Hybrid Carbon Fibers/Carbon Nanotubes Structures for Next Generation Polymeric Composites

Pitch-based carbon fibers are commonly used to produce polymeric carbon fiber structural composites. Several investigations have reported different methods for dispersing and subsequently aligning carbon nanotubes (CNTs) as a filler to reinforce polymer matrix. The significant difficulty in dispersing CNTs suggested the controlled-growth of CNTs on surfaces where they are needed. Here we compare between two techniques for depositing the catalyst iron used toward growing CNTs on pitch-based carbon fiber surfaces. Electrochemical deposition of iron using pulse voltametry is compared to DC magnetron iron sputtering. Carbon nanostructures growth was performed using a thermal CVD system. Characterization for comparison between both techniques was compared via SEM, TEM, and Raman spectroscopy analysis. It is shown that while both techniques were successful to grow CNTs on the carbon fiber surfaces, iron sputtering technique was capable of producing more uniform distribution of iron catalyst and thus multiwall carbon nanotubes (MWCNTs) compared to MWCNTs grown using the electrochemical deposition of iron. 1. Introduction The attractive properties of carbon nanotubes [1] (CNTs) might be attributed to their unique and minimum defect nanostructure. Single wall carbon nanotubes (SWCNTs) possess exceptional mechanical [2, 3], thermal, and electric properties [4] compared to graphite, Kevlar, SiC, and alumina fibers. The strength, elastic modulus, and fracture properties of CNTs are an order of magnitude higher than most common composites used in civilian and military applications [5–8]. Moreover, CNTs reinforcement was proven to increase the toughness of the polymers and composite to absorb impact energy [9–12]. Most research to date had focused on using CNTs as a reinforcement or as a filler in a polymeric matrix by dispersing and perhaps subsequently aligning single- or multiwalled CNTs in the matrix [13, 14]. Alignment and dispersion are critical factors that are difficult to control experimentally using oft-repeated mixing methods. CNTs embedded in a polymeric matrix form aggregates of themselves that are not only poorly adhered to the matrix but also concentrate stresses, compromising the effect of the CNTs as reinforcement. Sonication [15] and calendaring [16] have been used to mitigate this problem, but these techniques are not effective beyond ~3% CNTs weight fraction due to the formation of aggregates [17]. The extreme difficulty in uniformly dispersing CNTs in polymer matrices arises from the large surface area of CNTs [18]. Dispersion and extrusion