NH BioMade Publications

Acta Materialia, 261, 119395. doi:10.1016/j.actamat.2023.119395

Scientific Reports doi: 10.1038/s41598-023-41947-z

Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Mechanical Engineering.

DISSERTATION ABSTRACT:
Stress superposition is defined as the incorporation of additional stresses into an existing manufacturing process during a single operation. In this thesis, experiments, simulations, and modeling of stress superposition in sheet metal deformation were investigated. Stress superposition can be used in manufacturing to reduce forming forces, increase material formability, and tailor the final part properties of products according to their intended applications, creating so-called functionally graded materials. Austenitic stainless steels (SS) were the focus due to their susceptibility to strain-induced phase transformation from austenite to martensite based on the stress state applied. In the first chapter, a novel cruciform specimen was designed to improve material characterization and modeling, which were essential to accurately determine how to adjust the parameters of the manufacturing processes to affect the final part properties. Next, parameters were identified for a martensitic transformation kinetics model experimentally and implemented into a single point incremental forming finite element model. The simulations were validated by experimental results for a truncated square pyramid. After that, To demonstrate the stress superposition strategy with corresponding finite element analyses, the superposition of tensile and compressive stresses into single point incremental forming was used to vary the phase transformation in the formed parts. Then, the continuous bending under tension process was used to investigate the residual stress development and phase transformation under the complex stress states inherent to the process. In future research, these results will inform further studies focused on exploiting stress superposition to improve metal forming processes, e.g., manufacturing heterogeneous trauma fixation hardware components, i.e., implants to hold fractured bones together during healing, using double-sided incremental forming as a proof-of-concept for the application of this work in industry. 

Journal of Chemical Theory and Computation doi: 10.1021/acs.jctc.3c00406

Proceedings of the 14th International Conference on the Technology of Plasticity - Current Trends in the Technology of Plasticity, 475–485. doi: 10.1007/978-3-031-40920-2_49.

Protein Science doi: 10.1002/pro.4720

Journal of Materials Research and Technology  doi: 10.1016/j.jmrt.2023.06.059

Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy In Chemical Engineering.

DISSERTATION ABSTRACT:
Sepsis is a complicated medical emergency and critically ill patients suffering from infectious diseases are at a high risk for developing and dying from sepsis. According to a recent (2019) cohort study from six United States hospitals, suboptimal care (e.g., delay in antibiotics, inappropriate antibiotic therapy) is responsible for 22.7 % of in-hospital sepsis-associated deaths. In September 2020, the World Health Organization called on the scientific community to develop rapid, effective, and affordable tools to improve diagnosis, surveillance, and treatment of sepsis. Our long-term goal throughout this project is to develop a cyclodextrin (CD) impedimetric tongue that can provide early warning of sepsis by continuous monitoring the course of the disease and real-time profiling of urine samples in hospitalized patients. The cyclodextrin impedimetric tongue will also enable healthcare professionals to closely monitor the patients, predict sensitivity and resistance to therapies, decide about the dose of medications, and develop more effective personalized therapies for septic patients. Cyclodextrins, oligosaccharides with a hydrophobic cavity and a hydrophilic surface, are promising biorecognition elements in development of reusable impedimetric tongues. Cyclodextrins can semi-selectively detect different metabolites in the solutions through hydrophobic interactions, Van der Waals forces, and hydrogen bonding. The first aim of this thesis was to develop the first reusable nanostructured cyclodextrin platform using αCD and a weak surface αCD mediator: polyethylene glycol (PEG). To create the Gold-PEG:αCD surface, gold surface was modified with PEG via thiol-gold chemistry and the PEG support enabled reversible immobilization of αCD. We investigated the performance of this platform for detection of a XVI model hydrophobic analyte, trans-resveratrol. Non-faradaic electrochemical impedance spectroscopy (EIS) measurement of the surface suggested that when αCD surfaces are introduced to a solution containing trans-resveratrol, αCD molecules leave the PEG support to interact with trans-resveratrol in the solution. After use, the surface could be regenerated by reloading of αCD. The second aim of this thesis was to improve the stability and reusability of cyclodextrin sensing platform by replacing gold-thiol bonds with carbon-carbon covalent bonds between glassy carbon (GC) and 4-carboxyphenyl diazonium salt. The GC-carboxyphenyl was modified with polypropylene glycol (PPG) through EDC/NHS chemistry. The PPG surface was then loaded with βCD. We used the GC-carboxyphenyl-PPG:βCD surface for sensitive detection of cortisol in biofluids (i.e., urine and saliva), and demonstrated the successful regeneration and reuse of the GC-carboxyphenyl-PPG:βCD surface for ten times. Finally, we employed sensitive, stable, and reusable cyclodextrin nanostructured surfaces to develop the first-generation cyclodextrin impedimetric tongue for separation and classification of four classes of bioanalytes including creatinine, cortisol, glucose, and fumarate. We applied linear discriminant analysis (LDA) to integrate and map the data, and by using the normalized changes in imaginary capacitance of three cyclodextrin surfaces (γCD at 79 Hz, hydroxypropyl-βCD at 0.25 Hz, and hydroxypropyl-γCD at 63.34 Hz), we achieved the 5-fold cross validation accuracy of 69%. Different methods of data preparation, EIS signal processing, and determining the characteristic frequencies of different analytes and single frequencies of cyclodextrin surfaces affect the accuracy of the impedimetric tongue. By optimizing these parameters, we can improve the performance and accuracy of the impedimetric tongue and apply this device for point of need applications.

