Motion, carbon nanotubes

Section I reviews the new concepts and applications of nanotechnology for catalysis. Chapter 1 provides an overview on how nanotechnology impacts catalyst preparation with more control of active sites, phases, and environment of actives sites. The values of catalysis in advancing development of nanotechnology where catalysts are used to facilitate the production of carbon nanotubes, and catalytic reactions to provide the driving force for motions in nano-machines are also reviewed. Chapter 2 investigates the role of oxide support materials in modifying the electronic stmcture at the surface of a metal, and discusses how metal surface structure and properties influence the reactivity at molecular level. Chapter 3 describes a nanomotor driven by catalysis of chemical reactions. 

Interaction-induced absorption by the vibrational or rotational motion of an atom, ion, or molecule trapped within a Ceo cage, so-called endohedral buckmin-sterfullerene, has excited considerable interest, especially in astrophysics. The induced bands of such species are unusual in the sense that they are discrete, not continuous they may also be quite intense [127]. Other carbon structures, such as endohedral carbon nanotubes, giant fullerenes, etc., should have similar induced band spectra [128], but current theoretical and computational research is very much in flux while little seems to be presently known from actual spectroscopic measurements of such induced bands. 

Single molecule motion within a carbon nanotube... 

Atomic Force Microscopy Atomic force microscopy is a direct descendant of STM and was first described in 1986 [254], The basic principle behind AFM is straightforward. An atomically sharp tip extending down from the end of a cantilever is scanned over the sample surface using a piezoelectric scanner. Built-in feedback mechanisms enable the tip to be maintained above the sample surface either at constant force (which allows height information to be obtained) or at constant height (to enable force information to be obtained). The detection system is usually optical whereby the upper surface of the cantilever is reflective, upon which a laser is focused which then reflects off into a dual-element photodiode, according to the motion of the cantilever as the tip is scanned across the sample surface. The tip is usually constructed from silicon or silicon nitride, and more recently carbon nanotubes have been used as very effective and highly sensitive tips. 

Figure 7.18 Direct observation of motions of the Er3N cluster and Er3N 4-C8o in CNTs (a) HRTEM images (upper, taken at 37 s lower, taken at 2 s) (b) suggested orientations (c) simulated images [185]. (Reprinted with permission from Y. Sato, et al., Structures of Dsd-Cso and 7h-Er3N C8o fullerenes and their rotation inside carbon nanotubes demonstrated by aberration-corrected electron microscopy, Nano Letters, 7, 3704-3708, 2007. 2007 American Chemical Society).

Actuators based on the swelling and shrinking of gels are the subject of much research. They can be regarded as modeling muscle systems. However, the response times of such systems are limited, because actuator motion occurs with molecular diffusion in the gel. If each molecule could expand and shrink instead, motional response times would significantly improve. Carbon nanotubes are known to expand or shrink upon injections of electrons or... 

The structure and properties of C2o (8,8) CNT system are explored by quantum chemical and molecular mechanic calculations. The change of the barrier for relative motion of fullerene along the carbon nanotube axis at the Peierls transition is found. The changes of dynamical behavior of the system C2o (8,8) CNT at the transition are discussed. 

A possibility of encapsulation of small fullerenes inside carbon nanotubes (CNTs) was considered recently [1], It was shown that the armchair (8,8) nanotube is the smallest CNT which can encapsulate the fullerene C20 [1]. We use the semiempirical PM3 molecular orbital method with periodic boundary conditions along the nanotube axis [2] to study the structure and properties of the system C2o (8,8) CNT. The PM3 method [3] was used previously to study the fullerene C20 [4] and to calculate the Kekule structure of the ground state of the (5,5) CNT [5]. To explore the relative motion of C20 inside the (8,8) CNT we additionally implemented molecular mechanics (MM+) calculations [6]. 

Recently, single chains of synthetic polymers have been visualized and examined regarding their conformation.79 81131 133 Mostly these were molecules with a well defined rather invariant shape like fullerenes, carbon nanotubes, and some polymer molecules. In this review we will focus on less rigid or even soft hyperbranched polymer molecules (Figure 1) (i) their visualization followed by analysis of the conformation and motion and (ii) probing of their properties such as specific interactions and mechanical properties. For comparison, some relevant examples from biomacromolecules are discussed. 

Sliding between concentric multiwalled carbon nanotubes presents a simple geometry, which restricts interlayer motion to a single (axial) direction with a fixed interlayer orientation of stiff, smooth layers. Each layer in a concentric multiwalled carbon nanotube is indexed by two integers (n, m) that give the circumference in graphitic lattice coordinates. The difference in radii between successive layers frustrates the circumferential interlayer registry. The axial... 

