The Influence of Suspension Concentration on Quality of Multi-Wall Carbon Nanotube Buckypapers

Buckypaper is a thin sheet fabricated from aggregation of carbon nanotubes. In fact, buckypaper is a macroscopic aggregate of carbon nanotubes, or buckytubes. BuckyPaper can be folded and cut with scissors, like notebook paper. The generally accepted method for forming such carbon nanotube (CNT) films involves the use of ionic or non-ionic surfactants, such as Triton X-100 and Sodium lauryl sulfate, which improves their dispersibility in aqueous solution [1]. These suspensions can then be membrane filtered under negative or positive pressure to yield uniform films.While a large number of interesting properties and applications are reported for CNT, wide range applications of buckypapers are not surprising. A number of reported applications for buckypapers are: applied to the exteriors of airplanes, protection of electronic circuits and devices within airplanes from electromagnetic interference, act as a filter membrane to trap microparticles in air or fluid, fabrication of nano-composites as an effective armor plating, to illuminate computer and television screens, enhancement of heat conductivity that would allow computers and other electronic equipment to disperse heat more efficiently than is currently possible, and so on. Obviously, these applications are strongly dependent on buckypaper quality. In this way, the surface quality is the predetermination of quality of buckypaper. Due to microscopic size of the nanotubes and their bundles, using an appropriate microscope, like scanning electron microscope (SEM), is needful to characterize the surface quality of buckypapers. According to their SEM images, surface quality of buckypapers may be classified briefly as follow: a good surface quality has a smooth surface without deposited particles and a uniform rope network can be seen at high resolution. The fair surface may have a smooth surface at low magnification, but no clear rope network can be seen at high magnification. The poor surface has a rough surface quality at low magnification, and no rope network can be seen at high magnification [2]. However, the quality of a buckypaper, and hence its surface quality, is dependent on a number of parameters like nanotube type, suspension concentration, sonication time, sonication power, surfactant type, surfactant concentration, filtration differential pressure, and so on. Among these, the suspension concentration has an exceptional importance due to dependency of optimized value of the other parameters, such as sonication time, sonication power and surfactant concentration, to it. So, optimization of this parameter could give very important information about dependency of buckypaper quality to the other parameters, too. In addition, while effect of various parameters on quality of single wall CNT buckypapers was examined briefly [2, 3], there is not any reliable data about the effect of different parameters on quality of MWCNT buckypapers. Therefore, the main goal of this research work is to study the effect of suspension concentration on the quality of a multi-wall carbon nanotube buckypaper.