  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.