CIRP Annals doi: 10.1016/j.cirp.2023.04.015

Macromolecules doi: 10.1021/acs.macromol.2c02378

Chemical Society Reviews doi: 10.1039/D2CS01011A

Korean Journal of Chemical Engineering doi: 10.1007/s11814-022-1293-y

Materials  doi: 10.3390/ma16020572

Journal of the American Chemical Society doi: 10.1021/jacs.2c05510

Computer Methods in Applied Mechanics and Engineering. doi: 10.1016/j.cma.2022.115740

Biofabrication doi: 10.1088/1758-5090/ac94a1

ASME 2022 17th International Manufacturing Science and Engineering Conference doi: 10.1115/MSEC2022-85595

Proceedings of the ASEE 2022 Annual Conference. https://peer.asee.org/41107 

Journal of Medical Devices. doi: 10.1115/1.4055249

ACS Applied Materials & Interfaces, 14(37), 42374–42387. doi: 10.1021/acsami.2c07701

Journal of Chemical Information and Modeling, 62(14), 3381–3390. doi: 10.1021/acs.jcim.2c00376

International Journal of Plasticity, 156, 103367. doi: 10.1016/j.ijplas.2022.103367

STAR Protocols. doi: 10.1016/j.xpro.2022.101523

IOP Conference Series: Materials Science and Engineering doi: 10.1088/1757-899x/1238/1/012085

Proceedings for IISE Annual Conference & Expo 2022

Polymer Chemistry doi: 10.1039/D1PY01472B

International Journal of Mechanical Sciences doi: 10.1016/j.ijmecsci.2022.107663

DISSERTATION ABSTRACT:
Total joint devices that can survive more than 20 years in vivo require a bearing surface that can combine toughness, wear resistance, and chemical stability. Ultrahigh molecular weight polyethylene (UHMWPE) remains the gold standard for these bearings, having been utilized as a liner and bearing surface for over five decades. Well-documented material trade-offs lead to failure modes that suggest that hip liners and knee bearing surfaces without optimal processing may be prone to premature failure in the patient. Because the demographic of those receiving implants is changing and smart materials and devices are seeing increased use in medicine, implants may need to be more functional to allow optimization for the patient of the future. The present work explores material trade-offs by attempting to alter the microstructure of UHMWPE through the use of a severe plastic deformation technique known as equal channel angular pressing (ECAP). Work was performed to confirm the validity and reliability of dynamic mechanical analysis (DMA) as a rapid means to indicate and assess changes to the microstructure of UHMWPE in the form of entanglement density and chain interactions. ECAP was applied to both neat and conductive composites of UHMWPE in order to understand the microstructural and mechanical changes due to shearing. Two grades of UHMWPE were used to understand the impact of MW, a variety of temperatures were employed to better optimize shear strain, and consolidation and extrusion hydrostatic pressures were altered to determine if chain mobility and consolidation were hindered under large compressive forces. Preliminary modeling of the different thermal gradients that ECAP and compression molded (CM) controls are exposed to was carried out to aid in and inform future experiments. While ECAP did not reveal changes to the microstructure of neat materials as compared to compression molded (CM) controls, work-to-failure was decreased which is hypothesized to be due to residual stresses. Carbon composites, on the other hand, were shown to have increased work-to-failure after shearing which was coincident with a decline in conductivity as compared to CM controls.

