UV-triggered Encapsulation and Release by Multilayer Microcapsules.

Abstract

Nowadays, the development of externally stimuli responsive vesicles possessing novel functionalities is full of challenging for various potential applications. As a practical matter, ultraviolet (UV) light responsive vesicles are finding intensive interest, as their micro/nano-structures can be tuned remotely by UV lights without involving direct contact or interaction. The development of such highly UV responsive vesicle is of great importance, where sometimes light would be the only available stimulus to drive the systems. The mainly aim of this work was to design polyelectrolyte capsules with unique externally UV responsive properties by using layer-by-layer assembly technique, to develop their applications for cargo encapsulation and release, and to get a better understanding of underlying mechanism based on UV light triggered phenomena. Strategically, three kinds of UV sensitive chemical compounds, benzophenone, azobenzene and diazonium, were introduced into building blocks for capsule preparation. Different functionalities of these capsules were studied, and their potential applications were investigated. To get a better understanding on the topic and contents discussed, an introduction and a literature review were first presented. Then experimental section containing materials, methods and instruments was followed in Chapter 3. In Chapter 4, weak polyelectrolyte microcapsules containing benzophenone groups were prepared. Bezophenone related crosslinking showed a reliable and swift approach to tighten and stabilize the shells without losing their pH-responsive properties. Chapter 5 investigated the microcapsules containing azobenzene groups, which could be activated to form J aggregates and further to destroy the integrity of shells upon exposure to UV light. In Chapter 6, microcapsules were fabricated with diazo-resin containing diazonium groups, which showed the ability to seal the porous shells via photolysis between diazonium and paired nucleophilic groups. Finally, in Chapter 7, Dual-function complex microcapsules containing both azobenzene and diazonium groups were fabricated to achieve both encapsulation and release trigged by same externally UV stimulus.