Using Crystallization to Control Filler Dispersion and Vice Versa in Polymer Nanocomposites

Polymer nanocomposites consist of fillers that are less than 100 nm in (at least) one dimension mixed with a polymer matrix. The research area is exciting because these materials can exhibit combinations of properties not achievable with other constructs. The dispersion (organization) of the nanofillers in the polymer are critical to controlling nanocomposite properties. In addition, when the polymer is semicrystalline, its properties are controlled, to a large extent, by the degree of crystallinity and the morphology of the crystalline regions. This project will focus on two studies to better understand how to: 1) Use rate of polymer crystallization to organize nanofillers during solidification, and 2) Use the organization of the fillers in the melt to alter the matrix crystalline morphology. With the understanding on how these assemblies can then be manipulated under controlled processing conditions the focus will be on the optimized thermomechanical and dielectric properties relevant for applications such as insulation for high voltage electrical transmission and energy storage materials.

This project will systematically alter the compatibility of the nanofiller with the matrix using short surface ligands, and the diffusivity using polymer brushes on the nanofillers, and explore the fundamental mechanisms that will allow control over nanofiller organization as a function of the ratio of crystallization rate to diffusivity in an important class of engineering polymers, e.g., polyethylene, isotactic polypropylene. These same fillers will also be organized in the melt, and the plan is to monitor the crystalline morphology that develops, expecting that the crystals will nucleate from the nanofiller surfaces, thus providing a means for controlling the crystalline morphology as well as nanofiller dispersion. Mechanical and dielectric properties of these hierarchically organized polymer nanocomposites will be measured to identify the optimal dispersion and crystalline conditions to achieve the best performance. The experimental work will be accompanied by coarse grained computer simulations to understand the fundamental physical phenomena controlling the behavior, which can then be used in a materials design process.