Microfluidic fabrication of colloidal/polymer-stabilized emulsions and colloidosomes

Abstract

Since microfluidics presented the micro-droplets world in a highly controllable way, droplet and related material technology have been pushed forward significantly in the last decades. With the enhanced ability to isolate single cell or molecule in one compartment and efficient performance of analytical reactions, microdroplets are appealing to bio/chemical assays. Moreover, research hotspots also extend to the functional materials derived from microdroplets, for the droplets are well-defined and versatile templates in fabricating of microparticles/microcapsules, polymersomes, vesicles, and customized microstructure assemblies. Owing to the microfluidic platform, those materials templated from microdroplets featured in controllable size, shape, architecture, and the response upon certain stimulus (temperature, UV, and so forth). They are great candidates in a wide range of applications including drug release systems, catalytic activities, optics, energy storage and pollution treatment and so on. This thesis focuses on the fabrication and characterization of colloidosome. Colloidosome is microcapsule with densely packed colloidal particles at surface. The colloidal particles endow colloidosome with significant flexibility with respect to its micro/nanostructure and the functionality. While colloidosomes are versatile capsules, some key challenge remains – they are intrinsicly leaky and brittle, and the fabrication process usually invovles toxic solvent. Therefore, explorations are made in designing biocompatible template for colloidosome, and formation process through novel formation mechanisms. In the part of smart colloidosome with temperaturely switched release profile, we first propose the biocopatible emulsion system and conduct synthesis of fluorosurfactant/nanopartices, and then the fast spreading mechanism of colloidosome formation has be revealed. The nanoparticles and thermal responsive polymer work synergeticly to present an on-demand release profile in such colloidosomes. In the study, 65% of the encapsulated fluorescence molecules are retained in the first 40 hrs with the existence of pluronic polymer in inner aqueous core, while the one without polymer will lose 68% of its fluorescence at the moment. Our experiments also figure out process parameters in regard to the microfluidic generation of double emulsions, and the impact of size discripancies on the release kinetics. On the other hand, nanofibers that can perform as a intertwined network are adopted in the TiO2 colloidosome part. In this design, colloidosomes with robust and versatile porous/hollow structures are produced from binary water/butanol system. Phase separation induced in mutual diffusion process generates differentiated evolutions of emulsion templates and thus varied final structure in colloidosomes. We further study the formation process of the spontaneously evolved O/W/O emulsion and the impact factors on surface morphology, porosity and final size of colloidosome. Our investigations bring out insights into the formation mechanisms and controlling parameters of novel microcapsules: those versatile systems open up new possibilities in producing tailor-designed functional materials. As microfluidics-based technique has great potential to be scaled up by the paralleled network, we will be able to witness the massive applications from encapsulation, controlled release expanding to catalytic host, energy storage, thermal therapy.