|Institution:||University of Pennsylvania|
|Keywords:||composites; lightweight; mechanical properties; microfluidics; nanoparticle-shelled bubbles; nanostructure; Chemical Engineering; Mechanical Engineering; Mechanics of Materials|
|Full text PDF:||http://repository.upenn.edu/edissertations/1028
Lightweight materials that are mechanically robust are of great interest in automotive, aerospace, and construction industries. However due to the nature of materials, it is challenging to obtain materials that have high strength, stiffness and toughness, and light weight simultaneously. One approach that tries to address this limitation is the use of composite materials containing hollow microparticles, also known as syntactic foams. The incorporation of hollow microparticles decreases the density of the material at the same time that increases its specific strength. Conventional methods of fabrication of hollow particles involving bulk reactions result in high heterogeneity in geometry as well as mechanical properties, and little or no control over the shell nanostructure. This variability in the structure and properties of the hollow microparticles adversely affects the macroscopic properties of the syntactic foams and hinders the understanding of the structure-property relationship. The use of microfluidics for the generation of shelled-bubbles addresses these limitations. This microfluidic technique, in contrast to bulk methods, is based on single droplet formation, allowing for the generation of highly uniform bubbles, and enabling the assembly of nanoparticles at the interface forming stable nanoparticle-shelled bubbles. Microfluidics allow a precise control over the geometry, nanostructure and properties of the shelled-bubbles, further enabling the functionalization of the shell surface to present amphiphilicity, or the modification of the shell structure with thermal processes to enhance their mechanical behavior. These versatile nanoparticle-shelled bubbles are optimal candidates to form hierarchically assembled lightweight composites with targeted mechanical properties. In composites, the precise control over the structure and properties of the fillers allows the determination of the structure-property relationship, and enables a better understanding of the effect of the nanostructure on the macroscopic mechanical response.