Giant Surface Conductivity Enhancement in a Carbon Nanotube Composite by Ultraviolet Light Exposure

Abstract

Carbon nanotube composites are lightweight, multifunctional materials with readily adjustable mechanical and electrical properties-relevant to the aerospace, automotive, and sporting goods industries as high-performance structural materials. Here, we combine well-established and newly developed characterization techniques to demonstrate that ultraviolet (UV) light exposure provides a controllable means to enhance the electrical conductivity of the surface of a commercial carbon nanotube-epoxy composite by over 5 orders of magnitude. Our observations, combined with theory and simulations, reveal that the increase in conductivity is due to the formation of a concentrated layer of nanotubes on the composite surface. Our model implies that contacts between nanotube-rich microdomains dominate the conductivity of this layer at low UV dose, while tube-tube transport dominates at high UV dose. Further, we use this model to predictably pattern conductive traces with a UV laser, providing a facile approach for direct integration of lightweight conductors on nanocomposite surfaces.

Impact of UV irradiation on multiwall carbon nanotubes in nanocomposites: Formation of entangled surface layer and mechanisms of release resistance

“…The SEM images showed the formation of a MWCNT surface layer on the sample (Figure 6). In a previous study, the electrical conductivity of the MWCNT surface layer after UV degradation was found to be five times greater than that of the bulk 3.5 % MWCNT nanocomposite [49]. A roughly similar thickness of the MWCNT surface layer was observed after UV irradiation in this study for two doses: 775 MJ/m 2 (data not shown) and a much higher dose of 4865 MJ/m 2 .…”

“…This finding suggests that the MWCNT surface layer was effectively shielding the epoxy matrix underneath from further degradation, thus limiting growth in the thickness of the MWCNT surface layer. Based on experimental evidence, theory, and simulation, the high electrical conductivity MWCNT surface layer formed by UV irradiation has been postulated as due to a combination of matrix removal and densification of the MWCNT-rich domains in the nanocomposites [49]. …”

Universal interrelation between measures of particle and polymer size

“…28 (c) Dense cluster of multi-walled carbon nanotubes often observed in commercial nanotube materials. 41 (d) A sampling of globular proteins from the protein data bank. 43 holds to a good approximation, and we provide the effective scaling exponents ν eff in Table II.…”

Bright focused ion beam sources based on laser-cooled atoms

“…20 shows Li + MOTIS-based microscopy of a carbon nanotube-based composite, where charge-based contrast allows clear differentiation between the conducting carbon nanotube bundles and the insulating epoxy matrix. 161 Because the ion beam consists of positive ions, the insulating areas accumulate a net positive charge and hence do not readily release secondary electrons. This causes them to appear black.…”

“…Image is of a cleaved face tilted toward the beam by 8 degrees, and shows a carbon nanotube mat formed on the surface by UV exposures (see Ref. 161 ). …”