Alternating current electrical conductivity of high-density polyethylene-carbon nanofiber composites.

High-density polyethylene (HDPE)-carbon nanofiber (CNF) composites with good dispersion of fillers in the polymer matrix were melt-compounded in a Haake mixer. The dependences of the alternating current conductivity of such nanocomposites on the filler content, temperature, and DC bias were investigated. The results showed that the electrical conducting behavior of HDPE-CNF nanocomposites can be well characterized by the direct current conductivity (sigmaDC, characteristic frequency (fc) and critical exponent (s). It was found that sigmaDC of percolating HDPE-CNF nanocomposites increases with increasing filler concentration and follows the scaling law of percolation theory. Increasing temperature caused a reduction of sigmaDC, leading to the occurrence of positive-temperature-coefficient effect near the melting temperature of HDPE matrix. Application of DC bias led to an increase of sigmaDC due to the creation of additional conducting paths within the polymer composites. The characteristic frequency generally followed the same tendency as sigmaDC. The s values of percolating composites were slightly higher than those predicted by the percolation theory, indicating the presence of tunneling or hopping conduction in these composites.

Surface characteristics, mechanical properties, and cytocompatibility of oxygen plasma-implanted porous nickel titanium shape memory alloy.

Good surface properties and biocompatibility are crucial to porous NiTi shape memory alloys (SMA) used in medical implants, as possible nickel release from porous NiTi may cause deleterious effects in the human body. In this work, oxygen plasma immersion ion implantation (O-PIII) was used to reduce the amount of nickel leached from porous NiTi alloys with a porosity of 42% prepared by capsule-free hot isostatic pressing. The mechanical properties, surface properties, and biocompatibility were studied by compression tests, X-ray photoelectron spectroscopy (XPS), and cell culturing. The O-PIII porous NiTi SMAs have good mechanical properties and excellent superelasticity, and the amount of nickel leached from the O-PIII porous NiTi is much less than that from the untreated samples. XPS results indicate that a nickel-depleted surface layer predominantly composed of TiO(2) is produced by O-PIII and acts as a barrier against out-diffusion of nickel. The cell culturing tests reveal that both the O-PIII and untreated porous NiTi alloys have good biocompatibility.