Ru-Jong Jeng

Preparation and thermal properties of epoxy-silica nanocomposites from nanoscale colloidal silica

Epoxy-silica nanocomposites were obtained from directly blending diglycidylether of bisphenol-A and nanoscale colloidal silica and then curing with 4,4-diaminodiphenylmethane. The epoxy-silica nanocompoites showed good transparency and miscibility observed with AFM, SEM, and TEM. The thermal stability of the epoxy resins was improved with the incorporation of the colloidal silica. However, a depression on the glass transition temperature of the resins was observed, owing to the plasticizing effect of the colloidal silica. Moreover, the nanoscale colloidal silica did not show effectively synergistic effect on char formation and flame retardance with phosphorus.

Phosphorus-containing epoxy for flame retardant. I. Synthesis, thermal, and flame-retardant properties

A new phosphorus-containing oxirane, bis-(3-glycidyloxy)phenylphosphine oxide (BGPPO), was synthesized. Further curing BGPPO with diamine curing agents, dicyanodiamide (DICY), 4,4′-diaminodiphenylmethane (DDM), and 4,4′-diaminodiphenylsulfone (DDS), respectively, resulted in several phosphorylated epoxy resins. Compared with Epon 828, Eponex 1015, and DER 732, BGPPO showed relatively high reactivity toward diamine agents via DSC studies. Furthermore, the reactivity of the three curing agents toward BGPPO were found to be in the order of DDM > DICY > DDS. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorylated resins showed lower weight loss temperatures and higher char yields than did the Epon 828-based resins. The high char yields as well as high limited oxygen index (LOI) values of the BGPPO-based resins confirmed the effectiveness of phosphorus-containing epoxy resins as flame retardants.

Microstructural and morphological characteristics of PS–SiO2 nanocomposites

Abstract A series of organic–inorganic hybrid materials have been prepared by copolymerizing styrene and alkoxysilane-methacrylate via the sol–gel process. The alkoxysilane-containing copolymer precursors were synthesized by free-radical copolymerization of styrene with an alkoxysilane-containing monomer, methacrylic acid 3-(trimethoxysilyl)propyl ester (MAMSE), at several feeds. The copolymer precursors were then hydrolyzed and condensed to generate PS–SiO 2 hybrid sol–gel materials. The hybrid copolymers possess excellent optical transparency and a nanoscale microphase separation. The copolymer precursors and their hybrid copolymers were characterized by FT-IR spectra, 1 H NMR spectra, DSC, and TGA thermograms. Chemical structural effect on the morphology and thermal properties was investigated with SEM, mapping photographs, and high-resolution solid state 13 C and 29 Si NMR spectra. It was found that compatibility between copolymer and silica mainly comes from incorporating the polymer with silica covalently. Moreover, MAMSE could be hydrolyzed to methacrylic acid and ester-interchanged to silyl methacrylate during heat treatment. This also enhances the compatibility between the copolymer and silica. The thermal properties of the PS–SiO 2 hybrid copolymers are improved as silica content increase. However, the presence of silyl ester groups, which were formed during heat treatment, would reduce the thermal stability of the hybrid copolymers.

Flame retardant epoxy polymers based on all phosphorus-containing components

A phosphorus-containing epoxy resin, bis(3-t-butyl-4-glycidyloxyphenyl-2,4-di-t-butylphenyl)resorcinol diphosphate, was synthesized and subsequently cured with non-phosphorus containing amines, and/or novel phosphorus-containing aromatic or polyoxyalkylene amines. Chemical structures of these materials were characterized with FTIR, NMR, elemental analysis, and amine titration. The introduction of soft –P–O– linkage, polyoxyalkyene, or hard aromatic group into the backbones of the synthesized phosphorus-containing amines provides epoxy polymers with high phosphorus contents and tailored flexibility. Thermal analysis of differential scanning calorimeter and thermal gravimetric analysis (TGA) reveals that these resulted epoxy polymers possess moderate Tgs and thermal stability. Furthermore, high char yields in TGA analysis and high limited oxygen index values indicate that these phosphorus-containing epoxy polymers possess excellent flame retardant properties.

Synthesis and flame-retardant properties of phosphorus-containing polymers based on poly(4-hydroxystyrene)

Phosphorus-containing polystyrene was obtained through incorporating phosphate groups onto poly(4-hydroxystyrene). This was achieved by esterification with diethylchlorophosphate. The phosphorylation was confirmed by IR, 1H-NMR, and 31P-NMR analysis. By varying the feeding ratios of the reactants, the phosphorus content in the polymers could be successfully tailored and gave values of 12.8 to 4.9% by weight. This was further corroborated by elemental analysis. Thermal characteristics and temporal stability of the phosphorylated polymers were evaluated by DSC and TGA. High char yields (64% by weight) and LOI values of 41 were found for these polymers. Such properties make these polymers useful in flame retardants.

