Investigate For The Dual-core Double Emulsion Formation And Osmolarity-triggered Coalescence Of Encapsulated Droplets

Droplet microfluidic technology can produce nanoliter-scale microreactors, which use the droplets as carriers to conduct biochemical reaction. A key step for realizing the droplet as microreactor is that two or more droplets containing different compositions have to be triggered to coalesce. The unique core-shell structure of double emulsion can separate the inner cores from the outer environment, and effectively protect the inner components from being contaminated by the outer environment, which provides versatile platform for nanoliter-scale biochemical reaction. Moreover although there are lots of studies on the use of double emulsions as microcapsules, there is little research on the coalescence of the inner cores. Depending on this condition, the thesis will focus on the formation of double emulsions and osmolarity-triggered coalescence of inner cores, which has important significance for the further application of the double emulsions.Firstly, research actuality is reviewed, and the basic mechanism for the droplet forming is proposed,which includes the related theories of the instability of the static fluid column and the instability of the dynamic fluid interface. Combined with the characteristics of glass capillary microfluidic device, the main cause of the two droplet generation regimes, dripping and jetting, and the influence of non-dimensional parameters in droplet dynamics on the droplet formation are analyzed. The relationship between the droplet size and the critical capi llary number is established. The effects of the three-phase flow rate on the droplet size and the number of the inner cores are studied, which provides some theoretical guidance for the preparation of the appropriate size of the dual cores double emulsion droplets.Secondly, based on the theoretical analysis, single emulsion droplet generation model is established and simulated using phase field method. Comparing with the theoretical analysis, the factors of flow velocity, phase viscosity and surface tension coefficient are simulated to investigate their effects on the droplet size and frequency, which provide some guidance for the experimental study of double emulsions.Finally, two kinds of glass capillary microfluidic devices are designed and processed. After setting up experimental system, the effects of three phase flow rate on the double emulsion droplet size, shell thickness and number of inner cores are studied to verify the correctness of theoretical analysis. Based on the experimental study of the influence of three phase flow rate on the number of cores, the osmolarity-responsive dual-core double emulsions are fabricated, and the influence of osmolarity on the inner cores coalescence is discussed. In addition, the feasibility of this osmolarity-controlled core-coalescence microreactor for nanoliter-scale reactions is explored.