Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

Abstract

This paper presents a small-angle X-ray scattering (SAXS) characterization of the structural organization of deposits of Fe-montmorillonite dispersions formed during frontal ultrafiltration in a magnetic field. The mineral colloidal dispersions are made up of platelike montmorillonite clay particles with average thickness and diameter of about 2 and 500 nm, respectively. A newly developed X-ray-compatible frontal ultrafiltration cell allowed simultaneously applying a transmembrane pressure (5 × 104 Pa) and a magnetic field. The Fe-montmorillonite dispersions obtained by cation exchange reaction displayed regular ordering of the particles with an anisotropic arrangement when subjected to a uniform magnetic field of strengths ranging up to 1.4 T. The degree of anisotropy and the particle concentration profiles as a function of the distance from the filter membrane were deduced from the measured SAXS intensity. For the same volume of filtered permeate (0.26 mL), the deposit formed in a magnetic field of 1 T exhibits an anisotropic arrangement of the platelike particles with their faces aligned parallel to the membrane. In the absence of a magnetic field, the deposits are composed of randomly oriented particles. The application of an external magnetic field produced uniaxially oriented deposits with a higher concentration of particles, and resulted in a higher permeation flow than in the absence of the field.

Magneto-orientational properties of ionically stabilized aqueous dispersions of Ni(OH)2 nanoplatelets

“…Substituting in equation 2the obtained SAXS results, one obtains for the mean value of the intrinsic anisotropy the estimate δn o = −0.05 ± 0.005. We note that the field-induced orientation reported here is essentially different from the one obtained in [15,16], where the platelets positioned their flat faces parallel to the field. The explanation is that the mineral microdisks in [16] are diamagnetic; hence, due to the shape effect, their field-induced dipoles align with the major dimension of the object.…”

“…In some aspect, the effects encountered are similar to those reported for lyotropic colloids of mineral particles: goethite nanorods [14], Fe-montmorillonite [15] or gibbsite [16,17]. However, the orientational ordering that takes place in nickel hydroxide nanodispersions is significantly different: under a magnetic field the platelets orient their planes perpendicular to the direction of the latter as if they were striving to build up a diskotic nematic phase.…”

Structure and rheological behavior of casein micelle suspensions during ultrafiltration process

“…During the past decade there are several experiments 1-3 and theoretical models 4 -6 reported. [6][7][8][9][10][11][12][13][14] Previous work 15,16 concerning the microfiltration of skimmed milk showed that the transition from stable filtration to unstable condition is mainly governed by the formation of a deposit on the membrane. [7][8][9][10][11][12] Optimizing such processes require a better understanding of the mechanisms of deposit formation.…”

“…[7][8][9][10][11][12] Furthermore, in order to assess the filtration performance and to elucidate the limits of the stability zone, the structural properties of the a͒ Author to whom correspondence should be addressed. The structure of the suspensions may be considerably modified by the physicochemical as well as the hydrodynamic interactions during the separation process.…”

Structure, Rheological Behavior, and in Situ Local Flow Fields of Cellulose Nanocrystal Dispersions during Cross-Flow Ultrafiltration

“…Second, some studies tried to reveal the formation of concentrated layers at nanometer length scale using in situ and ex situ measurements: as an example in situ or ex situ small-angle neutron scattering (SANS) measurements − or a combination of static light scattering (SLS), SANS, and local birefringence techniques . More recently ultrafiltration cells dedicated to small-angle X-ray scattering (SAXS) measurements have been developed in dead-end mode − or cross-flow mode (coupled or not to ultrasound). − This equipment allowed getting access to the spatial and temporal in situ structural organization and concentration profile evolutions during ultrafiltration of colloidal suspensions.…”