pH-Dependent Foam Formation Using Amphoteric Colloidal Polymer Particles

Abstract

Near-monodispersed micrometer-sized polystyrene (PS) particles carrying amidino and carboxyl groups on their surfaces were synthesized by soap-free emulsion polymerization using an amphoteric free radical initiator. The resulting amphoteric PS particles were characterized in terms of diameter, morphology, disperibility in aqueous media and surface charge using scanning electron microscopy (SEM), optical microscopy (OM), sedimentation rate and electrophoretic measurements. At pH 2.0, where the amidino groups are protonated (positively charged), and at pH 11.0, where the carboxyl groups are deprotonated (negatively charged), the PS particles were well dispersed in aqueous media via electrostatic repulsion. At pH 4.8, where the surface charges are neutral, the PS particles were weakly aggregated. Furthermore, it was confirmed that the PS particles can function as a pH-sensitive foam stabilizer: foamability and foam stability were higher at pH 2.0 and 4.8, where the PS particles can be adsorbed to the air–water interface, and lower at pH 11.0, where the PS particles tend to disperse in bulk aqueous medium. SEM and OM studies indicated that hexagonally close-packed arrays of PS particles were formed on the bubble surfaces and moiré patterns were observed on the dried foams. Moreover, the fragments of dried foams showed iridescent character under white light.

Enhanced Stable Cavitation and Nonlinear Acoustic Properties of Poly(butyl cyanoacrylate) Polymeric Microbubbles after Bioconjugation

“…Plain PBCA MB showed values of −30 mV, consistent with previous publications. , After the hydrolysis step, the MB zeta potential slightly changed up to −23 mV, likely caused by the storage conditions of Hydro MB, as the pH of the storage solution was more acidic (pH 4.5) in order to prevent further (and uncontrolled) hydrolysis. The more acidic pH favors carboxylic protonation, which results in lower surface charges. , After streptavidin coupling, the resulting Strepta MB were almost neutrally charged (−4 mV), as we neutralized the pH of the storage solution postconjugation, and the resulting pH (7.4) was close to the isoelectric point of the streptavidin (6.0–7.5). − …”

“…The more acidic pH favors carboxylic protonation, which results in lower surface charges. 33,34 After streptavidin coupling, the resulting Strepta MB were almost neutrally charged (−4 mV), as we neutralized the pH of the storage solution postconjugation, and the resulting pH (7.4) was close to the isoelectric point of the streptavidin (6.0−7.5). 35−37 We evaluated the MB diameter using a Coulter counter, dynamic light scattering (DLS), and scanning electron cryomicroscopy (cryoSEM) (Figure 2b).…”