Résumé:

X-ray- and neutron-diffraction investigations of iodine intercalated single-walled carbon nanotubes are reported. Charge transfer between nanotubes and iodine leads to the formation of I-n(-) species (mainly I-3(-) and I-5(-)) as shown by Raman spectroscopy. By combining x-ray and neutron experiments, we show that the I-n(-) species are mainly localized inside the tubes. By comparing the experimental diagrams to our calculations, we show that some I-n(-) species are also present in the channels in between three tubes inside the bundles. The intercalation process also increases the disorder of the two-dimensional triangular lattice leading to a broad distribution of the iodine-carbon distances. Well ordered single-walled nanotube bundles are recovered after dedoping.

Commentaires: 195415

Ref HAL: hal-00658005_v1
DOI: 10.1103/PhysRevB.63.100302
WoS: 000167402100004
Exporter : BibTex | endNote
21 Citations
Résumé:

We report on C-13 nuclear magnetic resonance from 10 up to 350 K on single wall carbon nanotubes. The magic angle spinning NMR spectrum shows one isotropic line at 126 ppm and the static spectrum a powder pattern typical for a curved graphene sheet. The T dependence of the spin-lattice relaxation rate T-1(-1) reveals an unusual phenomenon which could be explained by thermally activated small amplitude motion (SAM) of the nanotubes. If above 170 K, diffusion of twistons might be responsible for the local SAM of the C-13 sites, below this transition temperature frozen in twistons could appear with an orientational order of the nanotubes in the ropes.

Ref HAL: hal-00003060_v1
Ref Arxiv: cond-mat/0410279
DOI: 10.1021/jp0113073
WoS: 000172020200013
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
57 Citations
Résumé:

In order to study the viscoelastic properties of certain complex fluids which are described in terms of a multiconnected transient network we have developed a convenient model system composed of microemulsion droplets linked by telechelic polymers. The phase behavior of such systems has two characteristic features: a large monophasic region which consists of two sub-regions (a fluid sol phase and a viscoelastic gel phase) separated by a percolation line and a two phase region at low volume fraction with separation into a dilute sol phase and a concentrated gel phase. From the plausible origin of these features we expect them to be very similar in different systems. We describe here the phase behavior of four different systems we prepared in order to vary the time scale of the dynamical response of the transient network; they consist of the combination of two oil(decane) in water microemulsions differing by the stabilizing surfactant monolayer (Cetyl pyridinium chloride/octanol or TX100/TX35) and of two telechelic polymers which are end-grafted poly (ethylene oxide) chains, differing by the end-grafted hydrophobic aliphatic chains (C12H25 or C18H37).

Commentaires: April 9 2001

Ref HAL: hal-00003062_v1
Ref Arxiv: cond-mat/0410278
DOI: 10.1021/la000317c
WoS: 000165267300020
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
75 Citations
Résumé:

Step strain experiments and dynamic light scattering measurements are perfomed to characterize the dynamic behavior of an o/w droplet microemulsion into which is incorporated a telechelic polymer. At sufficient droplet and polymer concentrations, above the percolation threshold, the system is viscoelastic and its dynamic structure factor shows up two steps for the relaxation of concentration fluctuations: the fast one is dominated by the diffusion but the slower one is almost independent of the wave vector. The terminal time of the stress relaxation tR and the slow time of the dynamic structure factor tS are both presumably controlled by the residence time of a sticker in a droplet: consistently, tR and tS are of the same order, they both vanishes at the percolation threshold according to power laws but with different exponents. We discuss these features in terms of deviations at the transition, from the usual mean field description of the dynamics of transient networks.

Commentaires: mars 2000

Ref HAL: hal-00003063_v1
Ref Arxiv: cond-mat/0410292
DOI: 10.1021/jp990980d
WoS: 000082335700032
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
54 Citations
Résumé:

In this paper we examine the effective interactions introduced between the droplets of an oil in water microemulsion upon progressive addition of hydrophobically modified water soluble poly(ethylene oxide)-PEO using essentially small angle neutron scattering. To discuss the relative importance of decoration and bridging of the droplets we compare analogous samples with addition of a PEO grafted at both extremities with hydrophobic C12H 25 chains (PEO-2m) or addition of a PEO grafted at one extremity only with a C12H 25 chain (PEO-m). PEO-m or PEO-2m adsorb onto the droplets via their hydrophobic extremities and the droplets are found to retain their form and size upon addition of up to 40 hydrophobic C12H 25 chains per droplet. When the volume fraction of droplets is less than about 10%, the effective interactions introduced by PEO-m or PEO-2m are found to be very different: PEO-m introduces a repulsive interaction while PEO-2m introduces an effective attractive interaction. This attractive interaction leads to an associative phase separation in the range of low volume fraction when a sufficient amount of PEO-2m is added.