Browsing by Author "Marciel, Amanda B"

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    Decoding Charge Block Sequence Effects on Polyampholyte Behavior with Synthetic Protein Analogs
    (2025-01-09) Shi, Winnie H; Marciel, Amanda B
    Polyampholytes are polymers containing both positively and negatively charged groups along their backbone. The presence of these charged residues enables the development of stimuli-responsive and multi-functional materials. Incorporating ionic groups into polymeric materials has been shown to improve thermal and mechanical properties, as well as provide anti-fouling and cryopreservation effects. Naturally occurring polyampholytes are found in intrinsically disordered proteins (IDPs), which constitute 25-30% of known functional eukaryotic proteins. IDPs play critical roles in disease due to their involvement in forming condensed phases in intracellular environments. Recent studies by computational and experimental scientists indicate that charge sequence significantly influences the phase separation behavior of IDPs. To utilize charge sequence as a design parameter for polyampholyte materials and to enhance our understanding of the electrostatic contributions to peptide phase behavior, it is essential to understand how charge sequence affects polyampholyte conformation. This thesis experimentally investigates the effects of charge sequence on polyampholyte conformation and phase behavior. Using Fmoc-based solid-phase peptide synthesis, we construct sequence-specific polyampholyte peptides with varying charge blockiness, from alternating to diblock arrangements. Experiments are conducted in dilute concentrations to better assess single-chain structure and dynamics. In the first part of this thesis, we characterize the conformation of L-chiral polyampholyte peptides. In the second part, we synthesize atactic polypeptides by incorporating D-chiral residues to better isolate electrostatic interactions and reduce hydrogen bond interactions. We generally observe increased phase separation with increased blockiness. Small angle scattering reveals that these polyampholytes exhibit random coil or self-avoiding walk conformations with minimal differences in size at small block lengths. We also observe microphase separations in mid-sized blocks of the atactic system, consistent with theoretical predictions. Lastly, we characterize the dynamics of polyampholyte solutions. All experiments are compared to solutions with added NaCl, where electrostatic interactions are screened. Comparing our experimental results with recent simulations and complexation experiments provides further insights into the thermodynamic driving forces behind our observations.
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    High-Purity 2D Perovskite Thin Films: Role of Solvent Interactions for Solution-Processed Optoelectronic Materials
    (2024-04-18) Khalili Samani, Mohammad Hossein; Marciel, Amanda B
    Perovskite solar cells have emerged as a hot topic in recent years with their promise of a cheaper and more efficient alternative to conventional silicon solar cells. While 3D perovskites have demonstrated impressive performance in solar cells, their long-term stability remains to be a challenge. This has led to exploration of 2D perovskites, which offer improved stability due to their unique atomic structure. In this thesis, we address several factors impacting stability, phase purity, and device performance of 2D perovskite systems. Firstly, we present a new synthetic route to produce single n–valued parent crys- tals. The phase selective method involves precrystallization of parent crystals with a single phase structure, that upon dissolution, yield memory seeds for a patterned growth and nucleation of thin films. Our analyses showed the parent crystals are 100% phase pure and resulting thin films have upwards of 90% phase purity with minor undesired n–phases. We monitored the seeds and growth process by dynamic light scattering and optical microscopy techniques, and fabricated devices with high stability and efficiencies (> 17%). Next, we probe the mechanism by which memory seeds interact with processing solvents of varying propertie, including polar, hydrogen bonding, van der Waals inter- actions to deepen our understanding of the dissolution process of phase-pure parent crystals. We leveraged dynamic light scattering, microscopy, and spectroscopy tech- niques to monitor different steps of film formation. Our study demonstrates that solvents exhibiting high propensity for hydrogen bonding and diminished dispersion forces promote the formation of thin films with superior phase purity and the tar- geted out-of-plane orientation. Conversely, solvents with dominant dispersion forces and a diminished capacity for hydrogen bonding lead to the formation of thin films exhibiting poor phase purity, diminished excitonic peak intensities, and an undesired in-plane orientation. Lastly, we increased device efficiency by employing lithium-doped nickel oxide (Li-doped NiOX) as the hole transport layer (HTL). This Li-doped HTL not only improves the physical characteristics of the 2D perovskite film structure, crystal formation, and alignment, but also optimizes the energy levels within the device, leading to efficient charge extraction. Furthermore, the resulting 2D perovskite solar cells with Li-doped NiOX demonstrate excellent stability under light exposure. In summary, this thesis presents works on improving stability, efficiency, and life-time of solar cell devices based on 2D metal halide perovskites. This goal has been achieved by engineering of different steps leading to the device fabrication, such as optimization of crystal synthesis, solvent-perovskite interactions, and transport layer engineering of the device module.
