A statistical analysis of the first stages of freezing and melting of Lennard-Jones particles: Number and size distributions of transient nuclei.

The freezing/melting transition is at the heart of many natural and industrial processes. In the classical picture, the transition proceeds via the nucleation of the new phase, which has to overcome a barrier associated with the free energy cost of the growing nucleus. The total nucleation rate is also influenced by a kinetic factor, which somehow depends on the number of attempts to create a nucleus, that translates into a significant density of proto-nuclei in the system.

A Multi-Scale Study of Water Dynamics under Confinement, Exploiting Numerical Simulations in Relation to NMR Relaxometry, PGSE and NMR Micro-Imaging Experiments: An Application to the Clay/Water Interface.

Water mobility within the porous network of dense clay sediments was investigated over a broad dynamical range by using H nuclear magnetic resonance spectroscopy. Multi-quanta H NMR spectroscopy and relaxation measurements were first performed to identify the contributions of the various relaxation mechanisms monitoring the time evolution of the nuclear magnetisation of the confined heavy water. Secondly, multi-quanta spin-locking NMR relaxation measurements were then performed over a broad frequency domain, probing the mobility of the confined water molecules on a time-scale varying between microseconds and milliseconds.

Water Mobility within Compacted Clay Samples: Multi-Scale Analysis Exploiting H NMR Pulsed Gradient Spin Echo and Magnetic Resonance Imaging of Water Density Profiles.

H NMR pulsed gradient spin echo attenuation and water density profile analysis by magnetic resonance imaging are both used to determine the mobility of water molecules confined within a porous network of compacted kaolinite clay sample (total porosity of ∼50%). These two complementary experimental procedures efficiently probe molecular diffusion within time scales varying between milliseconds and few hours, filling the gap between the time scale of diffusion dynamics measured by traditional quasi elastic neutron scattering and through-diffusion methods. Furthermore, magnetic resonance imaging is a nondestructive investigation tool that is able to assess the effect of the local structure on the macroscopic mobility of the diffusing probe.

Ionic association analysis of LiTDI, LiFSI and LiPF in EC/DMC for better Li-ion battery performances.

New lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole-1-ide (LiTDI) are now challenging lithium hexafluorophosphate (LiPF), the most used electrolyte salt in commercial Li-ion batteries. Thus it is now important to establish a comparison of these electrolyte components in a standard solvent mixture of ethylene carbonate and dimethyl carbonate (EC/DMC: 50/50 wt%). With this aim, transport properties, such as the ionic conductivity, viscosity and Li self-diffusion coefficient have been deeply investigated.

New approach for understanding experimental NMR relaxivity properties of magnetic nanoparticles: focus on cobalt ferrite.

Relaxivities r and r of cobalt ferrite magnetic nanoparticles (MNPs) have been investigated in the aim of improving the models of NMR relaxation induced by magnetic nanoparticles. On one hand a large set of relaxivity data has been collected for cobalt ferrite MNP dispersions. On the other hand the relaxivity has been calculated for dispersions of cobalt ferrite MNPs with size ranging from 5 to 13 nm, without using any fitting procedure.

Transport properties investigation of aqueous protic ionic liquid solutions through conductivity, viscosity, and NMR self-diffusion measurements.

We present a study on the transport properties through conductivity (σ), viscosity (η), and self-diffusion coefficient (D) measurements of two pure protic ionic liquids--pyrrolidinium hydrogen sulfate, [Pyrr][HSO(4)], and pyrrolidinium trifluoroacetate, [Pyrr][CF(3)COO]--and their mixtures with water over the whole composition range at 298.15 K and atmospheric pressure. Based on these experimental results, transport mobilities of ions have been then investigated in each case through the Stokes-Einstein equation.

Anisotropic porous structure of pharmaceutical compacts evaluated by PGSTE-NMR in relation to mechanical property anisotropy.

Purpose: The pore space anisotropy of pharmaceutical compacts was evaluated in relation to the mechanical property anisotropy.

Methods: The topology and the pore space anisotropy were characterized by PGSTE-NMR measurements. Parallelepipedical compacts of anhydrous calcium phosphate (aCP) and microcrystalline cellulose (MCC) were tested on top, bottom and side faces.

Orientational microdynamics and magnetic-field-induced ordering of clay platelets detected by 2H NMR spectroscopy.

The orientation of montmorillonite clays induced by a static magnetic field is quantified by using (2)H NMR spectroscopy. Indeed, the residual quadrupolar splitting of the (2)H resonance line measured for heavy water is a direct consequence of the specific orientation of the clay platelets in the static magnetic field. In the dilute regime, this residual splitting increases linearly with clay concentration, which confirms that the clay/clay electrostatic repulsions remain negligible by comparison with the diamagnetic coupling of these anisotropic platelets.

Application of PGSTE-NMR technique to characterize the porous structure of pharmaceutical tablets.

Direct compaction of pharmaceutical tablets is a complex process that results in a heterogeneous density distribution inside the compact. In the present study, we have used a non-invasive and non-destructive technique: the pulsed-gradient stimulated-echo (PGSTE) NMR method to access to topological information (connectivity, tortuosity) about the porous structure of the tablets obtained with three different pharmaceutical excipients: the microcrystalline cellulose, the lactose and the anhydrous calcium phosphate. These materials were chosen since their mechanical properties under pressure are highly differentiated.

Anomalous diffusion of water in [BMIM][TFSI] room-temperature ionic liquid.

We have studied the self-diffusion properties of butyl-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([BMIM][TFSI]) + water system. The self-diffusion coefficients of cations, anions, and water molecules were determined by pulsed field gradient NMR. These measures were performed with increased water quantity up to saturation (from 0.

Application of percolation model to the tensile strength and the reduced modulus of elasticity of three compacted pharmaceutical excipients.

Percolation theory has been applied to several mechanical properties of pharmaceutical tablets. This power law describes the change of tablet's properties with the relative density. It defines critical tablet densities from which the mechanical properties start to change.

Analysis of the degree of nematic ordering within dense aqueous dispersions of charged anisotropic colloids by 23Na NMR spectroscopy.

Aqueous dispersions of Laponite, a synthetic clay neutralized by sodium counterions, are used as a model of charged anisotropic colloids to probe the influence of the shape of the particle on their organization within a macroscopic nematic phase. Because of the large fraction of condensed sodium counterions in the vicinity of the clay particle, (23)Na NMR is a sensitive probe of the nematic ordering of the clay dispersions. We used line shape analysis of the (23)Na NMR spectra and measurements of the Hahn echo attenuation to quantify the degree of alignment of the individual clay particles along a single nematic director.

Study of the casting of sulfonated polyimide ionomer membranes: structural evolution and influence on transport properties.

A casting process has been studied for charged polymers: the sulfonated polyimide ionomer membrane. The formation of the membrane has been followed by X-ray reflectivity as a function of temperature. The effect of equivalent weight has been also investigated.

Quantitative measurements of localized density variations in cylindrical tablets using X-ray microtomography.

Direct compaction is a complex process that results in a density distribution inside the tablets which is often heterogeneous. Therefore, the density variations may affect the compact properties. A quantitative analysis of this phenomenon is still lacking.

Quadrupolar interaction study of various cations confined in porous charged polymer film of sPI ionomers.

The structure of a sulfonated polyimide (sPI) ionomer membranes was investigated via the transport properties of various confined cations (7Li+, 23Na+, 87Rb+, 133Cs+). Their NMR spectra show large residual quadrupolar splitting depending on the orientation of the film in the static magnetic field B0. This behavior is the fingerprint of a macroscopic nematic ordering of charged interfaces.