Submitted to the University of New Hampshire In Partial fulfillment of The Requirements for the Degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Certain organisms living in cold regions have adapted different strategies to survive in harshly cold temperatures. Some of them use freeze-avoiding strategies in which they can prevent freezing by controlling the concentration of sugars (et. sucrose, trehalose) or polyols (glycerol), regulation of the ice nucleator, and dehydration. Other organisms have adapted to this extremely cold condition by producing antifreeze (gly)proteins (AF(G)Ps) which exhibit ice recrystallization inhibition (IRI), thermal hysteresis activity (THA), and dynamic ice crystal shaping. These proteins discovered in Antarctic fish in 1960 for the first time have been reported in bacteria, fungi, insects, and plants. AF(G)Ps and their synthetic biomimetics have received increasing attention as potential candidates for various industrial and bio-medical applications. Promising results from vitrification and other protocols using antifreeze agents with ice recrystallization inhibition activity have widely been reported in biopreservation. Conversely, understanding of the antifreezing process caused by these macromolecules remains under challenge. This is due to the multifunctional nature of the freezing process and antifreeze macromolecule’s behavior which brings complexity in designing the synthetic antifreeze structures. In addition, the cost, low availability, toxicity at higher concentrations, and instability beside several other drawbacks make their large-scale production challenging. Although several synthetic attempts for the exploitation of AFPs have been studied in the past, challenges remain in the synthetic design of AFP analogs. On the other hand, poly (vinyl alcohol) (PVA) with simple structure has been reported with potent IRI activity as a good candidate for large-scale production and applications.

Our group has explored structural variations to polyol-based polymers to contrast with PVA as a control and identified several key structural elements for performance in IRI, THA, as well as in ice nucleation inhibition (INI). These structural features are bioinspired by the typical ice-binding plane of AFPs yet are surprisingly simple to produce with potency approaching that of typical AFPs. Key to the performance is positioning small organic functionalities with known antifreeze properties (glycerol) pendent to a host polymer chain with consideration of their conformational freedom. To build systematic variations into both the backbone and side-chain structures, we used poly (vinyl alcohol), poly (isopropenyl acetate), poly (acrylic acid), and poly(methacrylic acid) xvi parent polymers for such pendent modifications. One structure in particular, glycerol-grafted-PVA (G-g-PVA), shows potency rivaling that of AFPs at similar micromolar concentration. The findings in this study help guide the rational design of synthetic antifreeze polymers useful for applications such as anti-icing coatings through to cryopreservation methods for organ transport and cell preservation.

While AFPs are well-known for their ice nucleation and recrystallization inhibition activity along with controlling the ice crystal morphology, the contrasting behavior of ice nucleation promotion by AFPs and its key contribution to the whole antifreezing process also seems necessary to explore in this context. Here, silver iodide (AgI) has been used as an ice nucleator in different polymer solutions in ultra-pure water (UPW) to imitate the ice nucleation process by AFPs. PVA prepared by RAFT polymerization and our glycerol grafted derivative (G-g-PVA), now shown to be the most IRI active polymer to date, was investigated for its ice nucleation and recrystallization activity in AgI dispersion media. The results showed that the ice nucleation rate and temperature was significantly changed by adding the AgI dispersion in PVA and G-g-PVA solutions. The polymer solution in UPW containing AgI dispersion showed significant improvement in IRI activity compared the same polymer in PBS buffer solution. Our results demonstrate the considerable contribution of the ice nucleator in ice nucleation rate and temperature which enhances IRI activity of synthetic antifreeze polymers. These finding both aid our understanding of the ice nucleation promotion impact on synthetic polymers IRI activity along with engineering biomimetics for biomedical and industrial applications.

