![]() In Part 2 of this series, the authors presented a model to show that colloid-laden oil-water interfaces behave viscoelastically. At sufficiently high concentrations of particles, colloid-laden oil-water interfaces tend to exhibit non-Newtonian behavior. The authors have shown in the past that emulsion stability is controlled primarily by the concentration of particles adsorbed at the oil-water interface. Colloidal particles that are partially wetted by both the aqueous and the oleic phases are capable of effectively stabilizing emulsions. « lessįinely divided insoluble solid particles constitute an important class of emulsifying agents. Lastly, these events helped overcome energy barriers to induce particle adsorption. Acoustically detected cavitation events could originate in the bulk solvent and/or inside the emulsion droplets. There was no evidence of spontaneous more » adsorption of particles onto the oil-water interface without ultrasound, which suggests the presence of a stabilizing force. The detection of acoustic cavitation and the simultaneous analysis of structural data via USAXS demonstrated direct correlation between Pickering emulsion formation and cavitation events. In this study, the role of sonication in the formation of Pickering emulsions from amphiphilic gold nanoparticles was investigated using a new sample environment combining ultrasound delivery with ultra-small-angle X-ray scattering (USAXS) measurements. Yet, the process of emulsion sonication is rarely characterized in detail and acoustic conditions are largely determined by experimenter's personal experience. We report that sonication is one of the most commonly used methods to synthesize Pickering emulsions. The crude oil/water Pickering emulsions could be broken using alkali as a trigger, which suggests the potential utility for the recovery of crude oil. Compared to the crude oil, the corresponding Pickering emulsions showed excellent flowability at various shear rates. Interestingly, the string-like structures of nanogel aggregations were found in the aromatic hydrocarbons/water Pickering emulsions, which significantly enhanced the emulsion stability. In addition, the average diameter of oil drops was independent of sonication period in the range of 15–240 s. The average diameter of oil droplets was no longer decreasing with nanogel concentration more » increment above 1000 mg/L. A small amount of nanogels were sufficient for the formation of Pickering emulsions. The PAM nanogel-stabilized o/w Pickering emulsions were quickly demulsified in alkaline solutions whereas they showed markedly stability in brines and under acidic conditions. Nanogels with different crosslinking and charge degree were synthesized through suspension polymerization and characterized at various salinities and pH using dynamic light scattering (DLS) and scanning electron microscopy (SEM). Oil-in-water (o/w) Pickering emulsions stabilized by polyacrylamide (PAM) and poly(acrylamide-co-acrylic acid) nano-sized crosslinked polymeric particles (nanogels) under various conditions are described herein. Moreover, the nanoparticles prevent coalescence at high surface coverages by forming dense layers at individual interfaces, while the particle bridges straddling two interfaces were found more » at low surface coverages, which can also keep the droplets apart. Finally, this in turn reduces resistance force and facilitates coalescence. Substantial desorption of particles from the interface was triggered as the degree of ionization increases. Oppositely, the ionization compromises emulsion stability when the particle surface coverage is high. When the particle density on the droplet surface is relatively low, the increasing resistance forces at higher degrees of ionization can effectively prevent droplet coalescence. Through analyzing droplet dynamics, resistance force variation, and electric field, we discovered that the resistance is attributed to direct electrostatic repulsion, the image charge effect near the water–oil interface, and steric hindrance among extended polymers. The maximal resistance forces were measured to quantitatively discriminate the efficacy of particles in stabilizing emulsions at different degrees of ionization. The degree of ionization of the grafted polyelectrolytes was adjusted to capture the pH responsiveness. Using a steered molecular dynamics approach, a mechanistic study of forced coalescence was performed to probe the resistance between two particle-covered droplets. Electrostatic dissipative particle dynamics simulations were conducted to model the interactions between emulsion droplets stabilized by pH-sensitive polyelectrolyte-grafted nanoparticles. ![]()
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