In Situ Characterization by SAXS of Concentration Polarization Layers during Cross-Flow Ultrafiltration of Laponite Dispersions

Abstract

The structural organization inside the concentration polarization layer during cross-flow membrane separation process of Laponite colloidal dispersions has been characterized for the first time by in situ time-resolved small-angle X-ray scattering (SAXS). Thanks to the development of new "SAXS cross-flow filtration cells", concentration profiles have been measured as a function of the distance z from the membrane surface with 50 μm accuracy and linked to the permeation flux, cross-flow, and transmembrane pressure registered simultaneously. Different rheological behaviors (thixotropic gel with a yield stress or shear thinning sol) have been explored by controlling the mutual interactions between the particles as a result on the addition of peptizer. The structural reversibility of the concentration polarization layer has been demonstrated being in agreement with permeation flux measurements. These observations were related to structure of the dispersions under flow and their osmotic pressure.

Mechanisms of flux decline in skim milk ultrafiltration: A review

“…This has only recently been made possible through the application of small angle X-ray scattering (SAXS). Early applications have allowed the monitoring of the evolution of concentration profiles near the membrane surface [107][108][109], however its resolution (especially at the membrane surface) has been limited by interferences from the membrane. SAXS has also been used to probe the behaviour of CMs near the membrane surface during filtration, which is discussed in the following section.…”

A strong and tough interpenetrating network hydrogel with ultrahigh compression resistance

“…The distance from sample to detector was 5015 mm and the X-ray wavelength was l ¼ 0.124 nm. The 2D SAXS data were converted to 1D intensity I(q) as a function of the scattering vector q [q ¼ (4p/l)sin q] by circular averaging, [26][27][28] where 2q is the scattering angle. Fully swollen hydrogels with a cut dimension of 50 Â 50 Â 1.0 mm 3 were used for SAXS analysis.…”

In situ microfluidic dialysis for biological small-angle X-ray scattering

“…Higher concentrations of protein may also introduce interesting non-Newtonian/rheological properties into the simulation. The formation of so-called polarization layers is a much-studied phenomenon in ultrafiltration that is closely related to this work (Song & Elimelech, 1995;Pignon et al, 2012). Transmembrane flow, which we have assumed constant in this work, can be impeded in the polarization layer by a variety of factors when protein solution becomes highly concentrated.…”

“…However, when expressed in units of mm H 2 O (10 Pa ' 1 mm H 2 O), it becomes evident that protein concentration and buffer exchange could be accomplished without PEG through the use of external pressure alone. Indeed, ultrafiltration has already been combined with SAXS measurements to probe the polarization layers in colloidal dispersions and micelles (David et al, 2008;Pignon et al, 2012). The extent to which behavior in those regimes applies to typical protein solutions should be a fruitful area for future investigation.…”