Next, we focused our efforts to transfer these functionalities and performance to the solid-state interface with water. Aqueous dispersions of polymeric colloidal particles served as this substrate and were functionalized with either PVA or G-g-PVA grafted to their surfaces to contrast with performance of the same polymers strictly in the solution state. These functionalized colloids also can be applied as a continuous coating through latex film formation to assess anti-icing and iceadhesion properties. While these systems also showed encouraging and potent activity, their performance was not enhanced compared to that of the solution state systems. This may have implications for fully solid-state anti-icing coatings, yet our attention then shifted from this scope of work to new funding which required again a solution state approach. 

In this final application, we explored PVA and G-g-PVA synthesized in our lab for their biopreservation aspects especially for red blood cell (RBC) cryopreservation at -80 °C. Our results again confirmed G-g-PVA to be an excellent candidate for cryopreservation and quite likely for organ cryopreservation. Using this polymer in solution as a cryoprotectant for RBCs showed significant improvement to controls, preventing hemolysis (cell rupture) along with eliminating other drawbacks that have been observed when using small molecule cryoprotective agents like glycerol, dimethyl sulfoxide (DMSO), etc.; especially with regard to the ability to fully remove all traces of the cryoprotectant after cryopreservation storage and thawing.

In summary, the studies in this dissertation provide critical insights and approaches for the understanding of the freezing process and ideas that can help understand relevant mechanisms of influencing key freezing steps that have not yet been fully understood. In addition, it provides guidelines to synthesize G-g-PVA, currently the most potent active polymer in terms of IRI and THA shown useful for several high impact applications. In particular, this research provides valuable data and experimental conditions to understand the IRI mechanism to use in engineering next generation highly efficient antifreeze systems. 
 

Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Master of Science in Chemistry.
THESIS ABSTRACT: 
Understanding the properties of bioconjugates and biomaterials has increasingly become the focus of pharmaceutical companies, material scientists, and academia due to their growing list of applications. Bioconjugates have found broad use in therapeutics, drug delivery, tissue engineering, and biosensing. Historically, interest in specific bioconjugates has depended on the cost-availability of the biomacromolecule, making proteins the most well studied, given their relatively low cost and ease of production. However, recent technological advances in plasmid DNA (pDNA) production from E. Coli allow for greater cost-efficiency, changing the landscape ofbiomaterial research. Employing alkylating agents with known chemo-selectivity to nucleophilic sites on DNA, a polymer or polymerization agent can be coupled to biologically derived pDNA. Subsequently, properties of the hybrid-DNA bioconjugate can be controlled via the location of alkylation, to tune degradation rate and stability of the DNA bioconjugate and graft-from polymerization to increase stability and solubility. 

Computational Materials Science   doi: 10.1016/j.commatsci.2022.111348

Mahmud, M.S. (2022) "Healthcare data analytics for wearable sensors". In E.M. Narvaez, C. Dincer (Ed.). Wearable Physical, Chemical and Biological Sensors: Fundamentals, Materials and Applications (pages 169-182). Elsevier. doi: 10.1016/c2019-0-04003-4

Journal of Applied Polymer Science doi: 10.1002/app.52175

International Journal of Molecular Sciences.  doi: 10.3390/ijms222413481

ACS Applied Materials & Interfaces  doi: 10.1021/acsami.1c14453

Chemical Society Reviews doi: 10.1039/d1cs00600b

DISSERTATION ABSTRACT:
Metal–Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) are emerging materials with multifunctional properties that allow them to address global issues in chemical separations and sequestration, chemical sensing, and energy storage and conversion. Many of these applications rely on the ensemble of host–guest interactions between targeted molecular species and the surface of the framework to imbue selective properties that enhance applied performance metrics. Design principles guiding the construction of materials with desired surface chemistry and functionality are lacking for framework materials targeted towards chemical sensing. A better fundamental understanding of how host–guest interactions inform function and how host sites can be designed into a framework system through bottom-up synthetic techniques is required to advance the field of framework materials for electroanalysis. In four chapters, this thesis provides insight into the role of surface chemistry in chemical sensing in both the liquid and gas phase and how the interplay between surface chemistry and conductivity can be controlled by the strategic choice of starting materials and material morphology to produce materials with robust capabilities in chemicals sensing.

