Multi-functional carbon nanotube composites with super-hydrophobic properties

Polymer composites containing conducting fillers have been extensively investigated for various applications such as electromagnetic interference (EMI) shielding, electronic packaging, radar absorption, structural reinforcement, high charge storage capacitors and heating units. [1-4] High aspect ratio fillers which attain electrical percolation at low volume fractions are exceedingly desirable due to the structural integrity and electronic properties of the resulting composites. In addition, while carbon based materials, such as carbon black and fibers, have previously been used in polymer composites, their widespread use is limited due to a maximum loading capability, beyond which there is embrittlement. Carbon nanotubes (CNTs) are then more attractive candidates for filler materials in composites, primarily due to their large aspect ratio and tunable electrical conductivity, which enables electrical percolation to be achieved with very small amounts of nanotubes. For example, we have calculated from the excluded-volume percolation theory of rod-like systems [5] that single walled CNTs (SWNTs) with an aspect ratio of ~ 5000 (which corresponds to a length of 5 μm and a diameter of ~ 1 nm), when dispersed uniformly into a non-conducting polymer enable a conducting pathway at a volume fraction of ~ 0.01 %. CNTs offer an attractive option in this regard; they exhibit an extremely high aspect ratio which can reach up to 10. This coupled with a large interfacial area (> 1300 m/g), allows composites which use CNT filler to have mechanical and microwave properties that far exceed those of the initial polymer matrix. [6-9] However, there are still several challenges to the utilization of CNTs, e.g., (a) aggregation and bundling which leads to a non-uniform dispersion, along with (b) poor interfacial bonding of the nanotubes with the polymer matrix, both of which lead to variable composite characteristics, along with the (c) high cost of CNTs. In addition, most current research on nanocomposites has focused on their bulk attributes, i.e., electrical, microwave, thermal and mechanical properties. In practical applications, surface properties such as robustness against environment contamination are critical design considerations if intrinsic properties are to be maintained. Superhydrophobic surfaces with a water contact angle (WCA) above 150° and water sliding angle lower than 5° have attracted extensive research interest for both scientific and practical engineering field. [10-12] Due to its effective convenience, development of superhydrophobic surfaces and materials have been investigated for various applications such as anti snow sticking, blood compatibility, self cleaning, and micro-fluidic systems. In general, a combination of surface roughness at both the microand nanostructures with low surface energy material is desirable for superhydrophobic surface. Among several approaches to achieve superhydrophobic surface such as chemical etching and nanotube array, solvent casting method is one of facile approaches for practical applications. [13-15] With a proper solvent and temperature condition, polypropylene (PP) coating has a WCA of 160° on the substrates forming porous coating when the solvent is evaporated. [11] Incorporated with conjugated conducting polymer, solvent casting 45th International Symposium on Microelectronics | September 9-13, 2012 | San Diego, California USA