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Mohammad Naraghi

The focus of this research is to develop carbon nanofibers (CNFs) with controlled architecture and microstructure as the building blocks for multifunctional nanocomposites. The research includes several types of CNFs, including CNFs with porous architectures suitable for energy storage, and hollow CNFs with wall thicknesses comparable to interatomic distances that can be used as reinforcements to enhance toughness in composites. The CNFs in this study are fabricated via carbonization of multi-component polymeric precursors with and without sacrificial components. We also address the couplings between different functionalities; for instance, CNFs may carry load while simultaneously serving as electrodes for energy storage devices (supercapacitors and lithium ion batteries), Fig. 7.

Research Plan:
The REU students will work as part of a team to manufacture CNFs, control their microstructures, and manipulate their architecture and geometry. Moreover, the students will be trained on, and perform, electromechanical characterization of individual CNFs via microdevices. Students will also work with existing modeling platforms, developed in Dr. Naraghi’s lab, to better understand the mechanics of CNFs and couplings between different physical domains. More specifically, the REU students will focus on investigation of the couplings between charge storage and load bearing ability in multifunctional CNFs, serving as the building blocks of structurally integrated energy storage systems. The CNFs will be porous, where the pores are intended to provide an interface between the electrolyte and the electrode (CNFs). The student will use validated models to study the effect of pore geometry on load bearing capacity, considering phenomena such as stress concentration around discontinuities (such as pores) and crack deflection caused by the pores. This effort will be guided by pore geometries that are experimentally available, to be achieved via novel sample processing methods. The multiscale models will then be used to study tradeoffs between surface area and load bearing, arising from stress concentration around pores. Lastly, the students will study electro-chemo-mechanical fatigue in porous CNFs. Of particular interests will be to find out how the presence of pores, intended to accelerate ion transfer in lithium ion batteries and enhance energy density in supercapacitors, affect strength due to factors such as stress concentration, how ion intercalation can induce flaws, and how the presence of pores which allow stress-free swelling may mitigate this effect.