Confinement effects in ionomers: a high-field pulsed electron spin resonance spectroscopy study

Confinement effects in ionomeric poly(isoprene) homopolymers and poly(styrene)-poly(isoprene) diblock copolymers have been studied by pulsed high-field electron spin resonance spectroscopy. The reorientation of paramagnetic tracers (spin probes) being localized at the interface between the ionic clusters and the polymer has clear uniaxial features. Evidence is given that the dynamical constraints on the poly(isoprene) chains in the diblock copolymer propagate over the whole chain consisting of approximately 170 monomer units or over distances of several nano-meters. (C) 2002 Elsevier Science B.V. All rights reserved

Electron spin relaxation due to small-angle motion: Theory for the canonical orientations and application to hierarchic cage dynamics in ionomers

Analytical expressions for transverse electron spin relaxation induced by small angle motion were derived for the first time within an anisotropic model for rotational diffusion by using an approximation of the spin Hamiltonian and its variation during reorientation that is valid close to the canonical orientations. The dependence of the decay of the stimulated echo on such motion was studied by extensive Monte Carlo simulations and regimes were identified in which the time constant of this decay is related to parameters of the anisotropic diffusion model by simple equations. For testing these theoretical findings and obtaining insight into hierarchical cage dynamics in soft matter, high-field electron paramagnetic resonance (EPR) measurements were performed at a frequency of 94 GHz where the canonical orientations for nitroxide spin labels are well resolved. A combination of continuous wave EPR, saturation recovery measurements, and measurements of the decay of primary and stimulated electron spin echoes was employed to cover time scales from a few picoseconds up to several microseconds. Ionic spin probes attached by electrostatic interactions to the surface of ionic clusters in ionomers were used as a model system in which slow cage reorientation can be studied in the glass transition region of the polymer (0.64<T/T-g<1.05). Three hierarchical reorientation processes of the spin probe were observed on different time scales. The spin probe undergoes fast intramolecular libration on the time scale of a few picoseconds, it experiences a local rearrangement of the cage on the time scale of hundreds of nanoseconds and it performs cooperative reorientation coupled to the structural relaxation of the glassy matrix over time scales comparable to or longer than several microseconds in the glass transition region. (C) 2003 American Institute of Physics

Carbon nanotubes

International audienceCarbon nanotubes (CNT s) are remarkable objects that once looked set to revolutionize the technological landscape in the near future. Since the 1990s and for twenty years thereafter, it was repeatedly claimed that tomorrow's society would be shaped by nanotube applications, just as silicon-based technologies dominate society today. Space elevators tethered by the strongest of cables, hydrogen-powered vehicles, artificial muscles: these were just a few of the technological marvels that we were told would be made possible by the science of carbon nanotubes. Of course, this prediction is still some way from becoming reality; most often the possibilities and potential have been evaluated, but actual technological development is facing the unforgiving rule that drives the transfer of a new material or a new device to market: profitability. New materials, even more so for nanomaterials, no matter how wonderful they are, have to be cheap to produce, constant in quality, easy to handle, and nontoxic. Those are the conditions for an industry to accept a change in its production lines to make them nanocompatible. Consider the example of fullerenes – molecules closely related to nanotubes. The anticipation that surrounded these molecules, first reported in 1985, resulted in the bestowment of a Nobel Prize for their discovery in 1996. However, two decades later, very few fullerene applications have reached the market, suggesting that similarly enthusiastic predictions about nanotubes should be approached with caution, and so should it be with graphene, another member of the carbon nanoform family which joined the game in 2004, again acknowledged by a Nobel Prize in 2010. There is no denying, however, that the expectations surrounding carbon nanotubes are still high, because of specificities that make them special compared to fullerenes and graphene: their easiness of production, their dual molecule/nano-object nature, their unique aspect ratio, their robustness, the ability of their electronic structure to be given a gap, and their wide typology etc. Therefore, carbon nanotubes may provide the building blocks for further technological progress, enhancing our standard of living. In this chapter, we first describe the structures, syntheses, growth mechanisms, and properties of carbon nanotubes. Then we introduce nanotube-based materials, which comprise on the one hand those formed by reactions and associations of all-carbon nanotubes with foreign atoms, molecules and compounds, and on the other hand, composites, obtained by incorporating carbon nanotubes in various matrices. Finally, we will provide a list of applications currently on the market, while skipping the potentially endless and speculative list of possible applications

Carbon nanotubes

Carbon nanotubes (CNTs) are remarkable objects that once looked set to revolutionize the technological landscape in the near future. Since the 1990s and for twenty years thereafter, it was repeatedly claimed that tomorrow’s society would be shaped by nanotube applications, just as silicon-based technologies dominate society today. Space elevators tethered by the strongest of cables, hydrogen-powered vehicles, artificial muscles: these were just a few of the technological marvels that we were told would be made possible by the science of carbon nanotubes. Of course, this prediction is still some way from becoming reality; most often the possibilities and potential have been evaluated, but actual technological development is facing the unforgiving rule that drives the transfer of a new material or a new device to market: profitability. New materials, even more so for nanomaterials, no matter how wonderful they are, have to be cheap to produce, constant in quality, easy to handle, and nontoxic. Those are the conditions for an industry to accept a change in its production lines to make them nanocompatible. Consider the example of fullerenes – molecules closely related to nanotubes. The anticipation that surrounded these molecules, first reported in 1985, resulted in the bestowment of a Nobel Prize for their discovery in 1996. However, two decades later, very few fullerene applications have reached the market, suggesting that similarly enthusiastic predictions about nanotubes should be approached with caution, and so should it be with graphene, another member of the carbon nanoform family which joined the game in 2004, again acknowledged by a Nobel Prize in 2010. There is no denying, however, that the expectations surrounding carbon nanotubes are still high, because of specificities that make them special compared to fullerenes and graphene: their easiness of production, their dual molecule/nano-object nature, their unique aspect ratio, their robustness, the ability of their electronic structure to be given a gap, and their wide typology etc. Therefore, carbon nanotubes may provide the building blocks for further technological progress, enhancing our standard of living. In this chapter, we first describe the structures, syntheses, growth mechanisms, and properties of carbon nanotubes. Then we introduce nanotube-based materials, which comprise on the one hand those formed by reactions and associations of all carbon nanotubes with foreign atoms, molecules and compounds, and on the other hand, composites, obtained by incorporating carbon nanotubes in various matrices. Finally, we will provide a list of applications currently on the market, while skipping the potentially endless and speculative list of possible applications