Biophysical Journal. doi: 10.1016/j.bpj.2021.10.007

Frontiers in Physics. doi: 10.3389/fphy.2021.767623.

Physical Chemistry Chemical Physics. doi: 10.1039/d1cp03822b

Submitted to the faculty in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Designing 3D printable supramolecular materials that can amplify molecular level functions to macroscale promotes the construction of advanced architectures with superior properties, thus accelerating the development of stimuli-responsive materials into integrated devices. Cyclodextrin-based poly(pseudo)rotaxanes, referred to as polyrotaxanes and polypseudorotaxanes, are ideal candidates to exercise the designing principles of 3D printable mechanically interlocked molecules (MIMs) for functional materials, due to their facile synthetic methods, variable stimuli responsiveness, and excellent biocompatibility. In this thesis, I set out to design 3D-printable cyclodextrin-based poly(pseudo)rotaxanes with their molecular motions synchronized to be amplified at the macroscale, subsequently exploiting designed macroscopic shapes with complex structures to advance their macroscopic machinery behaviors.

First, I identified designing principles to facilitate the 3D printability of MIMs for direct ink writing: (1) tailoring the dynamic interactions between binding motifs, such as hydrogen bonding between cyclodextrins, to allow the shear-thinning and rapid self-healing properties; (2) controlling assembled architectures to reinforce the polymer networks. By synthetically navigating the crystalline inclusion complexes to amorphous products with higher crosslinking degrees via the design of speed bumps or side-chain architectures, crystalline precipitates were converted to viscoelastic hydrogels that are favorable for 3D printing and mechanical adaptability. These insights allow us to design a series of 3D-printable cyclodextrin-based poly(pseudo)rotaxanes with controllable network structures and superior mechanical and responsive properties.

Second, I have also demonstrated an approach to synchronize the molecular motions of the mechanically interlocked rings and amplify them to perform mechanical work by switching the motions of the rings between random shuttling and stationary states through different external stimuli. This allows us to develop a family of actuators or mechanically adaptive materials that respond to solvent, pH, temperature, humidity and cyclodextrins, in which their macroscopic motions and materials properties rely on the control of molecular motions or features and hierarchical control across nano-to-macroscale.

Another interesting class of polyrotaxane materials I discovered are anti-freezing hydrogels with excellent mechanical properties. By noncovalently connecting polyrotaxane and polyacrylamide via hydrogen bonds, the resultant pseudo-slide-ring network hydrogels possess high stretchability, high toughness, good electrical conductivity at sub-zero temperatures, paving the way for a wide range of hydrogel applications under extreme environments.

Materials Horizons. doi: 10.1039/d1mh01108a.

Materials Science and Engineering: A. doi: 10.1016/j.msea.2021.141876

Volume 1: Additive Manufacturing; Advanced Materials Manufacturing; Biomanufacturing; Life Cycle Engineering; Manufacturing Equipment and Automation. doi: 10.1115/msec2021-63471

Proceedings of the 2021 IISE Annual Virtual Conference.

Forming the Future. doi: 10.1007/978-3-030-75381-8_155

Chem. doi: 10.1016/j.chempr.2021.06.004

JOM. doi: 10.1007/s11837-021-04715-w

CIRP Journal of Manufacturing Science and Technology. doi: 10.1016/j.cirpj.2021.04.006

Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Mechanical Engineering.
DISSERTATION ABSTRACT:
3D woven carbon/epoxy composites are high-performance materials with superior thermomechanical and physical properties making them an integral part of the aerospace, energy and automotive industries. However, under certain manufacturing conditions, these composites may accumulate severe intrinsic manufacturing-induced residual stresses which can even lead to microcracking. The complex reinforcement architecture makes analytical, numerical and experimental analysis of these composites challenging. This research has been focused on micromechanical analysis, computational modeling, and experimental characterization of 3D woven carbon/epoxy composites aiming to evaluate the manufacturing-induced residual stresses and enable mitigation of their negative impact on the resulting performance. A procedure to develop high-fidelity meso-scale finite element models with as-woven representation of the composite reinforcement informed by the μCT scanning was proposed. A set of meso-scale models for different reinforcement architectures was produced and utilized to predict the accumulation of intrinsic manufacturing-induced residual stresses in these composites. The models were correlated to the blind hole drilling experiments and used for interpretation of the experimental results providing full-field spatial distribution of the residual stresses accumulated in the composite specimens. A new simplified approach to account for nonlinear effects in the material due to severe residual stresses using linearly-elastic models was proposed. A set of parametric numerical studies was performed to improve correlation of the models with the experimental measurements. The developed meso-scale models were used to predict effective coefficients of thermal expansion for the composites with temperature-dependent properties of the constituents. Methods presented in this work provide valuable tools for the field of computational and experimental mechanics of textile composite materials.
 

