Microwave memory for surface tension of PEG aqueous solution

Recently, microwave irradiation has been widely used chemical processes, such as emulsification and polymerization. When interface between liquid-air or liquid-liquid exists in the process, surface tension and interfacial... [ view full abstract ]

Recently, microwave irradiation has been widely used chemical processes, such as emulsification and polymerization. When interface between liquid-air or liquid-liquid exists in the process, surface tension and interfacial tension are important properties in separation and mixing process of two immiscible liquids. Although property of interfacial behavior is usually manipulated by surfactant addition, in previous study, we found that interesting behavior under microwave irradiation for surface tension reduction of not only water droplet but also aqueous solution. To understand the mechanism of the reduction, the water droplet includes surfactant, and the stronger microwave memory for surface tension reduction was observed that that of pure water. According to the results from various type of solution, formation of nano-bubble or water molecule cluster was considered as one of the reasons. Although the length of surfactant might be important for the surface activating ability and the interfacial stability, quantitative estimation for different length has been still difficult in the case of surfactant. In this study, various types of polyethylene glycol (PEG), which is polyether compound and water-soluble, were added, and the surface tension was measured under microwave irradiation through changing the polymerization degree (polymer length) and the concentration. Surface tension profiles showed the importance of polymer length and the concentration to get specific surface tension reduction. For example, when same amount of polymer was added in the solution, polymer addition of shorter unit was effective for getting microwave memory. This is a reason that more units can be adsorbed at the liquid-air interface of bubbles, which are produced by the irradiation. Moreover, the microwave effect depended on the concentration, and more concentration caused the reduction. Accordingly, we thought that addition of short length polymer contributes stability of liquid-air interface of nano-bubbles. Finally, further surface tension reduction can be achieved by synergy effect of addition of shorter soluble polymer and microwave irradiation.