Indirect determination of zeta potential at high ionic strength: Specific application to semipermeable polymeric membranes

Abstract

a b s t r a c tThe understanding of membrane charge neutralization and diffuse layer compression at environmentally relevant ionic strengths is becoming increasingly important. In this work, the impact of high ionic strengths on membrane zeta potential was determined using a combination of streaming potential measurements and theoretical modeling. Streaming potential measurements were conducted on cellulose triacetate (CTA) and polyamide thin-film composite (TFC) membranes at ionic strengths within the operating limits of an electrokinetic analyzer. Zeta potential calculated from streaming potential was then extrapolated to environmentally relevant ionic strengths (0.05 to 1 M 1:1 electrolyte) using the Debye-Hückel and Helmholtz-Smoluchowski models. Extrapolated zeta potential values revealed that membrane charge neutralization and compression of the diffuse layer are limited by the size of the hydrated counter-ions, and full membrane charge neutralization, or even charge reversal, can not be achieved. The expected zeta potential of CTA membranes was similar to that of TFC membranes at high ionic strength, which has considerable implications in the comparison of membrane performance when treating brackish and saline feed waters. The methodologies developed in this work can help to better understand the contribution of electrostatic forces resulting from zeta potential to the sum of interfacial forces present at the membrane surface.

Evaluation of the transport parameters and physiochemical properties of forward osmosis membranes after treatment of produced water

“…The standard deviation for all streaming potential measurements was less than ±1.0 mV. Further information on the streaming potential measurements and the calculation of zeta potential can be found elsewhere [9,32,33]. The surface energy parameters and hydrophobicity of each membrane active layer were calculated from captive bubble contact angle measurements using a goniometer (Rame-Hart Inc., Mountain Lakes, NJ).…”

“…A reduction in electrostatic repulsion between the polymer chains can compact the already dense membrane active layer and decrease water and solute permeability. In a recent study [32] we have shown that increasing ionic strength at a membrane-solution interface can shield the membrane's charge density and reduce its zeta potential by nearly 75%. The irreversible sorption of divalent counterions within the polymer matrix can also exacerbate charge neutralization and de-swelling.…”

“…According to the Donnan theory, increasing presence or density of ionizable groups and electrokinetic phenomena in the polymer matrix can accentuate membrane de-swelling [42,43]. This could explain why the apparent compaction of TFC1's selective layer was greater than that of the CTA's; the CTA membrane has been described in recent literature as lacking an ionizable polymeric surface, while the ionizable characteristics of polyamide membranes are well know [32]. Hindered diffusion through the TFC active layer due to contaminant sorption and entrapment within the selective layer might also occur concurrently with membrane de-swelling.…”

Selecting analytical tools for characterization of polymersomes in aqueous solution

“…Thus, PB-PEO polymersomes are more prone to aggregation than polymersomes with a higher surface charge. As charges may be screened by the presence of ions (here due to 50 mM NaCl concentration in the buffer), the zeta potential (and potential aggregation) of polymersomes may be controlled to some extent 138 .…”

Evaluation of forward osmosis membrane performance and fouling during long-term osmotic membrane bioreactor study

“…Salt accumulation also increases the ionic strength of the wastewater, which may increase bacterial adhesion to the membrane [45] and change the membrane surface charge (zeta potential) [46]. Coday et al [46] demonstrated that increasing ionic strength reduced the negative charge of FO membranes, which can potentially affect membrane fouling propensity and the bidirectional diffusion of ionic constituents across the membrane [46][47][48].…”