Jifang Fu

Highly populated and nearly monodispersed nanosilica particles in an organic medium and their epoxy nanocomposites.

An organic aminopropyl-functionalized nanosilica sol was synthesized in the presence of ethyl silicate, γ-(aminopropyl)triethoxysilane (KH550), and N,N-dimethylformamide (DMF) via a sol-gel technique and then used to prepare epoxy nanocomposites. Structure and morphology analyses of the obtained aminopropyl-functionalized nanosilicas were observed by dynamic light scattering (DLS), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). TEM and DLS showed that modified nanosilicas with an average diameter of 30 nm dispersed homogeneously in DMF. The effects of the aminopropyl-functionalized nanosilica particles on the flexural modulus, impact strength, glass transition temperature (Tg), and bulk resistivity (ρv) of the epoxy nanocomposites were investigated. The toughening mechanisms and microstructures were determined in terms of the impact fracture surface morphology using scanning electron microscopy.

Effect of aminopropylisobutyl polyhedral oligomeric silsesquioxane functionalized graphene on the thermal conductivity and electrical insulation properties of epoxy composites

In order to obtain homogeneous dispersion and strong interfacial interaction in epoxy nanocomposites, an effective approach is proposed to prepare aminopropylisobutyl polyhedral oligomeric silsesquioxane (ApPOSS) covalently grafted graphene (ApPOSS–graphene) enhancement epoxy (EP) hybrids with high thermal conductivity and electrical insulating property. The chemically converted ApPOSS–graphene 2D sheet with amine groups and rigid Si–O–Si cages is a versatile starting platform to prepare nanohybrids, which conduce to uniform dispersion and well compatibility of graphene in polymer matrix. Compared to pristine GO/EP, the interfacial interactions between ApPOSS–graphene and epoxy matrix through non-covalent and covalent bonds promote well dispersibility, compatibility and interfacial quality in composites, which contribute to improving thermal conductivity through forming effective heat conduct networks and decreasing thermal interfacial resistance. With the incorporation of only 0.25 and 0.5 wt% ApPOSS–graphene, the thermal conductivities of the ApPOSS–graphene/EP composites increase by 37.6% and 57.9% compared with neat EP, while maintaining high electrical resistivity. We believe that using ApPOSS chemically reducing and functionalized modifying GO may open a novel interface design strategy for extending applications of POSS and GO to fabricate high performance composites with high thermally conductive and electrically insulating properties.

Lanthanide complex-functionalized polyhedral oligomeric silsesquioxane with multicolor emission covered from 450 nm to 1700 nm

A new 2,2′-bipyridine-4,4′-dicarboxylic acid-functionalized polyhedral oligomeric silsesquioxane (named as bpdc-POSS) was successfully synthesized. Subsequently, six new Ln-bpdc-POSS (Ln = Eu, Tb, Sm, Nd, Yb, Er) hybrid materials covalently linked with lanthanide complexes were prepared, based on the bpdc-POSS material acting as a matrix. The Ln-bpdc-POSS hybrid materials retain the structure of POSS and size distribution approximately 50 nm, and display visible as well as near-infrared luminescence (covered from 450 to 1700 nm wavelength region) under UV/visible light excitation. The Ln-bpdc-POSS materials (Ln = Eu, Tb, Sm, Er, Nd, Yb) were characterized by using wide-angle X-ray powder diffraction, Fourier-transform infrared (FT-IR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), fluorescent spectroscopy and thermogravimetric analysis. The method offers advantages including the ease of synthesis and handling, as well as extending the use of POSS and expanding the field of luminescent inorganic–organic hybrid materials based on lanthanides.

Thermally Conductive Nanocomposites Based on Epoxy Modified with SiC and POSS

OAPS/SiC/EP, SiC/EP, A151-SiC/EP composites were prepared and their impact properties, flexural properties, thermal conductivity and insulation and thermal stability were investigated. The comparison of three different composites showed that OAPS/SiC/EP composites had best properties. The thermal conductivity of OAPS/SiC/EP composites increased with increasing filler content. The thermal conductivity of OAPS/SiC/EP composites with 20 wt% SiC was 0.34 W/mK and was 55% higher than that of unmodified EP.

Enhanced Thermal and Mechanical Properties of Epoxy Composites by Spherical Silica with Different Size

Spherical silica particles with mean diameter 350 nm, 500 nm and 1000 nm were used to modify o-cresol-novolac epoxy resin (ECN) at a ranging constant weight fraction from 0 to 20 wt%. The effects of particle size and fillers content on the impact strength, flexural modulus, dynamic mechanical analysis (DMA), coefficient of thermal expansion (CTE), dielectric properties and bulk resistivities of epoxy composites filled with spherical silica particles were investigated. The results revealed that the impact strength and flexural modulus showed significant improvements with the addition of spherical silica particles. The glass transition temperature (Tg) of composites was higher than that of pure epoxy. The maximum increment of Tg was 34 °C by the addition of 2 wt% D500. The CTE of the composites with different size silica exhibit much lower dimension changes than that of pure epoxy. The dielectric constant was decreased with the addition of spherical silica particles. However, the particle size exhibited weakly effect on the dielectric properties. The bulk resistivities of the composites have greatly improved compared to the pure epoxy and increase with decreasing the particle size.

Study on Electrical Properties and Morphology Behaviors of Epoxy Nanocomposites with Octa(3-aminopropyl)Polyhedral Oligomeric Silsesquioxane

In this work, octa(3-aminopropyl)polyhedral oligomeric silsesquioxane (Oap-POSS) [(NH2CH2CH2CH2)8Si8O12] was synthesized through hydrolytic condensation of (3-aminopropyl)triethoxysilane, and incorporated into epoxy resin (EP) cured with methyl hexahydrophthalic anhydride (MHHPA) to offer a series of novel POSS/EP nanocomposites. The microstructure, thermal stabilities, electric insulation and dielectric behaviors of the epoxy nanocomposites were studied. The results showed that the thermal stability and dielectric property of the POSS/EP increases with the incorporation of Oap-POSS into EP.