM). For the composite sample containing 5.0 wt.% of organophilic clay, the decomposition temperatures raised at least 15 °C; the transmittance detected by UV-visible spectrometer showed a less than 15% loss in the visible light region but a satisfactory transparency was still retained, and the degree of moisture absorption decreased from 3.4% to about 1% due to dispersive organophilic clay in the polymer matrix.
This work prepared the highly transparent photo-curable co-polyacrylate/silica nanocomposites by using sol-gel process. The FTIR and 13 C NMR analyses indicated that during the sol-gel process, the hybrid precursors transform into composites containing nanometer-scale silica particles and crosslinked esters/anhydrides. Transmission electron microscopy (TEM) revealed that the silica particles within the average size of 11.5 nm uniformly distributed in the nanocomposite specimen containing about 10 wt % of Si. The nanocomposite specimens exhibited satisfactory thermal stability that they had 5% weight loss decomposition temperatures higher than 1508C and coefficient of thermal expansion (CTE) less than 35 ppm/8C. Analysis via derivative thermogravimetry (DTG) indicated that the crosslinked esters/anhydrides might influence the thermal stability of nanocomposite samples. The UV-visible spectroscopy indicated that the nanocomposite resins possess transmittance higher than 80% in visible light region. Permeability test revealed a higher moisture permeation resistance for nanocomposite samples, which indicated that the implantation of nano-scale silica particles in polymer matrix forms effective barrier to moisture penetration. Adhesion test of nanocomposite samples on glass substrate showed at least twofold improvement of adhesion strength compared with oligomer. This evidenced that the silica and the hydrophilic segments in nanocomposite resins might form interchains hydrogen bonds with the À ÀOH groups on the surface of glass so the substantial enhancement of adhesion strength could be achieved.
Electrical properties of UV‐curable co‐polyacrylate/silica nanocomposite resins prepared via sol‐gel process for device encapsulation were investigated. It was found that, by appropriate UV curing process and the formation of nanoscale silica particles finely dispersed in the resin matrix, the leakage current density of the nanocomposite resin films decreases from 235 to 1.3 nA · cm−2 at the applied electrical field of 10 kV · cm−1. The silica nanoparticles also restricted the motions of polar functional groups in organic matrix that the nanocomposite films with satisfactory dielectric properties [dielectric constant (ε) = 3.93 and tangent loss (tanδ = 0.0472) could be obtained. Chemical structure analyses revealed that excessive UV curing results in photooxidation and/or photodegradation in resin samples, leading to the polar groups and ionic/radical segments in organic matrix as well as the SiOSi structure in the vicinity of silica nanoparticles. These organic/inorganic functional groups generated more permeation paths for charge carrier migration and hence deteriorated the electrical properties of the nanocomposite samples. Though post‐baking treatment at 80 °C for 1 h followed by UV curing improved the rigidity of the resin sample, it brought the polar functional groups closer to each other and similarly degraded electrical properties of the nanocomposite resins.magnified image
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