The molecular dynamics (MD) simulations for carbon nanotubes were carried out using the Discover module of the commercial software package supplied by Biosym Technologies Inc., USA in SiliconGraphics-IRIS 4D/30 workstation. The motion of the nuclei on the potential energy surface of the system with energy E(R) is described by Newton s equation of motion as follows ... 

The concept of single-file diffusion has most successfully been applied for MD simulations in carbon nanotubes [36-39], yielding both the square-root time dependence of the molecular mean square displacement and a remarkably high mobility of the individual, isolated diffusants. In [40-42], the astonishingly high single-particle mobilities in single-file systems have been attributed by MD simulations to a concerted motion of clusters of the adsorbed molecules. 

New method to control the motion of carbon nanotube-based nanoelectromechanical systems is proposed. Chemosorption of atoms and molecules on open edges of a single-walled carbon nanotube leads to the appearance of electric dipole moment. In this case the nanotube can be actuated by non-uniform electric field. Electric dipole moments of the carbon nanotubes with functionalized edges are calculated. The method proposed is demonstrated with an example of gigahertz oscillator. 

Warner, J. H., Ito, Y., Riimmeli, M. H., Buchner, B., Shinohara, H., and Briggs, G. A. D. 2009. Capturing the motion of molecular nanomaterials encapsulated within carbon nanotubes with ultrahigh tempoi al resolution. ACS Nano 3 3037-3044. 

There is growing interest in biomimetic motions, which imitate the action of natural muscles. Since such motions are difficult to realize using conventional appliances such as mechanical, hydraulic, or pneumatic actuators, research efforts are focused on the development of new muscle-like actuators. Electroactive polymers (EAPs) including polymer gels [63], ionic polymer-metal composites (IMPCs) [64], conductive polymers [56], and carbon nanotubes [65] are candidates to address the performance demands. 

Admittedly, these results pertain to a worst case scenario a one-dimensional bond network with no external constraints. Similar comparisons have been made for carbon nanotubes [23], which are much more highly connected. In this case, the agreement is much better in that the nanotube keeps its shape in the MD simulations however, the magnitude of longitudinal motion and ring breathing is still far in excess of the quantum result. 

In this paper we report MD investigations of coherent fluid motion in a system we have previously simulated, namely heliiun inside a carbon nanotube. It is argued that MD simulation is unsuitable for studying such phenomena. 

The polyethylene system, a loosely connected bond network, was chosen as a worst possible case in order to illustrate the limitations of classical MD simulation. Systems with external constraints (such as nearby chains in a crystal) or cyclical bond networks would be expected to exhibit significantly restricted motion. In fact, classical simulations of carbon nanotubes, which have a two-dimensional bond network, showed a sizeable but significantly smaller disagreement with quantum results. 

Water inside a carbon nanotube (CNT) shows another set of unusual features which have been the subjects ofgreat interest in recent years and are currently being studied extensively by experiments and simulations. A remarkable aspect unearthed is the ability of a CNT to act as water transporter and filter. The properties of water inside a CNT depend on the diameter d of the CNT, which is analogous to the parameter Wq of reverse micelles discussed in the preceding chapter. However, water within a single-wall CNT shows unusual features, such as single-file diffusion, the theory of which was developed in the past but a proper model system was lacking. The orientational motion of individual water molecules exhibits slow dynamics, quite different from those in the bulk. 

Hu,Y, Chen, W, Lu, L.H., Liu, J.H., Chang, C.R., 2010. Electromechanical actuation with controllable motion based on a single-waUed carbon nanotube and natural biopolymer composite. ACS Nano 4,... 

A stretchable carbon nanotube strain sensor for human-motion detection. Nat. Nanotechnol. 6, 296-301. 

Dielectrophoresis has also been used to manipulate macromolecules such as DNA, viruses, proteins, and carbon nanotubes. The term colloids will be used here to generally describe a particle between 1 and 1,000 nm. At this scale we need to take into consideration additional parameters that will affect the efficiency and application of dielectrophoresis. The first is Brownian motion, or the random chaotic movement of molecules, which will introduce another destabilizing variable if we were to trap colloids. Second, electrostatic effects at the surface of colloids, created by the electrical double layer, will influence particle-particle interactions. Factors such as hydrodynamic drag, buoyancy, electrothermal effects, and a particle s double layer interactions need to be considered when applying dielectrophoresis to colloids. 

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