NH BioMade Publications
Adenine Methylation Enhances the Conformational Flexibility of an RNA Hairpin Tetraloop
The Journal of Physical Chemistry B. doi: 10.1021/acs.jpcb.4c00522
Molecular basis for differential recognition of an allosteric inhibitor by receptor tyrosine kinases
Proteins: Structure, Function, Bioinformatics. doi: 10.1002/prot.26685
Quantitative Assessment of Energetic Contributions of Residues in a SARS-CoV-2 Viral Enzyme/Nanobody Interface
Journal of Chemical Information and Modeling. doi: 10.1021/acs.jcim.3c01933
A Protein-Adsorbent Hydrogel with Tunable Stiffness for Tissue Culture Demonstrates Matrix-Dependent Stiffness Responses
Advanced Functional Materials. doi: 10.1002/adfm.202309567
Melanin Zinc Complex as a Biocompatible Agent for Clearing Bacteremia
Advanced Materials Interfaces. doi: 10.1002/admi.202300369
Assessing strength of phases in a quadruplex high entropy alloy via high-throughput nanoindentation to clarify origins of strain hardening
Materials Characterization, 207, 113594. doi: 10.1016/j.matchar.2023.113594
Biocompatible 3D Printed MXene Microlattices for Tissue-Integrated Antibiotic Sensing
Advanced Materials Technologies. doi: 10.1002/admt.202301517
Multi-interpolation Method to Linearize Stress Path in Cruciform Specimen for In-Plane Biaxial Test
JOM. doi: 10.1007/s11837-023-06158-x
Evolution of microstructure and strength of a high entropy alloy undergoing the strain-induced martensitic transformation
Materials Science and Engineering: A, 887, 145754. doi: 10.1016/j.msea.2023.145754
Inhouse Multi-Material Nozzle System Design and Fabrication for 3D Bioprinting Process: Next Step
ASME 2023 18th International Manufacturing Science and Engineering Conference. doi: 10.1115/MSEC2023-104454
Systemic Control of 3D Bioprinting Process Parameters to Achieve Defined Scaffold Porosity
ASME 2023 18th International Manufacturing Science and Engineering Conference. doi: 10.1115/MSEC2023-104235
Controlling Rheological Properties of Hybrid Hydrogel Using Short Fiber for Extrusion-Based 3D Bioprinting Process
ASME 2023 18th International Manufacturing Science and Engineering Conference. doi: 10.1115/MSEC2023-104233
Field fluctuations viscoplastic self-consistent crystal plasticity: Applications to predicting texture evolution during deformation and recrystallization of cubic polycrystalline metals
Acta Materialia, 261, 119395. doi:10.1016/j.actamat.2023.119395
An Investigation on 3D Bio-Printed Scaffold Shape Fidelity Incubated in a Custom-Made Perfusion Bioreactor
ASME 2023 18th International Manufacturing Science and Engineering Conference. doi: 10.1115/MSEC2023-104321
Fluid Flow Analysis for Suitable 3D Bio-Printed Scaffold Architectures to Incubate in a Perfusion Bioreactor: A Simulation Approach
ASME 2023 18th International Manufacturing Science and Engineering Conference. doi: 10.1115/MSEC2023-104324
Inter-void shearing effect on damage evolution under plane strain deformation in high-strength aluminum alloy sheet
Journal of Materials Research and Technology. doi: 10.1016/j.jmrt.2023.09.079
Development of Single-Crystalline and 3D-Printable Porous Organic Materials
Submitted to Dartmouth College in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Porous organic materials with designable structures, large surface areas, low densities, and unique electronic and optical properties have found widespread applications in adsorption, separation, energy storage, and catalysis. However, the majority of organic porous materials are synthesized as fluffy powders, which poses two fundamental challenges for them. Firstly, they lack a single-crystal structure at the microscopic scale, making it difficult to study the specific pore size, shape, and potential substrate binding sites at the atomic level and further establish the structure-property relationship. Secondly, they lack the general processing method and macroscopic shape design, making it difficult to manufacture suitable components for specific applications in real-world settings. Such deficiencies can also potentially impact the material's mass transfer efficiency and other performance aspects. In this thesis, based on my research on porous organic materials, I propose my thoughts and design to help solve the two challenges mentioned.
