Study the influence of various surfactants on the stability of oil-in-water emulsions by optical tweezers

Study on the stability of oil-in-water (O/W) emulsions is significant for breaking O/W emulsions, which is a key problem in oilfield wastewater treatment. So far, the traditional methods for exploring the stability of emulsions are mostly bulk measurements. Here, we report directly observing the sticking propability of pairs of emulsion droplets by optical tweezers to investigate the stability of O/W emulsions at the microscale. It was confirmed that resins in the oil phase and various types of surfactants in the aqueous phase are all beneficial for the stability of O/W emulsions. Besides, the conventional bulk measurements of Zeta potential and interfacial tension were also carried out to study the influence of the above species on the stability of O/W emulsions. The resultant data are well consistent with those obtained from the optical tweezer method (OTM). Our results show that optical tweezer is a new and reliable approach to evaluate the stability of oil-in-water emulsions and it opens up a bright road for exploring the stability of emulsions at microscale.