جستجوی مقالات مرتبط با کلیدواژه « walled carbon nanotubes » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Electromagnetic compatibility (EMC) and electromagnetic interference (EMI) have emerged as key issues with respect to commercial and military purposes in association with electromagnetic waves. The importance of protection against electromagnetic interference in wireless communication and electronic toll collection (ETC) systems has undoubtedly increased over the years. Generally، the electromagnetic absorption properties of material depend on their intrinsic electromagnetic properties such as conductivity، magnetic permeability and dielectric constant and also factors such as thickness and frequency. The effect of each parameter on the absorption performance is yet difficult to comprehend due to the complexity of electromagnetic waves propagation in different media. Addition of pure dielectric or magnetic material to a polymer matrix is a possible way to change electromagnetic properties of the materials. In this study nanocomposites of polystyrene/multi-walled carbon nanotubes were prepared using a solution method with three different homogenizer speeds for the purpose of nanotube dispersion and evaluation of the effect of nanotube dispersion on the electromagnetic wave absorption properties. The morphology of the nanocomposits was investigated by scanning electron microscopy (SEM). The capability and properties of electromagnetic wave absorption of nanocomposites were studied in the frequency range of 5 to 8 GHz using a vector network analyzer and finally the results of their absorption were compared with each other. It was found that by improving the dispersion of nanoparticles، both the amount and bandwidth of absorption increase. Moreover، by increasing the homogenizer speed up to 10000 rpm the maximum reflection loss was reported to occur at 8 GHz.

Most recent studies on polymer nanocomposites containing carbon nanotubes include mechanical، rheological، thermal and electrical properties. Optical properties of polymer nanocomposites containing carbon nanotubes are not very clear. Accordingly، in the present work، the optical properties of these naocomposites are studied in the visible region of electromagnetic spectrum. To do that، PMMA nanocomposites including different percentages of carbon nanotubes (CNTs) and carbon black are prepared by applying melt mixing method. To characterize the optical properties، the spectral reflectance values of the prepared samples are measured by a reflectance spectrophotometer with d/8 geometry in the visible region from 400-700 nm. The color parametric values a*، b* and L* of the samples are calculated in CIELAB color space under a simulator of the day light i. e.، D65 and the observer 1964 (10°). For all forms of samples، i. e. powder and different prepared nanocomposites، the blackness index، proposed by Westland and et al.، is calculated. For the latter، the transmission electronic microscope (TEM) images are obtained، also. As a result، with increasing the nanotube content up to 0. 5 %wt، the spectral reflectance factors decreases down to 7% and the blackness content of the samples increases. In addition، the results show in comparison with carbon black، the samples containing carbon nanotubes represent a better blackness index. The TEM images show that for specific carbon nanotube content، the spreading CNT by melt mixing method is better than solution method. It seems that CNT can replace carbon black by its more efficient distribution by an appropriate method such as melt mixing.