Seminar Speakers: NC State MSE Grad Students Ul-Mahmood, Daigle and Taussig

Excellence in Graduate Research

“Computational Studies of High Entropy Ceramics”

High entropy ceramics are a novel class of chemically disordered crystalline materials with promising properties for application in catalysis, barriers for thermal and environmental protection, substrates for water splitting, and energy storage materials. While the presence of many atomic species is important for thermochemical stability as well as structural and functional properties, it creates special challenges to predicting phase stability and defect properties. My graduate work combines atomistic simulation using density functional theory and statistical modeling with an emphasis on uncertainty analysis to explore the vast combinatorial and configurational space of high entropy transition metal carbides, seeking to understand order-disorder phenomena and their relation to defects and interfaces.

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“Electrostatic Self-Assembly Induces Water-Stabilized PEDOT:PSS for High-Performance OECTs”

Organic bioelectronics and in particular organic electrochemical transistors (OECTs) are gaining importance for their investigation and replication of complex biological processes of the human brain. However, the most successful material used to make OECT channels is a water-processed and water-soluble conducting polymer that dissolves in aqueous environments without chemical crosslinking. This creates a fundamental stability-performance compromise whereby stability is achieved at the expense of order, carrier mobility, free volume, and volumetric capacitance. Here, we demonstrate a conceptual breakthrough in electrostatic self-assembly (ESA) of colloidal PEDOT:PSS that enables facile processing of a water-stable form of PEDOT:PSS. Using advanced characterization and computations, we demonstrate how ESA leads to the formation of long-range fibular morphology composed of co-crystal structures to stabilize the material and enable simultaneous charge transport and ion permeation during OECT operation.

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“New Molecular Models and Methods for Simulations of Magnetic Nanoparticles”

Magnetic nanoparticles (MNPs) can organize into novel structures in solutions with excellent order and unique geometries. However, studies of the self-assembly of smaller MNPs are challenging due to a complicated interplay between external magnetic fields and van der Waals, electrostatic, dipolar, steric, and hydrodynamic interactions. Here, we present a novel all-atom molecular dynamics (AMD) simulation method to enable detailed studies of the dynamics, self-assembly, structure and properties of MNPs as a function of core sizes and shapes, ligand chemistry, solvent properties and external field. We demonstrate the use and effectiveness of the model by simulating the self-assembly of oleic acid ligand-functionalized magnetite (Fe₃O₄) nanoparticles, with spherical and cubic shapes, into rings, lines, chains, and clusters under a uniform external magnetic field. We found that the long-range electrostatic interactions can favor the formation of a chain over a ring, the ligands promote MNP cluster growth, and the solvent can reduce the rotational diffusion of the MNPs. The algorithm has been parallelized to take advantage of multiple processors of a modern computer and can be used as a plugin for the popular simulation software LAMMPS to study the behavior of small magnetic nanoparticles and gain insights into the physics and chemistry of different magnetic assembly processes with atomistic details.