| Nanoemulsions are kind of special soft material with droplet size from20to200nm, which are also referred to as miniemulsions, submicro-emulsions, translucent emulsions or unstable microemulsions. Due to the nano-scale droplet size, nanoemulsions have transparent or translucent appearance and most of the nanoemulsions have much higher stability against droplet aggregation, gravitational sedimentation or creaming than conventional emulsions. These desirable properties of nanoemulsions attract increasing attention both in fundamental studies and in practical applications (e.g. petroleum, foods, cosmetics, drugs, pesticides, and coating). However, most of publications and applications of nanoemulsions focus on O/W type. There are only a few publications related to W/O nanoemulsions generated by low-energy methods. The research in the preparation methods of W/O nanoemulsions was relatively scarce. W/O nanoemulsions have indispensable influence in some research fields, such as foods, drug delivery system, and nanometer material preparation. Therefore, the research in the preparation method and stability of W/O is of great theoretical and practical significance.Low-energy methods are kind of widely used methods in nanoemulsions preparation, which mainly include phase inversion temperature method (PIT), phase inversion composition method (PIC), microemulsions dilution method, Spontaneous emulsification method, dropwise addition method etc. Only phase inversion temperature method, phase inversion composition method and dropwise addition method were used in the preparation of W/O nanoemulsions. Additionally, the number of reported W/O nanoemulsions was less than ten. Moreover, highly stable concentrated W/O nanoemulsions have important applications in the actual production and life, such as pesticides, food cream and oil-base drilling fluid. However, there is no report about highly stable concentrated W/O nanoemulsions tillIn this thesis, aiming at the shortcomings of current research in the preparation method of W/O nanoemulsions and the deficiency of highly concentrated W/O nanoemulsions, we select two nonionic surfactants systems (Span80-Tween80and Span80-Brij35) as research object with the white oil (Marcol52) used as oil phase. W/O nanoemulsions and highly stable concentrated W/O nanoemulsions in two systems were prepared by low-energy methods. The thesis mainly includes two aspects as following.Firstly, W/O nanoemulsions in the system of water/Span80-Tween80/white oil were prepared by a new low-energy method (PIC method at elevated temperature). Additionally, we focus on the research in the influence factors of nanoemulsions droplet size and stability, such as surfactant-water-ratio, oil-water-ratio, the HLB of the surfactants ect.Secondly, in water/Span80-Brij35/white oil system, highly stable concentrated W/O nanoemulsions could be prepared by PIC method at elevated temperature. In this system, W/O macroemulsions with the droplet size of about50μm were obtained by PIC method at ambient temperature or directly mixing at room temperature. However, W/O nanoemulsions with the droplet size from70μm to200nm were formed by PIC method at80℃癈. The internal phase content of the emulsions could reach as high as60wt%and the nanoemulsions were stable without obvious change in droplet size in two months. Afterwards, we found the phenomena in experiment as follows. When water phase and surfactants oil solution were mixed at ambient temperature, we obtained W/O coarse emulsions. Then, heating the coarse emulsions to specific temperature, we can also obtain finely dispersed W/O nanoemulsions. We consider this simple low-energy method as thermal treatment. What’s more, the droplet size and stability of nanoemulsions obtained by thermal treatment were similar to nanomulsions formed by PIC method at80℃. Namely, we obtained highly concentrated W/O nanoemulsions by simple thermal treatment. At last, we conclude the emulsification mechanism of thermal treatment. |
PDF Full Text Request