Spontaneous emulsification of toluene, xylenes, cyclohexane, and mineral oil in a nonionic nonylphenol polyethoxylate surfactant solution was investigated by visual observations coupled with dynamic light scatting measurements and interfacial tensiometry. For water-soluble oils, nanoscale emulsions formed spontaneously by diffusion of oil molecules into the aqueous surfactant solutions and subsequent swelling of surfactant micelles with oil. Micelle swelling rates were quantified to assess system spontaneity, revealing that oil solubility in water was directly correlated to the spontaneity of the emulsion (toluene > xylenes > cyclohexane). When experiments were intentionally designed to create surfactant concentration gradients, Marangoni flows were found to enhance spontaneity. Despite their spontaneous formation, emulsion stability was limited over the course of 40 days by Ostwald ripening followed by creaming and evaporation. These results provide insights on the likelihood of nanoemulsion formation and persistence in oily wastewater as the components in this study are present in many wastewater systems.

Spontaneous emulsification of toluene with nonylphenol polyethoxylate (NPE) and sodium dodecylbenzenesulfonate (SDBS) surfactants in saltwater environments was studied. NaCl promoted the spontaneous emulsification of an otherwise non-spontaneous SDBS−toluene system. Dynamic light scattering and turbidity indicated that spontaneity increased with NaCl concentration. The mechanism of spontaneous emulsification was dependent on surfactant type; NPE emulsified via micelle swelling, and SDBS emulsified via nucleation and growth. Hydrophilic lipophilic difference (HLD) calculations were used to model spontaneous emulsification and spontaneity. As HLD approached zero, conditions became more favorable for spontaneous emulsification. Between HLD values of −2.4 and −2.05, samples transitioned from non-spontaneous to spontaneous. This study aids in predicting spontaneous emulsion formation in saltwater environments for applications in nanoemulsion formation and wastewater remediation.

The impact of salts on the stability of oil-in-water emulsions to coalescence was studied to aid in minimizing the impact of emulsified oils on natural water systems. Oil-in-water emulsions were fabricated from mineral oil, deionized water, and sodium lauryl ether sulfate. As salt (NaCl) concentrations increased from 0 to 1.25 M, an increase in emulsion stability to coalescence was observed over an aging period of 56 days. ζ potential and interfacial tension measurements showed that salt decreased the electrostatic repulsion of the anionic surfactant and allowed the surfactant to pack more densely at the oil−water interface. Dynamic interfacial tension measurements showed that surfactant adsorption rates increased with salt. As a result of faster adsorption kinetics, oscillating droplet tensiometry showed a decrease in the dilatational modulus when salt was present. An extended DLVO theory was used to calculate the interaction energy between droplets. These calculations agreed well with our experimental results indicating the importance of hydration forces at high salt concentrations and small droplet separation distances. The presence of salt allowed for close surfactant packing and faster surfactant adsorption kinetics, which prevented coalescence and created conditions favorable for the formation of a stable Newton black film.

No abstract

In this study, we determined the accuracy and practicality of using optical microscopy (OM) and laser diffraction (LD) to characterize hydrogel particle morphology, size, and swelling capacity (Q). Inverse-suspension-polymerized polyacrylamide particles were used as a model system. OM and LD showed that the average particle diameter varied with the mixing speed during synthesis for the dry (10-120 lm) and hydrated (34-240 lm) particles. The LD volume and number mean diameters showed that a few large particles were responsible for the majority of the water absorption. Excess water present in the gravimetric swelling measurements led to larger Qs (8.2 6 0.37 g/g), whereas the volumetric measurements with OM and LD resulted in reduced capacities (6.5 6 3.8 and 5.7 6 3.9 g/g, respectively). Results from the individual particle swelling measurements with OM (5.2 6 0.66 g/g) statistically confirmed that the volumetric methods resulted in a reduced and more accurate measurement of the Q than the gravimetric method. V C 2017Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46055.

Spontaneous emulsion behavior has been difficult to predict and could be influenced by many variables including salinity, temperature, and chemical composition of the oil and surfactant. In this work, the hydrophilic–lipophilic difference (HLD) framework was used to predict the formation of spontaneous emulsions using a mixture of Span-80 and SLES surfactants. The spontaneity and emulsion behavior of different systems were modeled by estimating the HLDmix. The influence of surfactant ratio, salinity, and oil type was investigated. Spontaneous emulsification could only be observed when the HLDmix was between −0.96 and 1.04. Within this range, a negative HLDmix resulted in a greater spontaneity to form o/w emulsion, and a w/o emulsion was more likely to form when the HLDmix was positive. When the HLDmix was close to 0 (between −0.22 and 0.56 in our systems), emulsions were formed in both the oil and aqueous phases with high spontaneity. A combined effect of ultralow interfacial tension, Span-80 micelle swelling, and interfacial turbulence due to Marangoni effects is likely the main mechanism of the spontaneous emulsification observed in this study. A synergistic reduction in interfacial tension was observed between Span-80 and SLES (<1 mN/m). When the HLD of the system was close to 0, a bicontinuous emulsion phase was formed at the oil–water interface. The bicontinuous emulsion broke-up over time due to the ultralow interfacial tension and interfacial turbulence, forming dispersed oil and water droplets. Results from this work provide a practical method to suggest what surfactant composition, salinity, and oil type could promote (or eliminate) the conditions favorable for spontaneous emulsification.

No abstract

No abstract