Experimental evaluation of thermal stability of PS- MWCNT nanocomposite as a real-time dosimeter

Introduction: Carbon nanotubes (CNTs) are ideal reinforcing fillers for a polymer matrix, because of their nanometer size, high aspect ratio and, more importantly, their excellent mechanical strength, and electrical and thermal conductivity. The CNTs are categorized into two groups: SWCNT and MWCNT. MWCNTs would have diameters ranging from 2 to 100 nm and lengths of up to tens of microns, and they exhibited electrical conductivity as high as 105–107 S/m. The most promising theories for explaining electrical behavior in polymer nanocomposites are based on hopping conductivity models developed to understand the charge transport in disordered semiconductors and amorphous solids. The probability of an electron hopping from one localized state to another one depends on temperature. The authors in the previous articles introduced a novel dosimeter applied in diagnostic and therapeutic dosimetry.
The objective of this experimental work is to evaluate the thermal stability of PS/MWCNT (0.28 wt%) nanocomposite as a real-time dosimeter for the diagnostic and therapeutic purposes.
Materials and Methods: MWCNT with purity of 98 wt%, density of 2.1 g/cm3, outside diameter: 5-15 nm, inside diameter: 3-5 nm, average length: 50 μm, SSA: ~233 m2/g, electrical conductivity greater than 104 S/m was prepared from US Nano Inc, and finally high purity toluene and DCM as the solvents were purchased from Merck Company. PS 1540 with the density 1.05 g/cm3 was supplied by Tabriz Petrochemical Company. Solution processing has been used to prepare 0.28 wt% PS/MWCNT nanocomposite for dosimetry purposes.
Results: Electric resistance of the nanocomposites in different temperatures was measured. Results showed that a positive temperature coefficient (PTC) effect from the room temperature until the glass transition temperature (Tg) for the sample was exhibited, and after that, the negative temperature coefficient (NTC) effect was observed. The maximum discrepancy in the resistance for the sample at room temperature until 50°C was 15%.
Conclusion: In this experimental work, the variation of electric resistance with temperature for the 0.28 wt% MWCNT-PS nanocomposite at room temperature until 80°C was measured, in which indicated a PTC effect before glass transition temperature of polystyrene and NTC effect after that. It can be concluded that for applying this material in a dosimeter, regarding the temperature dependence of the aforementioned nanocomposite, there is need to insert a temperature correction factor in the extracted data for dosimetry purposes. This research work motivates the investigation in depth of the thermal properties behavior of polymer- CNT nanocomposites as a real-time dosimeter.