Weibing Xu

Polyvinyl chloride/ montmorillonite nanocomposites

Polyvinyl chloride (PVC)/organic-montmorillonite composites were prepared by melt intercalation. Their structures and properties were investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC) and mechanical testing. The results showed that PVC chains could be intercalated into the gallery of organically modified montmorillonite to form exfoliated PVC/organic-montmorillonite nanocomposites, and the glass transition temperatures of PVC/organic-montmorillonite composites were lower than that of neat PVC. However, the tensile strength, and both the Izod type and Charpy notched impact strengths of PVC/organic-montmorillonite nanocomposites were fitted with the linear expressions: t=535.07-6.39Tg, sI=378.76-4.59Tg and sC=276.29-3.59Tg, respectively.

PE/Org-MMT nanocomposites

The non-isothermal crystallization kinetics of polyethylene (PE), PE/organic-montmorillonite (Org-MMT) composites were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the non-isothermal crystallization process of these samples very well. The difference in the exponent n between PE and PE/Org-MMT nanocomposites, indicated that non-isothermal kinetic crystallization corresponded to tridimensional growth with heterogeneous nucleation. The values of half-time, Zc and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PE and PE/Org-MMT composites, but the crystallization rate of PE/Org-MMT composite was faster than that of PE at a given cooling rate. The method developed by Ozawa did not describe the non-isothermal crystallization process of PE very well. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The results showed that the activation energy of PE/Org-MMT was greatly larger than that of PE.

Tunable electroluminescence from polymer-passivated 3C-SiC quantum dot thin films

Strong room-temperature photoluminescence in the wavelength range of 400-540 nm is achieved from a thin film containing polymer encapsulated 3C-SiC quantum dots (QDs). The QD surface is completely passivated by the polymer so that the QD film possesses voltage-tunable electroluminescence. The electroluminescence spectrum blue-shifts from 490 to 460 nm when the applied voltage is increased from 5 to 10 V. The tunable electroluminescence is attributed to carrier recombination in the core quantum confinement states as a result of Pool-Frenkel emission. Owing to the environmental friendliness, nontoxicity, easy fabrication, and stability, the polymer passivated 3C-SiC QD thin films have promising applications.

Electronic states and photoluminescence of TiO2 nanotubes with adsorbed surface oxygen

The electronic states associated with enhanced photocatalytic activity of anodic anatase TiO2 nanotubes (NTs) annealed in N2 and O2 are investigated by photoluminescence (PL). The NTs annealed in N2 show a green peak related to oxygen vacancies and its position blueshifts with deceasing temperature, whereas those annealed in O2 show a double peak at 475–600 nm and the energy separation increases with decreasing temperature. Spectral analysis and density function theory calculation disclose that the double peak results from residual oxygen vacancies and oxygen atoms on the NT wall and the increased energy separation arises from the larger difference between the inner and outer NT stress at low temperature.

Blocked isocyanate silane modified Al2O3/polyamide 6 thermally conductive and electrical insulation composites with outstanding mechanical properties

The surface of alumina (Al2O3) particles was modified by a blocked isocyanate silane coupling agent, which was synthesized by using methylethyl ketoxime (MEKO) to block isocyanate-propyltriethoxy silane via nucleophilic reactions. For comparison, the surface of Al2O3 particles was also modified by propyltrimethoxy silane (KH-331). The thermally conductive and electrical insulating Al2O3/polyamide 6 composites were prepared by dispersing modified Al2O3 in polyamide 6 (PA6) using a twin-screw extruder. The X-ray photoelectron spectroscopy (XPS) results revealed that blocked isocyanate-propyltriethoxy silane and KH-331 were successfully attached to the surface of Al2O3 particles with chemical bonds. The blocked isocyanate silane modified Al2O3 were well dispersed in PA6 as revealed by scanning electron microscopy (SEM). When the Al2O3 content was 70 wt%, the tensile strength (85.2 MPa) and flexural strength (136.4 MPa) of blocked isocyanate silane modified Al2O3/PA6 composites were higher than those of KH-331 modified Al2O3/PA6 composites (52.5 MPa, 77.8 MPa), respectively. The thermal conductivity and impact strength of blocked isocyanate silane modified Al2O3/PA6 composites were also higher than that of KH-331 modified Al2O3/PA6 composites at the same content of Al2O3. The volume electrical resistivity of modified Al2O3/PA6 composites decreased with increasing Al2O3 content, but they still were good electrical insulating materials.

