(337ci) Practical Application of Surface-Active Nanoparticles

Fluid-fluid interfaces have widespread industrial applications including foods, cosmetics, biosensing, lubricants, porous structures, drug delivery, coating, etc. In Pickering emulsions, solid particles stabilize the fluid-fluid interface, and their presence reduces the interfacial energy between the two fluids. In order to stabilize the oil/water interface with high efficiency, in my work, a type of amphiphilicity-adaptable graphene quantum dots (C-GQDs) was developed by a facile one-step bottom-up method. This fabricated C-GQDs could be used to stabilize the oil-in-water Pickering emulsion at an ultralow concentration, only 0.001%. Moreover, the emulsification ability of C-GQDs could be controlled by adjusting pH values in aqueous solution. And the demulsification- emulsification cycles could be repeated for 3 times. It made them have potential to apply in large-scale with cost effectiveness. For expanding the practical applications of amphiphilic graphene quantum dots, it is important to solve the instability issues of emulsifiers in harsh conditions, such as salty conditions. In order to solve this problem, I designed a type of zwitterionic graphene quantum dots (ZGQDs) by surface modification method. The ZGQDs could stabilize oil-in-water emulsion under seawater conditions. Moreover, the ZGQDs has dynamic interfacial assemble ability which made them have potential applied in controlled-release application.

The Pickering emulsion systems also have been used to template composite structures with improved functionalization, such as armored polymer particles and capsules. In order to introduce carbon-based nanomaterials into polymer matrix more efficiently to improve flame-retardant properties, I used surface-active GQDs to stabilize styrene-in-water Pickering emulsion as a template, and then do polymerization to give GQDs-armored particles with tunable flammability. The properties of prepared polymer composites could be tailored by controlling the nanoparticle concentration in aqueous phase. The prepared GQDs-armored particles showed improved thermal stability and flame-retardant properties. And the next, in order to solve the instability issue of adding ionic liquids (ILs) in a coating system, I used to encapsulation of ILs to solve this problem. These ILs encapsulated by silica shell were prepared by Pickering emulsion templated method. The prepared ILs capsules were used as additive in a coating system directly and it would not lead to this system unstable, and improve the flame retardancy as well. Finally, I used these surface-active GQDs to decorated the 2D materials to improve the interfacial affinity between the additives and polymer matrix. The polystyrene composites were fabricated by extrusion method, and they showed improved flame-retardant and mechanical properties with low loading (5 wt%) of additives.

In summary, my research work focused on the development of varied functionalized GQDs to investigate their collective interfacial behavior, and exploit them in diverse applications including encapsulation, controlled-release, and developing polymer nanocomposites with improved flame-retardant and mechanical properties.