Polymers for Electro‐Optical Modulation

Second‐order nonlinear optical (NLO) properties of polymeric materials have been attracting a lot of attention, especially for such potential applications as fast waveguides electrooptic (EO) modulation and frequency‐doubling devices. For these photonic applications, the performance of the NLO materials has to be optimized. This requires not only a fundamental knowledge of inter‐relationship between their chemical and NLO properties, but new technologies competitive or superior to existing ones as well. This review focuses on the synthesis of NLO polymers including chromophore design, and the comparison among comprehensive EO polymer systems. Moreover, characterization and device fabrication of electro‐optical polymer planar waveguides are also reported in this review.

Single-Layered Graphene Oxide Nanosheet/Polyaniline Hybrids Fabricated Through Direct Molecular Exfoliation

In this study, we used direct molecular exfoliation for the rapid, facile, large-scale fabrication of single-layered graphene oxide nanosheets (GOSs). Using macromolecular polyaniline (PANI) as a layered space enlarger, we readily and rapidly synthesized individual GOSs at room temperature through the in situ polymerization of aniline on the 2D GOS platform. The chemically modified GOS platelets formed unique 2D-layered GOS/PANI hybrids, with the PANI nanorods embedded between the GO interlayers and extended over the GO surface. X-ray diffraction revealed that intergallery expansion occurred in the GO basal spacing after the PANI nanorods had anchored and grown onto the surface of the GO layer. Transparent folding GOSs were, therefore, observed in transmission electron microscopy images. GOS/PANI nanohybrids possessing high conductivities and large work functions have the potential for application as electrode materials in optoelectronic devices. Our dispersion/exfoliation methodology is a facile means of preparing individual GOS platelets with high throughput, potentially expanding the applicability of nanographene oxide materials.

High-performance and high-durability perovskite photovoltaic devices prepared using ethylammonium iodide as an additive

In this study, we determined that the film morphologies, crystallinities, and optical properties of CH3NH3PbI3−xClx perovskite (PVSK) layers can be manipulated by incorporating a small amount of ethylammonium iodide (EAI) into the perovskite precursor solution. For our EAI-derived films, we observed higher absorbances at higher wavelengths and higher degrees of crystallinity, both of which were associated with the higher surface coverage of the PVSK films. The optimized power conversion efficiency (PCE) improved from 9.4 ± 0.76 to 10.2 ± 0.58% after the addition of 0.5 vol% of EAI. Devices based on EAI-containing PVSK exhibited extremely high stability, retaining approximately 80% of their PCEs (T80) under accelerated heating (65 °C) in a dark N2-filled glove box for over 360 h. In contrast, the corresponding normal device was relatively sensitive to this temperature, with a T80 value of only 45 h. The improved device performance (PCE, stability) arose as a result of the presence of EAI suppressing the crystallization of CH3NH3PbI3−xClx.

Highly concentrated MoS2 nanosheets in water achieved by thioglycolic acid as stabilizer and used as biomarkers

In this work, we reported the synthesis of water soluble MoS2 quantum dots from the monolayer nanosheets of MoS2, using thioglycolic acid (TGA) with a sonication method. The gaps between the MoS2 layers were enlarged by the stirring process. Meanwhile TGA molecules strongly binding to the defect sites of MoS2 would reduce the van der Waals force between the MoS2 layers through sonication. This led to the improved dispersion of MoS2 monolayers in water. The addition of TGA molecules not only exfoliated the bulk of MoS2, but also modified the surface of MoS2 with carboxylic acid groups. As a result, highly concentrated MoS2 nanosheets were produced in water. Subsequently, heavy metal-free MoS2 quantum dots with sustained fluorescence emission, which were fabricated from hydrothermal treatment of MoS2 monolayers, can be utilized as cell biomarkers.

Synthesis and macroscopic second-order nonlinear optical properties of poly(ether imide)s containing a novel two-dimensional carbazole chromophore with nitro acceptors

Taking advantage of the multifunctional characteristics of carbazole along with rational molecular design, a two-dimensional carbazole chromophore with strong nitro acceptors was synthesized by a facile synthetic route. A first molecular hyperpolarizability of 163 × 10−30 esu was acquired through solvatochromic methods. By doping of the chromophores into an organosoluble poly(ether imide), a series of guest–host NLO polymers were acquired. A high doping level up to 20 wt% was obtained without observing aggregation of NLO chromophores. The compatibility between chromophore and poly(ether imide) was also investigated by SEM and extraction experiments. In terms of compatibility, the molecular weight distribution of the polymer plays an important role. The second harmonic coefficients (d33) for the NLO-active poly(ether imide)s range from 7 to 23 pm V−1 depending on the doping level. The effect of two-dimensional structure on the NLO temporal stability was investigated by tracing the second harmonic coefficient as a function of time. Moreover, the relaxation behavior of the NLO systems was further examined by dielectric analysis. Large rotational cone volumes give the two-dimensional chromophore excellent orientational stability when the temperature approaches the glass transition temperature observed from DEA.