Research on optimizing focused ultrasonic parameters for Surfactant-Free nanoemulsion with prolonged stability

Stable-state emulsions with no phase separation and dispersed-particle aggregation can be utilized in various fields, such as cosmetics, pharmaceuticals, food, and drug delivery. However, the physicochemical properties and stability of emulsions are significantly affected by factors such as concentration, mixing method, droplet size, and temperature. Surfactants (emulsifiers), which are used to form stable emulsions, adversely affect the human body and environment and influence the properties of emulsions, thereby limiting their development. This study manufactured stable emulsions without a surfactant using ultrasonic equipment. The oil particle size distributions, zeta potentials, microscopic observations, and emulsion stabilities of six emulsions (with an oil content of 1 %) prepared using different frequencies (250–1000 kHz) and output powers (50–150 W) were analyzed, immediately after preparation at 25 °C and 3 d thereafter. Finally, it was possible to manufacture a stable emulsion without particle size change or phase separation with a particle size in the 100 nm range and a surface charge value of −40 mV or more under conditions of 400 kHz and 150 W. This study proposed a method (with the optimum conditions) for manufacturing surfactant-free emulsions by analyzing the stability of emulsions manufactured under various frequencies and output-power conditions. The proposed method could open new frontiers in emulsion development and applications.