The Journal of Physical Chemistry B. doi: 10.1021/acs.jpcb.0c11096

Materials Science and Engineering: A. doi: 10.1016/j.msea.2021.140980

Journal of Chemical Theory and Computation. doi: 10.1021/acs.jctc.0c01199

Journal of Materials Science & Technology, doi: 10.1016/j.jmst.2020.12.047

Biophysical Journal, doi: 10.1016/j.bpj.2020.12.010

Journal of the American Chemical Society, doi: 10.1021/jacs.0c07041

ACS Macro Letters, 9, 1836-1843. doi: 10.1021/acsmacrolett.0c00774

Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Master of Science in Mechanical Engineering.
THESIS ABSTRACT:
This work presents improvements to the methods used in crystal plasticity simulations. It shows how these improvements can be used to accurately predict the deformation behavior of two magnesium alloys, WE43, and AZ31. The first improvement to the methodology is guidance on the type of finite elements to use in explicit grain crystal plasticity simulations. This study found that quadratic tetrahedral and linear hexahedral elements are the most accurate element types included in the study. The study also concluded that tetrahedral elements are more desirable due to fast mesh generation and flexibility to describe geometries of grain structures. The second improvement made was the addition of a numerical scheme to enable the use of any rate sensitivity exponent in the fundamental power-law representation of the flow rule in crystal visco-plasticity. While allowing the use of even very large exponents that many materials exhibit, this numerical scheme adds little to no increase in computational time. This crystal plasticity model was used to accurately predict the deformation behavior of both WE43 and AZ31 under quasi-static and high rate deformation, predicting the stress-stain response and the evolution of texture, twinning and the relative activities of the various deformation modes.
 

Materials Science and Engineering: A. doi: 10.1016/j.msea.2020.140478

Soft Matter, 16, 8101-8107. doi: 10.1039/d0sm00954g

 International Journal of Plasticity, 136, 102807. doi: 10.1016/j.ijplas.2020.102807

Nano Research. doi: 10.1007/s12274-020-2874-x

Chemistry of Materials. doi: 10.1021/acs.chemmater.9b05289

Submitted to the University of New Hampshire In Partial Fulfillment of the Requirements for the Degree of Master of Science In Chemistry May 2020.
THESIS ABSTRACT:
This thesis explores the use of Diels-Alder functionalized particles to aide in the mechanical enhancement of additively manufactured objects. To date, materials generated via additive manufacturing lack isotropic properties due to the nature in which they are created – in a layer by layer fashion. This methodology often leads to poor interfacial adhesion at the junction between printed layers, lowering the stability of the part and thereby limiting its use in many applications. Dynamic covalent chemistry, such as the reversible Diels-Alder reaction, has the ability to alleviate this anisotropy to print stronger, more uniform objects. To do so, this work investigates crosslinked, Diels-Alder functionalized particles generated by two separate methods: polymerization via reversible addition fragmentation chain transfer (RAFT) followed by atom transfer radical coupling (ATRC) and free radical emulsion polymerization. These particles can be blended with a polymeric filament for 3D printing, where upon heating during the extrusion process of additive manufacturing, the retro-Diels-Alder reaction is initiated and releases the crosslinked particles exposing reactive diene and dienophile pairs. In subsequent xvii cooling after the printing process, these moieties undergo the forward Diels-Alder reaction and form chemical linkages between printed layers of the substrate to improve the mechanical integrity and uniformity of objects produced by means of additive manufacturing.