Direct Synthesis of P3Ht/Cds Nanocomposites with End-Functionalized P3Ht as the Template

In this article, we report a direct synthetic route to prepare P3HT/CdS nanocomposites with cadmium acetate dihydrate (Cd(OOCCH3)2.2H2O) used as the cadmium source, sulfur powder (S) as the sulfur source, dichlorobenzene (DCB) and dimethyl sulfoxide (DMSO) as cosolvents, phosphonic ester end-functionalized P3HT as a conjugated polymer template. The as-prepared P3HT/CdS nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, X-ray diffraction (XRD) patterns, transmission electron microscope (TEM), ultraviolet-visible (UV-vis) and photoluminescence (PL) spectra. The results showed that the size and distribution of CdS nanocrystals were not only temperature-dependent, but also greatly influenced by the S/Cd molar ratio. CdS nanocrystals were dispersed uniformly in the P3HT/CdS nanocomposites, which indicated that end-functionalized P3HT could be used as a template to prevent CdS from aggregating effectively. The occurrence of charge transfer at the P3HT/ CdS interface was evident from UV-vis absorption and PL studies, which indicated that ionic bonding between CdS nanocrystals and phosphonic ester end-functionalized P3HT can promote the transfer of charge in P3HT/ CdS nanocomposites. Therefore, it is a promising method to simplify the procedure for large-scale synthesis of organic-inorganic nanocomposites used in solar cells with high photoelectric conversion efficiency.

Formation mechanism of thermally expandable microspheres of PMMA encapsulating NaHCO3 and ethanol via thermally induced phase separation

Thermally expandable microspheres (TEMs), employing PMMA as the shell and NaHCO3/ethanol as the core, were prepared via thermally induced phase separation (TIPS). The addition of NaHCO3 improves the foaming properties of the TEMs. A mechanism for TEMs formation was proposed, comprising the following steps: (1) the separation of homogeneous polymer solutions into polymer-rich and polymer-poor phases upon cooling, where decreases in both interfacial tension and interfacial free energy (ΔG) facilitate sphere formation in a polymer-rich phase located in the polymer-poor phase; (2) the deposition of PMMA and shell formation at the interface, aided by the acute contact angle (θ) and positive spreading coefficient (S); (3) the constant deposition of PMMA shells from both the polymer-rich phase and polymer-poor phase upon cooling; and (4) the detachment of TEMs from each other facilitated by shear force from stirring. This mechanism was supported by calculations, and the effects of quench rates and stirring speeds.

A facile approach to the synthesis of CdSe/P3HT nanocomposites

In this article, we report a facile, direct synthesis route to prepare CdSe/P3HT nanocomposites with CdO used as cadmium source, Se powder as selenium source, liquid paraffin and oleic acid as solvents, P3HT as a conjugated polymer template. The effect of the reaction temperature as well as the Cd:Se molar ratio on the morphology and photovoltaic property of CdSe/P3HT nanocomposites was studied. The results show that the shape and the degree of aggregation of CdSe nanocrystals are not only temperature-dependent, but also heavily influenced by the Cd:Se ratio, changing from dot-shaped to tetrapod-shaped, and from homo-dispersed to seriously aggregative. The UV–vis absorption spectra of CdSe-P3HT show a broader range and higher intensity of absorption than that of pure P3HT. The improved PL quenching in PL spectra of CdSe-P3HT indicates charge transfer between CdSe nanocrystals and P3HT.

Polymer Composites with Enhanced Thermal Conductivity and Mechanical Properties for Geothermal Heat Pump Pipes

In this article, we report a robust strategy to prepare polymer composites with enhanced thermal conductivity and mechanical properties for geothermal heat pump pipes, in which high density polyethylene (HDPE) used as matrix, various inorganic fillers including zero-dimensional (0D) aluminium spherical particles (Al-SPs), one-dimensional (1D) carbon fibres (CF) and two-dimensional (2D) graphite platelets (GPs), used alone or blended as modifier. The as-prepared polymer composites are GPs/HDPE, GPs/CF/HDPE, GPs/Al-SPs/HDPE and GPs/CF/Al-SPs/HDPE. Thermal conductivity and mechanical properties of these polymer composites were characterised. The results indicate that of all these as-prepared polymer composites, GPs/CF/Al-SPs/HDPE composites are the only one which possesses preferable and comprehensive properties both in thermal conductivity and mechanical properties due to the synergistic effect of filler. The thermal conductivity, elongation at break and tensile strength of GPs/ CF/Al-SPs/HDPE composites prepared with GPs (9 wt%), CF (3 wt%) and Al-SPs (3 wt%) were 0.803 W m−1K−1, 70.6 % and 26.69 MPa, respectively, which could meet the commercial requirements of the geothermal heat pump pipes.

Water as Blowing Agent: Preparation of Environmental Thermally Expandable Microspheres via Inverse Suspension Polymerization

ABSTRACT Water-encapsulated environment-friendly core–shell thermally expandable microspheres (TEMs) were prepared via inverse suspension polymerization under atmospheric pressure. Acrylonitrile (AN), methyl methacrylic acid (MMA), and methacrylate (MA) were used as monomers, and water was used as the core material. The influences of dispersants, monomer feed ratio, and cross-linking agent on the TEMs were systematically investigated. The water could disperse well in the continuous oil phase employing both 6 g spand 80 and 0.2 g calcium stearate as dispersants. When the feed ratio of AN/MMA/MA was set at 1:2:2 and 1,4-butanediol dimethacrylate was used as cross-linking agent, TEMs possessed excellent properties. The properties of melamine resin foamed by TEMs-encapsulated water were better than that of n-octane and TEMs-encapsulated n-octane. GRAPHICAL ABSTRACT