Packing and voids in electro-rheological structures of polarized clay particles

TL;DR

This study investigates the meso-structural ordering of polarized fluorohectorite clay particles in oil suspensions under electric fields, revealing detailed 3D geometries and scattering behaviors of the resulting bundles using synchrotron SAXS.

Contribution

It provides the first quantitative analysis of the 3D internal structure of clay particle bundles formed under electric fields, linking SAXS data to pore and surface scattering characteristics.

Findings

Identification of anisotropic scattering patterns in clay bundles.

Quantitative determination of length scales within the bundles.

Differentiation between surface and bulk scattering contributions.

Abstract

Oil suspensions of fluorohectorite clay particles exhibit a dramatic meso-structural ordering when submitted to a strong electric field. This is due to dipolar interaction between polarized fluorohectorite particles, which orientate and aggregate to form chains and/or bundle-like structures along the direction of the applied electric field. We have used synchrotron small angle X-ray scattering to get insight into the nature of the porous medium in the bundles. Three types of fluorohectorite clay samples corresponding to three different intercalated cations Na+, Ni2+ and Fe3+ were studied. The two-dimensional SAXS images from bundles of fluorohectorites exhibit a marked anisotropy which is analyzed by fitting ellipses to iso-intensity lines of SAXS patterns. This also provides principal directions along which one-dimensional spectra are computed. They display a power law behavior typical of porous media, separated by crossovers. The crossovers are interpreted in terms of typical length scales for the clay particle bundles, providing for the first time a quantitative image of the 3D geometry inside such bundles of polarized clay particles. The exponents of the power laws indicate either predominant surface- (for 2 types of samples) or bulk- (for the last type) scattering, at all length scales investigated.