Svitlana Trotsenko

Zero Bias Anomaly in an Individual Suspended Electrospun Nanofiber

We report observing a double broad Kondo-like zero bias conductance peak at low temperatures in individual suspended electrospun nanofibers Poly(methyl methacrylate)- multiwalled carbon nanotubes. This anomalous behavior is suppressed at higher temperatures. We attribute this to the existence of correlated double impurity system inside the nanofiber. From the results we calculate a Kondo-like temperature for the nanofiber to be ~31.7-34K.

Mechanical Properties of Individual Composite Poly(methyl-methacrylate) - Multiwalled Carbon Nanotubes Nanofibers

Multiwalled carbon nanotubes with their superb mechanical properties are an unique filler material for polymer composites. Here, we present an investigation of mechanical properties of electrospun Poly-(methyl-methacrylate) multiwalled carbon nanotubes composite nanofibers. The method of electrospinning was used to fabricate suspended individual Poly-(methyl-methacrylate) multiwalled carbon nanotubes nanofibers. In order to reinforce the nanofibers, different high concentration of multiwalled carbon nanotubes were used. Transmission electron microscopy measurements reveal a successful filling of the nanofibers. The different types of nanofibers were deposited at SiO2 substrates. Which were previously etched, to create trenches for bend tests. Followed by fixing the nanofiber with a focus ion beam platinum deposition at the trench edges. An atomic force microscopy was used to perform the mechanical nanofiber bending tests over trenches. The results were compared with pristine Poly-(methyl- methacrylate) nanofibers to nanofibers with 15 weight% and 20 weight% multiwalled carbon nanotubes composite fibers. We observed that pristine nanofibers have Youngs modulus of 136 MPa, while for composite nanofibers with 15 weight% have 2.65 GPa and with 20 weight% have 6.06 GPa (at room temperature and air ambiance). This corresponds to an increase of Youngs modulus of 19 fold between the pristine nanofibers and the 15 weight% of mutliwalled carbon nanotubes filled nanofibers. Therefore the increase of the Youngs modulus compared between the pristine and the 20 weight% MWCNT filled nanofibers corresponds to 45 fold.

Carbon nanotubes based engineering materials for thermal management applications

We developed innovative solutions for reaching high performance in carbon-nanotube-filled engineering materials. Electrospinning was applied to improve the thermal conductivity in polymer composites via the alignment of nanotubes in a polymer matrix. Alignment was achieved by flow-confinement and charge-induced alignment during electrospinning. Additionally, the use of liquid crystal polymer as a matrix increased the degree of alignment leading to the remarkable increase of the thermal conductivity in composites by a factor 33. We developed the reduction from method to produce metal-matrix composites filled with carbon nanotubes. We were able to engineer the coefficient of thermal expansion (CTE) of the copper composite, for example 3 wt% of carbon nanotubes added to copper yielded CTEs comparable with ceramics and semiconductors. In situ thermal polymerization of natural oils (plant and fish) was applied to produce nanotubes-based thermal greases. This method creates novel, environmentally friendly thermal grease with excellent thermal conductivity (increased by a factor 12), that is easy to handle compound and to remove. Such thermal greases can be applied to surfaces by various methods, including screen printing, and demonstrate good thermal stability, reduced thermal expansion, and no pumping-out effect.