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    Structure and Dilatational Response of Asphaltenes with Varying Solvent Quality
    (2024-12-06) Pagan Pagan, Nataira M; Marciel, Amanda B
    Defined by their solubility class, asphaltenes represent the most polar, aromatic, and heaviest fraction of crude oil. They strongly adsorb at oil-water interfaces, forming viscoelastic films that confer solid-like mechanical properties that stabilize crude oil emulsions. It is suggested that asphaltenes form the most stable crude oil emulsions close to the onset point of precipitation, in which soluble and insoluble asphaltene nanoaggregates are in solution. The formation of these emulsions leads to undesired flow assurance problems for the oil and gas industry that require demulsification to prevent operational challenges and costs. Given the heterogeneity in chemical composition, structure, and molecular weight of natural asphaltenes, it remains challenging to identify how their aggregation, precipitation, and diffusion behavior at oil-water interfaces promote stability. We use small-angle X-ray scattering (SAXS) and the oscillating pendant drop method to address this challenge and investigate the structure, aggregation behavior, and the dilatational rheology of asphaltenes and asphaltene-model molecule violanthrone-79 (VO-79) with decreasing solvent quality. We observed that the radius of gyration (Rg) is independent of solvent quality before the onset point of precipitation and decreases as solvent quality decreases. In addition, our results show that the complex dilatational modulus of soluble asphaltene nanoaggregates depends on the solvent quality and increases with aging. On the contrary, the interfacial dilatational response of VO-79 remains relatively constant with increasing aging and decreasing solvent quality. We hypothesize that soluble asphaltene nanoaggregates may be re-arranging at the oil-water interface due to their dispersed nature, thus influencing their packing and enhancing the mechanical proper- ties of the asphaltene-stabilized interfacial film, thereby promoting emulsion stability. The direct connection between structure and the dilatational response of oil-water interfaces stabilized by soluble asphaltenes is essential for understanding their interfacial properties and their role in the emulsification process near the onset point of precipitation. Understanding the relationship between the structural and interfacial features of soluble asphaltenes provides insights into developing effective demulsification strategies to prevent flow assurance issues associated with asphaltene-stabilized crude oil emulsions. Additionally, this work demonstrates feasibility in emulsion-based industrial applications.
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    Synthesis and physical behavior of weak polyelectrolyte brushes
    (2024-04-16) Ramezani Bajgiran, Shahryar; Marciel, Amanda B; Verduzco, Rafael
    Weak polyelectrolyte brushes (PEBs) consist of weakly charged polymers grafted to a surface and have emerged as promising candidates for responsive coatings due to their remarkable ability to undergo significant swelling and deswelling in response to changes in pH and ionic strength. This unique property holds immense potential for diverse applications in separation processes, drug delivery, and biosensing. The full potential of weak PEBs, however, is hampered by an incomplete understanding of their swelling behavior in response to various stimuli. Moreover, it has been shown that the swelling behavior of weak PEBs has a hysteretic memory response. This phenomenon manifests as a distinct difference in the swelling response when increasing or decreasing the pH, leading to unpredictable and unreliable performance in practical applications. To address these challenges, a comprehensive understanding of the physical factors that govern the swelling behavior of weak PEBs is essential. In this work, we investigated how pH, salt, and ionizable monomer fraction influence weak PEB swelling behavior. We synthesized a series of weakly charged polybasic brushes with varying fraction of ionizable monomers using an environmentally friendly surface-initiated polymerization technique with superior control and reproducibility over the polymerization kinetics. We used spectroscopic ellipsometry (SE), atomic force microscopy (AFM), and surface zeta potential measurements to characterize the swelling behavior and charge state of the brushes. We found that the pH-dependent swelling and hysteretic behavior of weak PEBs significantly increase as the fraction of ionizable monomers increases. Whereas salt concentration results in a complex non-monotonic swelling and hysteretic behavior. Lastly, to better understand the transport of particles within weak PEBs, we used a 3D super resolution tracking technique on a model charged tracer. We uncover significant spatial heterogeneities and find two distinctly different modes of motion within a weak PEB. Overall, our findings on the swelling behavior of weak PEBs and their interactions with particles can facilitate the design of more efficient stimuli-responsive coatings that use weak PEBs in various applications.