Ultrasound-assisted synthesis of oil-in-water nanoemulsions: stability and rheological characteristics

Abstract

A stable neem oil-based oil-in-water nanoemulsion (o/w NE) is obtained by using a series of combinations of low and high-energy methods using optimized emulsifier composition. The application of the ultrasonication (high-energy) along with the dilution (low-energy) methods was used to intensify the process. Azadirachtin (indigenous neem oil) is used as an oil phase along with a mixture of two nonionic surfactants, namely Span80 and Tween80. The o/w NE is synthesized at an optimized HLB value of 8.5. Process parameters of ultrasonication are optimized and resulted in a 25% amplitude ratio, a 0.5 pulse mode factor, and a 30 minutes of ultrasonication time. The effects of optimized parameters are studied on droplet size distribution and the stability of o/w NE. For the oil concentration of 2.5%, the droplet diameter changed from 159 to 160.9 nm for a period of 45 days. Rheological properties of NEs are also evaluated by studying the relationship between shear rate with shear stress and viscosity at different temperatures, ranging from 20 to 50 °C. All the synthesized o/w NEs showed Newtonian behavior. Hence, the o/w NEs exhibited excellent stability for 45 days in terms of its droplet size, appearance, and rheology. The proposed o/w NE could be a potential pesticide for safeguarding the crops, without affecting the useful microorganisms, in the agriculture fields.

Graphical Abstract

Keywords:

• Nanoemulsions
• oil-in-water emulsions
• rheology
• stability
• ostwald ripening

Acknowledgments

Authors Diksha Vats acknowledges the financial assistantship provided by the Ministry of Education, Government of India in completing this work.

Additional information

Funding

This study was funded by Ministry of Education, Government of India.