Zeta potential of single and polymer-coated microbubbles using an adapted microelectrophoresis technique

Abstract

a b s t r a c tThe zeta potential of microbubbles, generated by injecting pressurised air into water and then releasing the pressure, was determined in the absence and presence of different polyacrylamides. Air was dissolved in either water or solutions of cationic, anionic, amphoteric or nonionic polymers at a constant pressure of four atmospheres. The charge of the bubbles at the shear-zeta plane was measured using a modified microelectrophoresis glass cell, held at a stationary level, at varying pH (2.0-12.0). Known practical problems with this technique were solved, and these solutions are described in detail. The anionic, amphoteric and nonionic polymers increased the negative charge of the bubbles, but the isoelectric point (iep) remained constant at about pH 2.0. Conversely, in the presence of the cationic polymer, the bubbles exhibited positive surface charges between pH 2.0 and 8.0 and an iep of pH 8.0. The results revealed the existence of an important interaction mechanism between air bubbles and polymeric macromolecules; neither this mechanism nor its practical implications have been reported in the literature to date, especially in the treatment of wastewater by flocculation followed by dissolved air flotation (DAF).

Hydrophobically-associating cationic polymers as micro-bubble surface modifiers in dissolved air flotation for cyanobacteria cell separation

“…Bubbles modified with CTAB and polyDADMAC resulted in positive bubbles with little variation in the magnitude of their zeta potentials at pH 7. This is in agreement with literature for CTAB (Yoon and Yordan, 1986); however, the study of the effect of various cationic polymers is limited to commercially available polymers (Oliveira and Rubio, 2011). With all synthesised polymers used in this work, positively charged bubbles were generated; however, the bubble zeta potential was observed to shift to less positive values with increases in a) polymer hydrophobic functionality and b) polymer molecular weight (Fig.…”

“…The positive bubble zeta potential measurements observed in this study (Fig. 3) and in other studies (Malley, 1995;Oliveira and Rubio, 2011) indicate polymer adsorption at the bubble surface. However, highly cationic polymers (specifically LC10-h and HC10-h) had surface tensions similar to that of pure water at 72 mN m À1 (Table 1) despite the hydrophobic functionality.…”

“…At pH 7, the zeta potential of a micro-bubble in water is approximately À25 to À60 mV (Oliveira and Rubio, 2011;Yang et al 2001), though the value can be altered depending on background ionic conditions (Oliveira and Rubio, 2011;Yang et al 2001). Bubbles modified with CTAB and polyDADMAC resulted in positive bubbles with little variation in the magnitude of their zeta potentials at pH 7.…”

“…It is acknowledged, however, that further complications can arise in modified-bubble measurements due to differing polymer concentrations on bubble surfaces in a single system; for example, Oliveira and Rubio (2011) observed that randomly measured bubbles do not carry the same charge in a given system. With respect to the toxicity of polymers in water treatment, it is generally accepted that the polymers with greater cationicity are more toxic (Bolto and Gregory, 2007).…”

“…Similar to influent particles and colloids, DAF microbubbles are negatively charged, likely due to asymmetric dipoles of water molecules at bubble gas liquid interfaces (Oliveira and Rubio, 2011). The manipulation of the bubble surface charge, as opposed to that of particles, has received attention as an alternative to coagulation-flocculation (Han et al 2006;Henderson et al 2009).…”