Modulation Mechanisms of Polymeric Emulsion Stability and Porous Material Architecture within Ultrasonic Fields

Ultrasonic emulsification has received great attention recently due to the great potential of tuning the emulsion droplets size compared to the traditional homogeneous mixing method. In this study, a series of polymeric emulsions were prepared by ultrasonic emulsification approaches. The relationships between ultrasonic power, emulsion destabilization mechanism and structure morphology of macroporous polymer material were studied. The water in toluene emulsion was prepared by mixing the polymer POSS-(PMMA)₈toluene solution (10 mg·mL^-1) and water or Na₂CO₃ aqueous solution (0.1 mol·L^-1) through different ultrasonic powers. The volume ratio of water/toluene was remained as 50:50. The evolution of emulsion droplets diameter distribution over time was analyzed based on optical microscopy data. The initial droplets diameter increased with the increase of ultrasonic power, and all emulsion droplets diameter distributions followed the diauxie curve. By changing the ion concentration in aqueous solution, excellent monodisperse emulsions with droplets diameter around 10 microns were acquired. It was found out that flocculation degree of emulsions prepared with Na₂CO₃ aqueous solution was increased with increasing of ultrasonic power. The relationship between ultrasonic power and emulsion stability was clarified by fitting the emulsion droplets diameter variation as the function of time. When ultrasonic power was below 750 W, Ostwald ripening dominated the instability mechanism of emulsion. Once the ultrasonic power achieved to 1000 W, the instability mechanism of emulsion was attributed to Ostwald ripening and coalescence at the same time. The macroporous polymer materials with adjustable pore diameter were prepared by dipping the glass fiber into salt containing emulsions. In this approach, POSS-(PMMA)₈ not only acted as emulsifier during emulsion preparation, but also treated as the skeleton of porous materials. The droplet-size of emulsions was monitored by changing ultrasonic power, meanwhile the structure and morphology of porous materials could be controlled on the basis of emulsion template.