Firstly, I discussed why we need single crystals and how to synthesize a single-crystalline covalently connected framework. (1) I present examples of the fundamental study of host-guest and guest-guest interactions of multiple guest molecules within a hydrogen-bonded organic framework (HOF) through single-crystal structure analysis. (2) Using our group's unique method for designing hydrogen-bonded cross-linked organic frameworks (HCOFs), I demonstrate the synthesis of single-crystal ionic HCOF-7 with halogen bonding and anion exchanging active sites, which is utilized for both I2 and I- at high temperatures.
Second, I introduce 3D-printing technology to fabricate porous organic materials with macroscopic structures. (1) For the first time, I describe a general method for largescale synthesis of 3D-printable imine-based covalent organic frameworks (COFs) using the hierarchical self-assembly enabled template synthesis. (2) I discovered that the template synthesis-based 3D printing technique could also be employed for the fabrication of covalently cross-linked amorphous porous polymers with nano-tubular cavities, which could be used for highly efficient natural product separation.
Overall, by integrating knowledge from different fields, I aim to help connect the micro to the macro and establish bridges between the molecular design, materials properties, and real-life application of porous organic materials.
Inducing an LCST in hydrophilic polysaccharides via engineered macromolecular hydrophobicity
Scientific Reports doi: 10.1038/s41598-023-41947-z
Investigation of Temperature and Deformation Path Effects on Induced Martensite Transformation of SS304L During Double-Sided Incremental Forming
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:
Incremental sheet forming (ISF) was invented to make sheet metal manufacturing more flexible, enabling rapid prototyping. However, it was initially plagued with inaccurate tolerances. With the advent of double-sided incremental forming (DSIF) more accurate sheet metal parts are capable and thus has received more interest from industry in recent years. In this thesis, the effects of both temperature control, using a vortex tube with compressed shop air, and deformation path, utilizing a reverse, reforming sequence, have on the strain induced γ-austenite to a’-martensite phase transformation in stainless steel 304L (SS304L) during double sided incremental forming were studied on a pyramidal geometry. The results show that reducing the temperature of the SS304L during deformation increases the achievable a’-martensite volume fraction (MVF), which corroborates past research findings. The study also demonstrates that implementing the reforming process increases the MVF, achieving ~90% transformation along the entire formed wall when the temperature is reduced. The ability to manipulate the γ-austenite to a’-martensite transformation from <10% to ~90% by controlling these two parameters demonstrates the ability to tailor the final material properties during incremental forming for the given application.
Affecting Martensitic Transformation and Residual Stress Development Through Stress Superposition and Incremental Forming
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.
Non-Equilibrium Multiphase Particle Morphologies: Synthesis, Functionalization & Modeling
Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Waterborne technology highlights the advantage of using water as the dispersed media to replace the need for organic solvents. Emulsion polymerization is one of the most important techniques to produce functional polymer colloids of industrial importance. Besides the choice of monomers in the reaction, composite particle morphology significantly influences the mechanical properties of the materials in the applications of architectural coatings, adhesives, printing inks, and impact-resistant plastics. Generally, emulsion polymerization produces spherical particles in the presence of water due to surface tension forces. In seeded emulsion polymerization, composite particles containing two incompatible phases can lead to various anomalous structures in either an equilibrium state (thermodynamic control) or a non-equilibrium state (kinetic control). Both oligomer diffusion and polymer diffusion after termination dictate the process of morphological transition. Non-equilibrium states usually describe the structure restricted by polymer diffusion without achieving the lowest energy configuration. The diffusion coefficient during the reaction is not constant but dynamically changes in response to the varying reaction conditions. Morphology control in a non-equilibrium state remains an essential subject of study, as it has yet to be fully understood. This thesis primarily focuses on the mechanistic perspective of non-equilibrium morphology by investigating polymer diffusion and oligomer radial penetration in local conditions. The aim is to establish guidelines and methods in morphology prediction.
