Deuterium Nuclear Magnetic Resonance Study of the Nematic Phase of Vanadium Pentoxide Aqueous Suspensions

Abstract

This article describes deuterium NMR experiments on nematic single domains of vanadium pentoxide suspensions in D 2 O. Despite V 2 O 5 volume fractions as low as 0.7%, the spectra are well-resolved quadrupolar doublets, characteristic of a uniaxial symmetry. We show that a simple model for the behavior of water in these suspensions accounts for the value of the splitting and for its concentration dependence. In this way, we obtain information on the interaction between water molecules and V 2 O 5 colloidal ribbons. Then, the solvent (D 2 O) is used as a probe to study the reorientation time of the nematic phase. We show that this technique is sensitive enough to distinguish between reorientation through a transient instability or through a homogeneous rotation. In this latter case, we measure the characteristic time of reorientation τ in a magnetic field, as a function of volume fraction and temperature. We show a very strong temperature dependence of τ, which contrasts with the athermal phase diagram of this system.

New Trends in Colloidal Liquid Crystals Based on Mineral Moieties

“…A recent 2 H nuclear magnetic resonance (NMR) study [41] of single domains of V 2 O 5 sols has shown that even at volume fractions as low as 0.7 %, water molecules still experience a residual anisotropic interaction due to a situation of fast exchange between the bulk and sites located on the surface of the ribbons. A recent 2 H nuclear magnetic resonance (NMR) study [41] of single domains of V 2 O 5 sols has shown that even at volume fractions as low as 0.7 %, water molecules still experience a residual anisotropic interaction due to a situation of fast exchange between the bulk and sites located on the surface of the ribbons.…”

Anisotropy of the Solvent Self-Diffusion Tensor as a Probe of Nematic Ordering within Dispersions of Nanocomposites

“…Nuclear magnetic resonance is a powerful tool to analyze the ordering of suspensions of anisotropic particles, such as liquid crystals [1][2][3], colloids [4,5], polymers [6], polyelectrolytes [7], and bilayers [8,9], if a sensitive nuclear probe is embedded within the particle or strongly linked to its surface [5,8,10]. In this article, we suggest the measurement of the solvent self-diffusion tensor anisotropy to quantify the ordering of nematic dispersions of anisotropic particles when such sensitive magnetic nuclei is lacking.…”

First Use of a Mineral Liquid Crystal for Measurement of Residual Dipolar Couplings of a Nonlabeled Biomolecule

“…The 2 H splitting of the bulk water due to the orientation of the MLC was 91 Hz, in agreement with ref. 14a.…”