Shell Formation Mechanism for Direct Microencapsulation of Nonequilibrium Pure Polyamine Droplet

• Published in: Journal of physical chemistry. C Vol. 123; no. 36; pp. 22413 - 22423
• Main Authors: Zhang, He, Zhang, Xin, Chong, Yong Bing, Peng, Junjie, Fang, Xinglei, Yan, Zhibin, Liu, Bin, Yang, Jinglei
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12.09.2019
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.9b06544

The understanding of the shell formation mechanism for the novel encapsulation technique via integrating microfluidic T-junction and interfacial polymerization is not only important to fabricate high-quality polyamine microcapsules but also of practical and theoretical significance to the wide application of this method based on nonequilibrium droplets. Herein, using pure polyamine as a targeting core, the shell formation mechanism was investigated by studying the achieved shell structures of the preliminary and final microcapsules and the behavior of nonequilibrium polyamine droplets in the coflow solvent. It reveals the shell has a multilayered structure, i.e., a rough outer layer, a porous middle layer, and a thin but dense inner layer, and the porous middle layer consists of pores with two size levels. This shell structure was correlated to fractal geometry of the polyamine droplet before being encapsulated, which was generated attributed to the interactions between the nonequilibrium polyamine droplet and the coflow solvent, i.e., interdiffusion and spontaneous emulsification. To achieve robust microcapsules, shell thickness and tightness were also studied by varying the composition of the reaction solution in terms of diisocyanate concentration and type of solvent with different polarity. The effect of these two key parameters on shell in this method is very similar to that in the traditional interfacial polymerization. In addition, the influence of the shell-forming stage and shell-growth stage on the robustness of microcapsule was discussed, indicating the former is decisive.