Browsing by Subject "Polymers"

Utilizing the power of Monte Carlo simulations, a novel, semi-empirical method for investigating the performance of organic photovoltaics (OPVs) in resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) films is explored. Emulsion-based RIR-MAPLE offers a unique and powerful alternative to solution processing in depositing organic materials for use in solar cells: in particular, its usefulness in controlling the nanoscale morphology of organic thin films and the potential for creating novel hetero-structures make it a suitable experimental backdrop for investigating trends through simulation and gaining a better understanding of how different thin film characteristics impact OPV device performance.

The work presented in this dissertation explores the creation of a simulation tool that relies heavily on measureable properties of RIR-MAPLE films that impact efficiency and can be used to inform film deposition and dictate the paths for future improvements in OPV devices. The original nanoscale implementation of the Monte Carlo method for investigating OPV performance is transformed to enable direct comparison between simulation and experimental external quantum efficiency results. Next, a unique microscale formulation of the Dynamic Monte Carlo (DMC) model is developed based on the observable, fundamental differences between the morphologies of RIR-MAPLE and solution-processed bulk heterojunction (BHJ) films. This microscale model enables us to examine the sensitivity of device performance to various structural and electronic properties of the devices. Specifically, using confocal microscopy, we obtain an average microscale feature size for the RIR-MAPLE P3HT:PC61BM (1:1) BHJ system that represents a strategic starting point for utilizing the DMC as an empirical tool.

Building on this, the RIR-MAPLE P3HT:PC61BM OPV system is studied using input simulation parameters obtained from films with different material ratios and overall device structures based on characterization techniques such as grazing incidence-wide angle X-ray scattering (GI-WAXS) and X-ray photoelectron spectroscopy (XPS). The results from the microscale DMC simulation compare favorably to experimental data and allow us to articulate a well-informed critique on the strengths and limitations of the model as a predictive tool. The DMC is then used to analyze a different RIR-MAPLE BHJ system: PCPDTBT:PC71BM, where the deposition technique itself is investigated for differences in the primary solvents used during film deposition.

Finally, a multi-scale DMC model is introduced where morphology measurements taken at two different size scales, as well as structural and electrical characterization, provide a template that mimics the operation of OPVs. This final, semi-empirical tool presents a unique simulation opportunity for exploring the different properties of RIR-MAPLE deposited OPVs, their effects on OPV performance and potential design routes for improving device efficiencies.

Chiral, molecular and nanoscale assemblies are promising candidates for the development of spintronic-based devices, characterized by information processing using both electronic charge and spin, and are poised to give rise to superior computational efficiency relative to modern electronic architectures that only operate using processing of electronic charge. Essential to realizing such spintronic assemblies is the ability to isolate and engineer enantiopure, chiral nanoscale materials that feature highly-tunable and unique electronic structures. Congruent with such requirements, this work focuses on engineering molecular and nanoscale organic matter that interface with single-walled carbon nanotubes (SWNTs), and are capable of: (i) generating concentrated, enantioenriched SWNT-based chiral inks from racemic mixtures that aim to be amenable with current ink-jet printing designs for electronic device fabrication, or (ii) inducing SWNT lattice handedness in achiral SWNT platforms that depend on conjugated polymer electronic structure and polymer pitch length. Specifically, this work explores: (i) experimental and computational investigation of engineered chiral, binaphthalene-based surfactant frameworks that are able to disperse and resolve enantiomers of SWNTs via enthalpic and entropic differences in surfactant-SWNT interactions in aqueous solutions, and (ii) chiral, semiconducting aryleneethynylene-based polymers that helically wrap metallic single-walled carbon nanotubes (m-SWNTs) and give rise to m-SWNT band gap opening and a metallic to semiconducting phase transition in such assemblies. Exploitation of such unique designs will enable opportunities to develop exceptional chiro-optic and spintronic materials, and help elucidate critical structure-function relationships that broadly inform material design for such applications.

In many instances of soft tissue applications, implants based on compliant polymers have proven to exhibit superior performance over those based on stiffer polymers. Combined with the capability of 3D-printing to create complex structures, many innovative implants based on compliant polymers can be envisioned. However, current literature on 3D-printed compliant polymers is limited. The motivation behind this work is to contribute to the development of 3D-printed biomedical implants that are based on compliant, elastomeric polymer for soft tissue applications. The two aims that comprise this work look to shed light on two particularly sparse areas of study, the fatigue of elastomeric 3D-printed architected structures and the structure-property relationship of 3D-printed bioresorbable elastomeric polymer. The two aims are: 1) to investigate the behavior and durability of 3D-printed polycarbonate urethane (PCU) porous membrane under cyclic loading, and 2) to study the structure-property relationships of 3D-printed poly(L-lactide-co-ε-caprolactone).

In the first aim, the mechanical properties of bulk PCU of various grades were first characterized, followed by a comprehensive dimensional and mechanical characterization of 3D-printed PCU membranes of two different pore shapes, square and bowtie. In addition to the PCU membranes, a PCU-PETG laminate membrane were also studied. The strong dependence of bulk 3D-printed PCU’s mechanical properties on its testing environment were first shown via monotonic tensile testing. Tests of samples printed with various raster angles showed differences in the defect tolerance of each PCU grade. Cyclic loading of printed PCU membrane shows a strong dependence of fatigue performance on membrane shape and loading orientation. In certain configurations, PCU membrane exhibited comparable performance to commercial polypropylene mesh. However, the PCU membranes also showed an undesirable ratcheting under cyclic loading. A PCU-PETG laminate membrane was then shown as one approach to minimize ratcheting. In the second aim, the impact of 3D-printing and annealing processes toward PLCL morphology is first evaluated. Then, the hydrolytic degradation profile of both annealed and unannealed 3D-printed PLCL scaffolds is studied. The results show that printed samples were initially fully amorphous. Subsequent aging and annealing process induced significant change in morphology via crystallization and in turn affected its physical properties. However, degradation behavior was largely unaffected by the annealing induced crystallization.

In summary, we first demonstrated the potential of PCU membranes for use in prolapse mesh application by evaluating their mechanical properties, particularly their fatigue behavior. Then, we demonstrated the structure-property relationship of 3D-printed PLCL scaffolds, with a focus on the impact of the fabrication process on degradation behavior. The results shown here should contribute well to further development of elastomeric 3D-printed implant devices.

In order to ameliorate current maladies, improvements to medicaments and treatment regimens are required. Our lab seeks to translate findings from the laboratory bench to the patient bedside using two approaches: 1) the development of RNA aptamers that bind with high affinity and specificity to defined molecular targets, and 2) repurposing cationic binding polymers as anti-inflammatory agents. This dissertation herein, discusses both of these approaches and summarizes the findings obtained during my graduate training. In the first study, I illustrate how anti-PEG antibodies are capable of binding to and inhibiting a therapeutic RNA aptamer as demonstrated by reduction in drug potency in vitro and in vivo. In the second portion, the development of novel cationic polymer derivatives is discussed, which will help us to determine nucleic acid binding polymer mediated anti-inflammatory mechanisms of action. These findings shed light on the importance of careful and considered drug design to inform the development of future therapeutics. Despite the advances in translational research, there remains a paucity in our understanding of how drugs impact the immune system and this dissertation, in toto, seeks to aid in the development of improved bona fide therapies.