Nematic ordering of suspension of charged anisotropic colloids detected by multinuclear quadrupolar spectra and 1H PGSE-NMR measurements
Centre de Recherche sur la Matière Divisée, UMR 6619 CNRS-Université d’Orléans, 45071 Orléans Cedex 2, France
* e-mail: firstname.lastname@example.org
Published online: 5 November 2003
The structure of aqueous dispersion of charged anisotropic nano-composites (synthetic Laponite clays) have been studied by NMR and numerical simulations based on a multi-scale statistical analysis have been used to interpret the mobility of the confined water molecule diffusing within dense Laponite aqueous dispersions (29–52% w/w) prepared by uniaxial compression. Firstly, the lineshape detected by NMR quadrupolar spectroscopy of the counterions (23Na or 7Li) exhibits a large residual splitting Δ ν which is the fingerprint of the macroscopic nematic ordering of the anisotropic particles. Secondly, these results are also confirmed by the anisotropy of the self-diffusion tensor of the water molecule measured by 1H Pulsed Gradient Spin Echo NMR. This self-diffusion anisotropy increases with the suspension density. Thirdly, the multi-scale statistical analysis of the water mobility bridges the gap between the time-scale (ps) accessible by Molecular Dynamics simulations and the time-scale (μs) accessible by Brownian Dynamics, leading to macroscopic behaviour comparable with PGSE-NMR data measurements.
PACS: codes. – 82.70.Dd - Colloids / codes. – 76.60.-k - Nuclear magnetic resonance and relaxation
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2003