Session Q04: Condensed Matter Physics

Kinetic Simulations of Intense Laser-Dielectric Interactions

We present a novel three-dimensional framework for simulating intense short-pulse lasers interacting with dielectric materials. Our work modifies the open-source Particle-In-Cell (PIC) code EPOCH to include new models for molecular photoionization, dielectric optical response, and impact ionization. We use this framework to model the laser-induced damage of dielectric materials by few-cycle laser pulses. A sequence of simulations with varying laser fluence allow us to better understand the laser damage process by providing new insight into energy absorption, excited particle dynamics, and nonthermal excited particle distributions.  Additional applications of this framework include laser damage of multilayer interference coatings to improve next-generation optics and modeling of the extreme conditions created from laser-microstructure interactions.   

Characterization of Graphene Oxide Composites in a Matrix of High and Low Molecular Weight Polyvinyl Alcohol

Graphene oxide (GO) has been combined with polyvinyl alcohol (PVA) to make composite films with improved properties such as high tensile strength, increased optical conductivity and high refractive index. Different methods of processing GO/PVA composites have led to reduction in GO resulting in improvements of electrical conductivity of the films. Films prepared on glass substrates using high molecular weight PVA demonstrated an electrical conductivity that increased with the GO concentration. However, these films appeared porous and had poor adhesion to the substrate. When low molecular weight PVA was used as the matrix material, the GO composites showed improved film properties resulting in uniform and coherent films. However, these films demonstrated an electrical conductivity that was lower compared to the ones prepared with high molecular weight PVA. Therefore, various combinations of low and high molecular weight PVA at different ratios were investigated to optimize electrical conductivity and film properties. Mixtures of high- and low-molecular weight PVA/GO films resulted in higher electrical conductivity after subjecting to thermal processing. Resistance readings were taken in fixed width strips to calculate the resistivity and conductivity. ATR-FTIR data revealed the transformation of functional groups in optimized films. These optimized GO/PVA films may find usage in energy storage systems, solar cells, and other electronic applications.   

Heterogenous mixed-molecular weight polymer brushes as neutral templates for block-copolymer orietation control.

Distinctive polymer brushes play a crucial role in providing a neutral surface conducive for orientational control of block copolymers (BCPs). This bottom-up approach effectively align the formation of lamellar-like, cylinder, sphere, or gyroid structures of BCP thin films for use as nanopaterning templates. These templates modified for pattern transfer in applications such lithography, photovoltaics and membranes structures. In conventional BCP self-assembly techniques, random copolymers (RCPs) brushes are commonly employed to achieve substrate neutrality. However, these methods face significant drawbacks, including batch variations and lack of ability to tune surface energy during grafting. To address these issues, various approaches have been proposed to mitigate inconsistencies and enhance tunability, albeit with associated costs. Our proposition involves a system of polymer brushes composed of Polystyrene (PS) and Poly(methyl methacrylate) (PMMA) with mixed ratios, polymer chain lengths, and chemical enhancement. This system aims to effectively control surface energy combining the effects of chemistry and macromolecular structure, which offers a straightforward, low-cost template to serve as a tunable neutral brush for BCP self-assembly.   

Pore Fouling in Azo-Dye-Functionalization Membranes

The textile dye industry is one of the largest polluters of freshwater on Earth, contributing to the nearly 2.8 x 10⁵ tons of synthetic textile dyes discharged into the environment annually. While this specific type of pollution occurs in specific areas around the World, the effects are of global concern. Recent research shows that polycarbonate filters functionalized with anionic azo dyes have the potential to enhance dye rejection, leaving nearly completely decolorized water after filtration in specific instances. This process, referred to as azo-dye-functionalization, provides an elegant solution to water pollution by textile dyes, demonstrating that the textile dyes, hence the contaminants themselves, are part of the solution. By using data for an anionic direct dye series at 1000µM and models that already exist in literature, this work aims to understand and highlight the pore fouling that occurs at the polycarbonate surface during the functionalization process. By keeping the charge of the dyes fixed, the dependency of charge is eliminated, allowing for the examination of structure and functional end groups effect on pore fouling. To test for functionalization, direct red 28 and direct red 81 were cycled from low concentration to high concentration and back. Both showed hysteresis (changes) in the data as the concentration was increased and then decreased, with direct red 28 having larger hysteresis than direct red 81. In the end, this research paves the way for the overall goal of water purification of textile dyes and other charged contaminants.   

Investigating the Strain Effect on Thermoelectric Properties

Thermoelectric materials directly convert waste heat to electricity and offer significant potential to contribute to a global sustainable energy solution; however, they have yet to reach the maximized conversion efficiency. In recent decades, various methodologies, including alloying, quantum size effects, nanostructuring, and strain, have been explored to tune material parameters and enhance conversion efficiency. Among these strategies, lattice strain engineering has emerged as a promising approach to enhance thermoelectric efficiency. Motivated by this, we investigate the effect of strain on the electronic structures and thermoelectric transport properties using advanced first-principles calculations.