Journal of the American Chemical Society. doi: 10.1021/jacs.9b13402

Soft Matter. doi:10.1039/c9sm01878f

Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Master of Science in Mechanical Engineering September, 2019.
THESIS ABSTRACT:
The following research explores the continuous bending under tension (CBT) incremental forming process effects on four dual phase (DP) steels: DP 590, DP 780, DP 980, DP 1180. A parameter study was conducted, finding the ideal parameters for increased elongation to fracture compared to tension of over five times for DP 1180 and DP 980. These parameters were found to be a normalized bend depth of 3.5 and a crosshead pull speed of 1.35mm/s. Using these parameters, following tests were conducted on all four steels by stopping the CBT process before fracture at 2, 4, 6, 8, and some even at 10 and 12 CBT cycles. Smaller tensile specimens were machine from these CBT processed strips and uniaxial tension tests were performed to study the residual ductility of CBT testing. The strength of all steels increased with increased cycle count by 200-400 MPa, however the ductility decreased by over half. Using neutron diffraction, the texture evolution of the CBT process was explored. Results showed a preferred orientation in the {011} fiber in the pulling direction. This research also proves simulating the CBT process and matching to experimental data can be a method for extrapolating post-necking hardening behavior of DP 980 and DP 1180. The experimental data and results are further explained in the following chapters.

Molecular Simulation, 45(14-15), 1273–1284. doi: 10.1080/08927022.2019.1634268

International Journal of Solids and Structures, 174-175, 28–37. doi: 10.1016/j.ijsolstr.2019.06.005

This dissertation has been examined and approved in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Atom transfer radical coupling (ATRC) is gaining recognition for its utility in building complex polymeric architectures because it features efficiency, a wide range of compatible substrates, and a lack of byproducts. These qualities are especially desirable in applications requiring intramolecular cross-linking as in the synthesis single-chain nanoparticles (SCNP). This dissertation aims to (I) provide motivation and context for developing ATRC technology for intramolecular cross-linking, (II) provide guidance into the impact of catalyst selection and substrate on reaction efficiency and morphology, and (III) demonstrate the possibility to sequence intrachain ATRC with ATRP to create advanced SCNP architectures. Chapter II describes the preparation of SCNP from parent polymers containing alkyl or benzyl bromide ester pendants using ATRC catalyzed by copper halides complexes. Tri- or tetradentate alkyl or pyridyl amines (PMDETA, TPEN, and TPMA), which tune the redox potential of the Cu(I)/Cu(II) system, were directly compared. Coupling efficiency was positively correlated with the kATRP of the respective catalyst systems. However, PMDETA complexes afforded greater control as evidenced by lower polydispersity. In the case of alkyl halide pendants, selectivity for coupling over disproportionation systematically decreased under conditions designed to increase the concentration of CuI /L. Polymers with benzyl bromide pendants, which cannot disproportionate, tended to produce high molecular weight products, even in ultradilute solutions (0.25 –1.0 mg/mL). xvii Chapter III describes the preparation of SCNP from parent polymers capable of initiating intra-chain polymerization by ATRP under conditions favoring termination by coupling. Because of the wide variety of compatible monomers that have been well-established for ATRP systems, the ATRP/C framework both simplifies reaction procedures (one pot polymerization and coupling strategies are feasible) and imparts handles with which to control both architecture and functionality. To demonstrate this potential, model simple brushes and hyperbranched examples were prepared. SCNP with the hyperbranched motif were remarkably dense, a result which demonstrates the potential to facilitate more globular SCNP structures using modifications of intrachain polymerizations. Methacrylic brush arms, which are not non-ATRC active, could be induced to couple by adding 5 equivalents of styrene under the shared ATRP/C conditions. In addition, it was determined that hyperbranched SCNP retain “living” ω-ends which may be initiated to perform post-collapse polymerizations. A model styrene example is presented; despite occurring in an ultradilute solution, the polymerization maintains fidelity to pseudo-first order kinetics. In sum, there is currently a great impetus for pushing the boundaries of structural and functional complexity that can be designed using the single-chain nanoparticle motif. Atom transfer radical chemistry is a particularly versatile example and it is my hope that this work facilitates the creation of new creative and functional designs.