1. Comparison of the submicron structure and conductivity properties of multiwalled carbon nanotube polycarbonate composites using various microscopic methods
Bernadeth Kiss-Pataki1, Zsolt Endre Horváth1, Jyri Tiusanen2
1Research Center for Natural Sciences, Research Institute of Technical Physics and Materials Science - MFA, Hungarian Academy of Sciences.
2Promolding BV
MOTIVATION:
The nanometer size of the fillers in nanocomposites renders more difficulty on their microscopic characterization. Characterization of the dispersion of CNT agglomerates is still considered as a demanding task. Differences in size distribution of the agglomerates under the optical diffraction limit can result in significant differences in bulk composite properties. In such cases the widely applied transmission optical microscopy (TOM) cannot provide proper structural information for satisfactory materials characterization. Moreover artefacts produced during TOM sample preparation are comparable in size with the real structural features.
In case of CNT polymer composites the substantial conductivity difference between the filler and the matrix provides a way of application of the conductive tip atomic force microscopy (CT-AFM) method to the characterization CNT dispersion in polymer composites. The resolution of the CT-AFM is far better than the transmission optical microscopes resolution, whereas this difference in conductivity enables the obvious separation of conductive parts from insulating matrix. Considering the working principle of the method, the artefacts influencing the topography of the sample surfaces essentially are not involved in the obtained image. Moreover the resulted images could be processes for statistical analysis, so their automatisation seems easier, not as in case of TEM and SEM images.
RESULTS:
PC97CNT3; tm=300°C; iv=30 mm/s; VR=46.46 Ωcm
PC97CNT3; tm=320°C; iv=42 mm/s; VR=23.27 Ωcm
PC97CNT3; tm=280°C; iv=42 mm/s; VR= Ωcm
CONCLUSIONS:
EXPERIMENTAL:
The analyses were carried out with the aid of the transmission optical (TOM) and transmission electron microscopy (TEM). A Leica Ultracut S ultra microtome was used to attain the adequate thickness of samples. TEM analyses were made by a Philips CM 20 Microscope, and optical microscopy observation was completed using an Olympus BH2 transmission optical microscope with a Leica DFC 280 digital camera. Conductive atomic force microscopy (C-AFM) investigations were performed on previously flattened surface of samples, using a glass knife of a Leica Ultracut Ultramicrotome. The sample then was fixed to the sample holder by a carbon paste. A Multimode 8 AFM (Bruker) was operated using the same type 20 nm Pt-Ir AFM probe, in the C-AFM mode to capture the conductive AFM images, setting the following parameters under ambient conditions and room temperature: 100 pA current sensitivity and 100 mV DC sample bias voltage, in 10 μm scanning area, with 512x512 pixel resolutions. The so obtained images were binarized, and evaluated according to the transmission optical microscopic image processing method.
The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7-PEOPLE-ITN-2008) under grant agreement number
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