Runqing Ou

Assessment of percolation and homogeneity in ABS/carbon black composites by electrical measurements

In this study, composites consisting of an insulating poly(acrylonitrile-co-butadiene-co-styrene) polymer matrix and a conducting carbon black (CB) additive were produced by twin-screw extrusion. Both direct current and alternating current electrical measurements were used to evaluate the electrical properties of the composite and to assess whether sufficient mixing was achieved. Electrical measurement results and scanning electron micrographs show that once-extruded composites had a porous structure and poor conductivity while twice-extruded composites were much more homogeneous and had higher conductivity. The percolation threshold of the twice-extruded poly(acrylonitrile-co-butadiene-co-styrene)/CB composites was found to be between 8 and 10% CB. Electrical measurements provided a feedback loop for improving processing of the composite material.

Effect of the fabrication method on the electrical properties of poly(acrylonitrile-co-butadiene-co-styrene)/carbon black composites

Poly(acrylonitrile-co-butadiene-co-styrene) (ABS), an engineering plastic, was combined with carbon black (CB) to increase its conductivity. The ABS/CB composites were prepared using two different methods: dissolution of ABS in Butan-2-one and manual mixing of the constituent materials. These fabrication methods led to different microstructures, which led to vastly different electrical properties. The microstructures were acquired using scanning electron microscopy (SEM) and optical microscopy, while the electrical conductivity was obtained using impedance spectroscopy. The percolation threshold of the composites fabricated using the manual mixing method was found to be much lower (0.0054 vol.% CB) than that of the composites fabricated using the dissolution method (2.7 vol.% CB).

Detection of percolating paths in polyhedral segregated network composites using electrostatic force microscopy and conductive atomic force microscopy

Composite specimens possessing polyhedral segregated network microstructures require a very small amount of nanosize filler, <1 vol %, to reach percolation because percolation occurs by accumulation of the fillers along the edges of the deformed polymer matrix particles. In this paper, electrostatic force microscopy (EFM) and conductive atomic force microscopy (C-AFM) were used to confirm the location of the nanosize fillers and the corresponding percolating paths in polymethyl methacrylate/carbon black composites. The EFM and C-AFM images revealed that the polyhedral polymer particles were coated with filler, primarily on the edges as predicted by the geometric models provided.

Self-assembly of carbon black into nanowires that form a conductive three dimensional micronetwork

The authors have used mechanical self-assembly of carbon-black nanoparticles to fabricate a three dimensional, electrically connected micronetwork of nanowires embedded within an insulating, supporting matrix of poly(methyl methacrylate). The electrical connectivity, mean wire diameter, and morphological transitions were characterized as a function of the carbon-black mass fraction. Conductive wires were produced with mean diameters as low as 24nm with lengths up to 100μm.

In-plane impedance spectroscopy of doped polyaniline films

In-plane impedance measurements were made on lightly doped polyaniline (PANI) films. A Debye-like conductivity relaxation was observed for HCl-doped PANI samples. The relaxation shifts to higher frequency as the doping level is increased. The conductivity shows a dramatic increase at low doping levels and levels off at higher doping levels. The in-plane conductivity is over three orders of magnitude higher than the through-plane conductivity.

Study of Percolation in PMMA / Indium Tin Oxide Composites

Knowledge of percolation in binary composites is critical to the development of new materials with specific electrical and optical properties. This report investigates the detection of percolation in novel two-phase composites consisting of poly(methyl) methacrylate(PMMA) and indium tin oxide (ITO). ITO is a filler of particular interest primarily for possessing optical clarity consistent with PMMA in the visible light range. AC impedance measurements were performed on specimens with varying concentrations of ITO particles to determine the percolation threshold. Percolation was observed when specimens contained 2-3% vol. of nano- sized ITO and 6%-8% vol. of coarse-sized ITO. Thus, the percolation threshold appeared significantly decreased with reduced particle size of the filler. It is speculated that minor agglomerates in the bulk of the specimens may have prevented percolation from occurring at even lower volume fractions of the filler phase.

Three Dimensional Structure-Electrical Properties of Oriented PPV and PANI Films

In this paper the influence of anisotropic molecular structure on the three dimensional electrical properties of both poly(phenylene vinylene), (PPV), and polyaniline, (PANI) oriented films is investigated. The anisotropic structure of the stretched PPV and PANI EB films were examined using a modified waveguide coupler while three dimensional impedance spectroscopy measurements were made using specially designed test fixtures that allowed the in-plane as well as the through-plane impedance to be measured. The unstretched PANI EB film has a random orientation and one-way stretching leads to a uniaxial structure. The unstretched PPV film, on the other hand, was found to have a highly planar structure and oneway stretching converts the planar structure to a uniaxial structure. Impedance measurements were made on PANI after it was doped with HCl while PPV films were measured in the undoped state. For HCl-doped PANI films, the conductivity along the stretch direction was found to increase with orientation. For undoped PPV films, the conductivity through the film thickness direction decreased with increasing orientation. For both polymers, the in-plane conductivity was significantly greater than the through-plane conductivity.Copyright