Chen, Yijun (2020-03). Porous Nanofibers as the Host for Encapsulation and Tunable Release of Functional Material and Structural Energy Storage. Doctoral Dissertation.
Thesis
Encapsulating functional materials inside fibrous structures with the ability to dispense them on demand is an enabling technology that can open new frontiers in developing multifunctional composites and smart textiles. Conventional encapsulation techniques include simultaneous processing of the filler and the fiber (such as co-axial electrospinning and blend electrospinning). These methods often suffer from limited material choices, imposed by the strict material and processing compatibility requirements, and limited dose of the functional material. In this work, we have investigated the utilization of porous fibers as a platform to store functional materials and energy (ions) and release them on demand. The work has been carried out in two phases. First, we have established a broadly applicable porous fiber encapsulation technique based on sequential processing. In this method, electrically nonconductive or conductive porous fibers are fabricated, subsequently loaded with functional materials and encapsulated by a polymer coating in three different steps. Controllable passive release was demonstrated on non-conductive porous Poly(methyl methacrylate) (PMMA) fibers containing high mass loading of an antibacterial salt (Benzalkonium Chloride) encapsulated with sub-micron PMMA coating. In addition, activate release in response to an electric signal was demonstrated using conductive porous carbon nanofibers (CNF) yarns containing high mass loading of antibacterial material (Gentian Violet) encapsulated by a thin Polycaprolactone (PCL) coating. Active release of the functional material was achieved by heating up the yarn with Joule heating which facilitate the diffusion of the functional material through the PCL coating. The second phase of the project was with regards to the use of the porous fibers as structural energy storage platforms. Due to the excellent mechanical properties and the high specific surface area of the porous CNFs, they are also good candidate for multifunctional structural energy storage applications. The trade-off between energy storage and load bearing in porous CNFs was demonstrated for the first time by analyzing porous CNFs activated with KOH with different concentrations and activation temperatures. It was found that moderate activation can lead to dramatic improvement in capacitance(by >300%), at a rather moderate loss in strength(< 17%). The gain in specific surface area and capacitance in CNFs is many times those observed in bulk carbon structures, such as carbon fibers, indicating that activation is mainly effective near the free surfaces and for low-dimensional materials.
