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The discrimination induced by variable amplitude minipulses (DIVAM) filter can be tuned to select for signals from a particular domain, therefore it is possible to obtain signals specific to different domains using only one experiment. An early description of the DIVAM sequence, where the filter terminates with cross-polarization, explains this tune ability using a simple one-spin-relaxation model, thereby limiting the selection mechanism to incoherent processes. Recently, a more complete description of the selection behaviour was offered for the DIVAM filter, when it was directly applied to the observed nucleus (direct DIVAM), taking into account both the incoherent and coherent terms. Direct DIVAM experiments on poly(vinylidenefluoride) (PVDF) show significant phase distortions when large excitation angles were used. The signal from the amorphous domain is seen to nutate in a normal fashion with respect to the excitation angle, while those from the crystalline and defect units did not. The refocused DIVAM sequence is introduced to restore normal nutation for all signals. The selection behaviour is investigated using SIMPSON (simulation program for solid-state nuclear magnetic resonance (NMR) spectroscopy) simulations. These illustrate that the isotropic shift terms have been effectively removed and the dipolar term attenuated, such that the chemical shift anisotropy (CSA) leads to domain selection; however, in a different manner than seen in direct DIVAM. Therefore, this sequence provides a method to select on the basis of the CSA term in the presence of both strong dipolar couplings and a large range of isotropic shifts. Key words: nuclear magnetic resonance (NMR), polymer, domain selection, discrimination induced by variable amplitude minipulses (DIVAM), refocusing, spin dynamics, relaxation. Le filtre avec discrimination induite par des minipulsations d'amplitude variable (DIMAV) peut etre ajuste pour choisir des signaux a partir d'un domaine particulier; il est donc possible d'obtenir des signaux specifiques a differents domaines au cours d' une seule experience. Une description de la sequence DIMAV originale, dans laquelle le filtre se termine par une polarisation croisee, explique cette habilite a s'ajuster a l'aide d'un modele simple de relaxation a un spin, limitant ainsi le mecanisme de selection a des processus incoherents. Recemment, une description plus complete du comportement de selection a ete offerte pour le filtre avec des DIMAV qui, lorsquelle est directement appliquee au noyau observe (DIMAV directe), permet de tenir compte a la fois des termes coherents et incoherents. Des experiences de DIMAV directe sur du poly(fluorure de vinylidene) (PFPV) montrent qu'on observe des distorsions de phase importantes quand on utilise de grands angles d' excitation. On voit que, dans le mode normal, le signal du domaine amorphe subit une nutation par rapport al' angle d' excitation alors que ceux des unites cristallines ou defectueuses n' en subissent pas. On introduit la sequence de DIMAV refocalisee pour restaurer la nutation normale pour tous les signaux. On a etudie le comportement de selection par des simulations a l' aide du programme de simulation pour la spectroscopie resonance magnetique nucleaire (RMN) a l' etat solide (SIMPSON). Elles permettent d' illustrer que les termes de deplacement isotrope peuvent effectivement etre elimines et que le terme dipolaire peut etre attenue d' une facon telle que l' anisotropie du deplacement chimique (ADC) conduit a une selection du domaine; toutefois, cette selection est faite d'une facon differente de celle observee par une DIMAV directe. En consequence, cette sequence fournit une methode de selection sur la base du terme d'ADC en presence a la fois de forts couplages dipolaires et d' un large eventail de deplacements isotropes. Mots-cles : resonance magnetique nucleaire (RMN), polymere, selection d'un domaine, discrimination induite par des minipulsations d' amplitude variable (DIMAV), refocalisation, dynamique des spins, relaxation. [Traduit par la Redaction], Introduction Fluoropolymers see widespread commercial application, such as nonstick coatings (Teflon), textiles (GORE-TEX), and fuel cell membranes (Nafion). (1-3) Poly(vinylidenefluoride) (PVDF) is a semicrystalline fluoropolymer, which is exploited for its [...]

Author(s): Emily R. Cooper; Christopher D. Andrews; Paul S. Wheatley; Paul B. Webb; Philip Wormald; Russell E. Morris (corresponding author) The challenges associated with synthesizing porous materials [1] mean that [...]

The article demonstrates the applicability of the discrimination induced by variable-amplitude minipulse (DIVAM) experiment to obtain signals from different domains by using a spin dynamics analysis. The relaxation rate and the strength of the chemical shift anisotropy shift anisotropy shift anisotropy (CSA) interactions are used to set thed required direct DIVAM (DD).

Titanium oxides and carbides are often considered as electrode materials in energy conversion and storage devices due to their high potential conductivity and good stability. Titanium monoxide and titanium carbide have structures that can both be described as rocksalt with the same cubic close packed titanium sublattice with oxygen and carbon, respectively, occupying the octahedral interstices; however, the oxide is characterised by extensive defects on both sublattices whilst the carbide is stoichiometric and might be considered as an interstitial metal. Despite the anticipated very different natures of the oxide and carbide sublattices, these two phases actually form a complete solid solution. In the present investigation, we carefully characterise this titanium oxycarbide solid solution, reporting on the crystal structure, magnetic and electronic conduction properties. Titanium oxycarbide powders (TiO1−xCx with x = 0 ≤x≤ 1) have been prepared by solid state reactions of TiO and TiC powder under controlled environments at elevated temperatures. X-ray diffraction and pycnometric density measurements illustrate the gradual transition of the crystal structure of titanium oxycarbides from a vacancy containing rock-salt structure of TiO to fully occupied TiC with increase in carbon content in the oxycarbide lattice. The variation of the lattice parameter of the oxycarbide crystal as a function of the carbon content has been found to be non-linear which can be attributed to variations in the level of vacancies present in metal as well as non-metal sub-lattices. The existence of a short-range ordering of anion vacancies in oxycarbide with a nominal composition of TiO0.5C0.5 where half of oxygen of TiO is replaced by carbon has been confirmed by selected-area electron diffraction studies. Low temperature magnetic and conductivity measurements confirm that all oxycarbide compositions are Pauli paramagnetic and good metallic conductors. [ABSTRACT FROM AUTHOR]

The solid-state 13C spectra of poly(vinylidenefluoride)(PVDF) acquired by direct polarization (DP) with and without simultaneous 19F and 1H decoupling, under moderate sample spinningconditions, are compared to the spectra obtained using direct polarizationfollowed by a short Hahn echo. We show that by using an appropriatecombination of saturation and dephasing conditions high-resolutionsolid-state 13C NMR spectra of the amorphous domain canbe obtained. These spectra allow for a complete assignment of thesolid-state 13C NMR spectra of the amorphous phase of PVDF,and we propose a simple methodology to obtain high-resolution solid-state 13C NMR spectra of high molecular weight polymers. Furthermore,these spectra lead to the conclusion that differential line broadeningis occurring in the multiplet structure of the signals present inthe coupled spectra. This can be attributed to relaxation interferenceeffects and further reduces the line width in the coupled spectra,allowing for the dramatically improved resolution. In addition, thisexplains the loss of resolution when decoupling is applied duringthe acquisition of the solid-state 13C spectra of PVDF. [ABSTRACT FROM AUTHOR]

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