In seeded emulsion polymerization, glassy preseeds (Tg,seed ≫ Trxn) limit the diffusion of incoming oligomers resulting in the formation of second-stage polymers in the outer region of the composite particles due to high internal viscosity. Although non-spherical particles (lobed particles) in the system of poly(methyl methacrylate)/poly(hexyl methacrylate-co-styrene)(P(MMA)/P(HMA-co-STY)) was previously reported, the detailed mechanism and their morphological features have not been fully explored. Several possible morphological features are revealed, and relevant parameters are determined. The size of the particles and the weight ratio of the 1st and 2nd stage polymer significantly impact the structure. Through the post-annealing process, it is feasible to achieve a non-equilibrium morphology with a controlled number of lobes on the surface of the particle. On the other hand, a dynamic simulation approach was established to predict radical diffusion behaviors when radical penetration is allowed. The simulated results, including thermal properties (Tg) and morphological features, agree with the experimental observations reported in the literature.
Lastly, the applications of functional polymer colloids were investigated in seeded emulsion polymerization. The 3D porous scaffold was produced through the assembly of multilobed particles. The findings indicate that the non-spherical nature of particles effectively promotes porosity compared to spherical particles. Furthermore, catechol-functionalized adhesives were successfully synthesized with a carefully selected monomer pair under a starved condition. A high-conversion latex is obtained without any side reaction with the presence of oxidizing agents in the radical polymerization.
Porous Self-Assemblies Mediated by Dumbbell Particles as Cross-Linking Agents
Journal of Chemical Theory and Computation doi: 10.1021/acs.jctc.3c00406
Reinforced double-threaded slide-ring networks for accelerated hydrogel discovery and 3D printing
Chem doi: 10.1016/j.chempr.2023.07.020
Examination of Bending Stress Superposition Effect on Martensite Transformation in Austenitic Stainless Steel 304
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.
Direct Integration of 3D Printing and Cryogel Scaffolds for Bone Tissue Engineering
Bioengineering. doi: 10.3390/bioengineering10080889
Mechanism of Ligand Discrimination by the NMT1 Riboswitch
Journal of Chemical Information and Modeling. doi: 10.1021/acs.jcim.3c00835
Coupling of conformational dynamics and inhibitor binding in the phosphodiesterase‐5 family
Protein Science doi: 10.1002/pro.4720
Characterization and modeling of carbon black/ultra- high-molecular-weight-polyethylene nanocomposites manufactured with equal channel angular extrusion
AIP Conference Proceedings. doi: 10.1063/5.0145202
Modeling the multiaxial fracture behavior of Ti–6Al–4V alloy sheets at a high temperature using improved damage modeling
Journal of Materials Research and Technology doi: 10.1016/j.jmrt.2023.06.059
A Simulation Approach to Determine Internal Architecture of 3D Bio-Printed Scaffold Suitable for A Perfusion Bioreactor
Proceedings of the IISE Annual Conference & Expo 2023.
Controlling Porosity of 3D Bioprinted Scaffold: A Process Parameter-Based Approach
Proceedings of the IISE Annual Conference & Expo 2023.
Tuning Process Parameters for Multi-Material Extrusion Through In-house Nozzle System for 3D Bio-printing Process
Proceedings of the IISE Annual Conference & Expo 2023.
Influence of Short Fiber Encapsulated in Hybrid Hydrogel For 3d Bioprinting Process: Aspect of Rheological Properties
Proceedings of the IISE Annual Conference & Expo 2023.
Identifying Suitable Three-Dimensional Bio-Printed Scaffold Architectures to Incubate in a Perfusion Bioreactor: Simulation and Experimental Approaches
Journal of Medical Devices doi: 10.1115/1.4062492
Cyclodextrin Impedimetric Biosensors for the Detection of Hydrophobic Metabolites
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.
Supramolecular Design of 3D-printable Hydrogels for Functional Materials
Submitted to Dartmouth College in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Additive manufacturing, more commonly known as 3D-printing, is bringing about a grand technological transformation in material design and fabrication. In contrast to traditional fabrication techniques, 3D-printing features rapid prototyping, complex and customized 3D structural designs, and multi-material integration. Among current 3D-printing systems, direct-ink-writing (DIW) exhibits unique functionalities due to its mild operation conditions and the ability to integrate various organic and inorganic entities. Although supramolecular binding motifs are increasingly utilized in 3D-printing designs, the optimization of 3D-printable inks remains largely empirical. In this thesis, we present two strategies to rationally design supramolecularly crosslinked 3D-printable hydrogels, including (1) micro-crystallization and (2) hierarchical co-assembly-enabled DIW 3D-printing. We also highlight the follow-up applications using either of the strategies and the design principles when aiming for a specific purpose.
