Radius and chirality dependent conformation of polymer molecule at nanotube interface

Temperature dependent conformations of linear polymer molecules adsorbed at carbon nanotube (CNT) interfaces are investigated through molecule dynamics simulations. Model polyethylene (PE) molecules are shown to have selective conformations on CNT surface, controlled by atomic structures of CNT lattice and geometric coiling energy. PE molecules form entropy driven assembly domains, and their preferred wrapping angles around large radius CNT (40, 40) reflect the molecule configurations with energy minimums on a graphite plane. While PE molecules prefer wrapping on small radius armchair CNT (5, 5) predominantly at low temperatures, their configurations are shifted to larger wrapping angle ones on a similar radius zigzag CNT (10, 0). A nematic transformation around 280 K is identified through Landau-deGennes theory, with molecule aligning along tube axis in extended conformationsComment: 19 pages, 7 figure2, submitted to journa

Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors

Chemical sensing properties of single wire and mat form sensor structures fabricated from the same carbon nanotube (CNT) materials have been compared. Sensing properties of CNT sensors were evaluated upon electrical response in the presence of five vapours as acetone, acetic acid, ethanol, toluene, and water. Diverse behaviour of single wire CNT sensors was found, while the mat structures showed similar response for all the applied vapours. This indicates that the sensing mechanism of random CNT networks cannot be interpreted as a simple summation of the constituting individual CNT effects, but is associated to another robust phenomenon, localized presumably at CNT-CNT junctions, must be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and Processing 201

Double walled carbon nanotube/polymer composites via in-situ nitroxide mediated polymerisation of amphiphilic block copolymers

Because of their unique physical, chemical, and structural properties, carbon nanotubes (CNT) are playing an increasingly important role in the development of new engineering materials [1]. Across many different applications, CNT/polymer composites have been extensively studied [2] S.B. Sinnot and R. Andrews, Carbon nanotubes: synthesis, properties, and applications, Crit Rev Solid State Mater Sci 26 (2001), pp. 145–249.[2]. The key problem for CNT/polymer composite elaboration is the dispersion, compatibilization, and stabilization of the CNT in the polymer matrix. To solve this problem, a structure with di-block copolymers, one with a good affinity to CNT (monomer M1), the other being the matrix (monomer M2), is proposed in this study, as shown on the two steps mechanism of Fig. 1

Role of the particle size polydispersity in the electrical conductivity of carbon nanotube-epoxy composites

Carbon nanotubes (CTNs) with large aspect-ratios are extensively used to establish electrical connectedness in polymer melts at very low CNT loadings. However, the CNT size polydispersity and the quality of the dispersion are still not fully understood factors that can substantially alter the desired characteristics of CNT nanocomposites. Here we demonstrate that the electrical conductivity of polydisperse CNT-epoxy composites with purposely-tailored distributions of the nanotube length L is a quasiuniversal function of the first moment of L. This finding challenges the current understanding that the conductivity depends upon higher moments of the CNT length. We explain the observed quasiuniversality by a combined effect between the particle size polydispersity and clustering. This mechanism can be exploited to achieve controlled tuning of the electrical transport in general CNT nanocomposites.Comment: 9 pages, 5 figure

High-Yield of Memory Elements from Carbon Nanotube Field-Effect Transistors with Atomic Layer Deposited Gate Dielectric

Carbon nanotube field-effect transistors (CNT FETs) have been proposed as possible building blocks for future nano-electronics. But a challenge with CNT FETs is that they appear to randomly display varying amounts of hysteresis in their transfer characteristics. The hysteresis is often attributed to charge trapping in the dielectric layer between the nanotube and the gate. This study includes 94 CNT FET samples, providing an unprecedented basis for statistics on the hysteresis seen in five different CNT-gate configurations. We find that the memory effect can be controlled by carefully designing the gate dielectric in nm-thin layers. By using atomic layer depositions (ALD) of HfO$_{2}$ and TiO$_{2}$ in a triple-layer configuration, we achieve the first CNT FETs with consistent and narrowly distributed memory effects in their transfer characteristics.Comment: 6 pages, 3 figures; added one reference, text reformatted with smaller addition

Systematically extending classical nucleation theory

The foundation for any discussion of first-order phse transitions is Classical Nucleation Theory(CNT). CNT, developed in the first half of the twentieth century, is based on a number of heuristically plausible assumtptions and the majority of theoretical work on nucleation is devoted to refining or extending these ideas. Ideally, one would like to derive CNT from a more fundamental description of nucleation so that its extension, development and refinement could be developed systematically. In this paper, such a development is described based on a previously established (Lutsko, JCP 136:034509, 2012 ) connection between Classical Nucleation Theory and fluctuating hydrodynamics. Here, this connection is described without the need for artificial assumtions such as spherical symmetry. The results are illustrated by application to CNT with moving clusters (a long-standing problem in the literature) and the constructrion of CNT for ellipsoidal clusters

Improving oxidation resistance of carbon nanotube nanocomposites for aerospace applications

Carbon nanotubes (CNTs) based materials possess strong potential to substitute various functional materials developed exclusively for aerospace applications. However, because of the low oxidation temperature of CNTs (400-500 oC), using CNT based ceramic nanocomposites in high temperature applications can be problematic. Making ceramic-CNT nanocomposites by atomic layer deposition (ALD) method and field assisted sintering technology (FAST) is a good route to improve oxidative stability of CNTs. In this study, thermo-gravimetric analysis (TGA) of alumina coated CNTs (prepared by ALD) and alumina-CNT nanocomposites (prepared by FAST) were carried out. 16% improvements were observed in the oxidation resistance for alumina-CNT nanocompo-sites prepared by ALD and SPS techniques. Different strategies to improve oxidation resistance are discussed