All issues / Volume 6 (2012) / Issue 6 (June)
This is an editorial article. It has no abstract.
The theoretical description of electrical properties of polymer melts, filled with attractively interacting conductive particles, represents a great challenge. Such filler particles tend to build a network-like structure which is very fragile and can be easily broken in a shear flow with shear rates of about 1 s–1. In this study, measured shear-induced changes in electrical conductivity of polymer composites are described using a superposition approach, in which the filler particles are separated into a highly conductive percolating and low conductive non-percolating phases. The latter is represented by separated well-dispersed filler particles. It is assumed that these phases determine the effective electrical properties of composites through a type of mixing rule involving the phase volume fractions. The conductivity of the percolating phase is described with the help of classical percolation theory, while the conductivity of non-percolating phase is given by the matrix conductivity enhanced by the presence of separate filler particles. The percolation theory is coupled with a kinetic equation for a scalar structural parameter which describes the current state of filler network under particular flow conditions. The superposition approach is applied to transient shear experiments carried out on polycarbonate composites filled with multi-wall carbon nanotubes.
A new conjugated polymer with donor-acceptor architectures based on alternating 1,4-divinyl-2,5-dioctyloxybenzene and 5,8-(2,3-dipyridyl)-quinoxaline: Synthesis, characterization, and photoinduced charge transfer
S. J. Chen, Q. Y. Zhang, J. W. Gu, M. L. Ma, L. Zhang, J. Zhou, Y. Y. Zhou
Vol. 6., No.6., Pages 454-464, 2012
Vol. 6., No.6., Pages 454-464, 2012
A new conjugated polymer with donor-accepter architectures poly[1,4-dioctyloxyphenylene-2,5-diylethenylene-(2,3-dipyridine-2-ylquinoxaline-5,8-diyl)ethylene] (PPV-BD) was synthesized successfully, in which the electron-donating unit was alkoxy substituted phenyl ring, and the electron-accepting unit was a quinoxaline. The resulting polymer had a lower band-gap (1.98 eV) compared to poly[2-methoxy-5-(2-ethyl)hexoxy-phenylenevinylene] (MEH-PPV, 2.12 eV), and was characterized by infrared spectroscopy (IR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy and X-ray diffraction (XRD). Its photoinduced charge transfer applications in polymer solar cell (PSC) and trinitrotoluene (TNT) detection were studied respectively, and the results indicated that this polymer might be a good candidate material for PSC or detecting TNT in solution.
Poly(butylene terephthalate) (PBT) composites containing polyaniline (PANI) were prepared using a melt-blending process. Maleic anhydride-grafted PBT (PBT-g-MA) and PANI were used to improve the compatibility of PANI within the PBT matrix. PBT-g-MA/PANI composites exhibited noticeably superior mechanical properties compared with those of PBT/PANI due to greater compatibility with the added PANI. The antibacterial and antistatic properties of the composites were also evaluated. Escherichia coli were chosen as the standard bacteria for determining the antibacterial properties of the composite materials. The PBT-g-MA/PANI composites showed markedly enhanced antibacterial and antistatic properties compared to PBT/PANI composites due to the formation of imide bonds from condensation of the anhydride carboxyl acid groups of PBT-g-MA with the amino groups of PANI. The optimal level of PANI in the composites was 9 wt%, as excess PANI led to separation of the two organic phases, lowering their compatibility.
The thermal diffusivity of graphite intercalated compound (GIC)/polyamides (PA6, PA66 and PA12) and graphite/polyamides composites were investigated. The polyamides/GIC composites were prepared by an in-situ exfoliation melting process and thermal diffusivity of the composites was measured by a laser flash method. The surface chemistry of the GIC and graphite was investigated using Fourier transform infrared spectroscopy, the fracture morphology of the composites was observed by field emission scanning electron microscopy. The thermal diffusivity of the in-situ exfoliation processed PA/GIC composites showed a significant improvement over those of PA/expanded graphite intercalated compound composites and PA/graphite composites. We suggest that the larger flake size and high expansion ratio of the GIC during the in-situ exfoliation process leads to 3-dimensional conductive pathways and high thermal diffusivity. Thermal diffusivity of the polyamides/GIC (20 vol%) composites was increased approximately 18 times compared to that of pure polyamides.
Terephthalate (TA) intercalated layered double hydroxides (LDHs) were synthesized using hydroxides as raw materials, and poly(ethylene terephthalate) (PET)/LDH nanocomposites with different contents of TA intercalated LDHs were prepared by in-situ polymerization. The structure, morphology and thermal property of PET/LDH nanocomposites were investigated. The TA intercalated LDHs were partially exfoliated and well dispersed in PET matrix. The PET/LDH nanocomposites exhibit enhanced thermal stability relative to pure PET, confirmed by the thermogravimetric analysis results. The results of differential scanning calorimetry suggest that LDH nanoparticles could effectively promote the nucleation and crystallization of PET.
The electrical resistivity and thermal properties of multi-walled carbon nanotube/polypropylene (MWCNT/PP) composites have been investigated in the presence of coupling agents applied for improving the compatibility between the nanotubes and the polymer. A novel olefin-maleic-anhydride copolymer and an olefin-maleic-anhydride copolymer based derivative have been used as compatibilizers to achieve better dispersion of MWCNTs in the polymer matrix. The composites have been produced by extrusion followed by injection moulding. They contained different amounts of MWCNTs (0.5, 2, 3 and 5 wt%) and coupling agent to enhance the interactions between the carbon nanotubes and the polymer. The electrical resistivity of the composites has been investigated by impedance spectroscopy, whereas their thermal properties have been determined using a thermal analyzer operating on the basis of the periodic thermal perturbation method. Rheological properties, BET-area and adsorption-desorption isotherms have been determined. Dispersion of MWCNTs in the polymer has been studied by scanning electron microscopy (SEM).
Poly(lactic acid)/nano-precipitated calcium carbonate (PLA/NPCC) composites toughened with maleated styrene-ethylene/butylene-styrene (SEBS-g-MAH) were prepared by melt-compounding on a co-rotating twin-screw extruder followed by injection moulding. The mechanical properties of the PLA nanocomposites were characterized by tensile, flexural and impact tests, while their morphology were investigated using transmission electron microscopy (TEM). The thermal properties of the composites were examined with differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The elongation at break and impact strength of the PLA/NPCC nanocomposites increased significantly after addition of SEBS-g-MAH. Both nano-dispersed NPCC and small NPCC clusters were found in PLA matrix. Also, some SEBS-g-MAH encapsulated NPCC can be observed. Thermal stability of PLA/NPCC was enhanced prominently by the addition of SEBS-g-MAH.
Composites of natural rubber (NR)/vinyl polymer nanoparticles as polystyrene (PS) and poly(styrenemethacrylic acid) (P(S-MAA)) were prepared by heterocoagulation technique. The polymer nanoparticles were prepared by emulsifier-free emulsion polymerizations at 70°C using potassium persulfate as initiator. Under acidic condition where positive charge was present on the NR latex (NRL) surface, the nanoparticles having negative charge mainly from sulfate group of initiator were able to adsorb on the NRL surface, the electrostatic interaction being the driving force. The scanning electron micrographs showed that the polymer nanoparticles are homogenously distributed throughout NR matrix as nanoclusters with an average size of about 500 and 200 nm for PS and P(S-MAA), respectively. The mechanical properties of NR/PS and NR/P(S-MAA) composite films were compared with the NR host. The nanocomposites, particularly when the polymer nanoparticles are uniformly dispersed, possess significantly enhanced mechanical properties strongly depending on the morphology of the nanocomposites.