posted on 2024-01-04, 20:47authored byYanlin Guo, Xinpeng Zhang, Xiaohan Wang, Li Zhang, Zhenghe Xu, Dejun Sun
Ostwald
ripening, the dominant mechanism of droplet size growth
for an O/W nanoemulsion at high surfactant concentrations, depends
on micelles in the water phase and high aqueous solubility of oil,
especially for spontaneously formed nanoemulsions. In our study, O/W
nanoemulsions were formed spontaneously by mixing a water phase with
an oil phase containing fatty alcohol polyoxypropylene polyoxyethylene
ether (APE). By monitoring periodically the droplet size of the nanoemulsions
via dynamic light scattering, we demonstrated that the formed O/W
nanoemulsions are stable against Ostwald ripening, i.e., droplet growth.
In contrast, the nanoemulsion droplets grew with the addition of micelles,
demonstrating the pivotal role of the presence of micelles in the
water phase in the occurrence of Ostwald ripening. The influence of
the initial phase of APE, the oil or water phase in which APE is present,
on the micelle formation is discussed by the partition coefficient
and interfacial adsorption of APE between the oil and water phase
using a surface and interfacial tensiometer. In addition, the spontaneously
formed O/W nanoemulsion, which is stable against Ostwald ripening,
can be used as a nanocarrier for the delivery of water-insoluble pesticides.
These results provide a novel approach for the preparation of stable
nanoemulsions and contribute to elucidating the mechanism of instability
of nanoemulsions.