First, we designed a 3D-printable hydrogel using the micro-crystallization of polypseudorotaxanes via kinetic trapping. The installation of stoppers and/or speed bumps on polymer chain ends enabled the formation of kinetically trapped polypseudorotaxane networks suitable for DIW 3D-printing. We systematically studied the assembly between polyethylene glycol (PEG) and α-CD and established a clear structure-property relationship. Harnessing the kinetic trapping characteristic, we designed 3D-printed heterostructures composed of two polyrotaxane networks, which were able to shape morph upon moisture variations.
Second, we applied the kinetic trapping principles to design 3D-printable pro-slide-ring crosslinker hydrogels composed of PEG and γ-CD. The supramolecularly crosslinked hydrogels were thereafter converted to crystalline-domain-reinforced slide-ring materials. Here, the micro-crystallization not only enabled 3D-printing but also reinforced the hydrogel material in terms of rigidity. The slide-ring cross-linkages and the crystalline domains overcame the trade-offs between toughness and elasticity, with the structure-property relationship elucidated through high-throughput synthesis and machine learning. The hydrogels were fabricated into high-performance capacitive stress sensors to demonstrate their excellent mechanical properties and material versatility.
Third, we introduced our efforts of using the hierarchical co-assembly strategy to develop 3D-printable 1,3,5-tricarboxamide (BTA) materials. We designed and synthesized 12 BTA monomers and employed them for two applications, including liquid crystalline materials for optical property modulations and the construction of tough hydrogel materials. Molecularly, we studied the self-assembly and co-assembly of BTA motifs, particularly in a crosslinked network. Macroscopically, we synthesized BTA-based crosslinked networks for optical and mechanical property investigations to correlate the structural information molecularly. We also demonstrated the construction of 3D-printed BTA materials, exhibiting superior features compared to materials synthesized in bulk.
Gelatin-Based Microporous Injectable Hydrogels For In Situ Stem Cell Encapsulation
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:
In this dissertation, I developed and investigated gelatin-based microporous injectable hydrogels for the encapsulation of stem cells for multiple applications in cell delivery. Utilizing microgels composed from a mixture of gelatin and modified gelatin, I demonstrated the utility of a dual crosslinking mechanism, which enabled rapid gelation and tissue adhesion with improved cytocompatibility. Mesenchymal stem cells (MSCs) encapsulated in this hydrogel proliferated at a more rapid rate than in a nonporous counterpart, and showed increased immunomodulatory potential. Then, I investigated gelatin microporous hydrogel for the encapsulation of MSCs for bone tissue regeneration. Encapsulated cells more readily differentiated into osteoblasts (i.e. boneforming cells) in the microporous environment observed by morphological changes and quantitative assays. This is believed to be due to enhanced cell spreading and cell-cell communication in the unique 3D environment provided to the cells by the microporous hydrogel. Transcriptomic analysis was performed by mRNA sequencing (RNA-seq) of MSCs encapsulated in the differing 3D microenvironments. Results indicated that the 3D environment influenced the expression of genes that are related to cell adhesions, cell-cell interactions, cytoskeletal organization, and matrix remodeling, in addition to MSC differentiation. Because neuronal development is highly dependent on cell-cell communication, I encapsulated an established neural stem cell line (ReNcell) in gelatin microporous hydrogel to investigate neuronal differentiation in comparison to a nonporous analog. Laminin was chemically conjugated to microgel surfaces, which controlled the organization of encapsulated cells in the hydrogel environment. Cell differentiation was examined by immunofluorescence staining, and JC-1 assay was utilized to examine mitochondrial membrane polarization. The microporous hydrogel xii induced substantially greater cell spreading, morphological changes and cell-cell connections than nonporous hydrogel. The majority of the cells in the microporous hydrogel differentiated into neural lineages, evidenced by immunostaining by MAP2 and GFAP. In summary, this work demonstrates the utility of gelatin microporous injectable hydrogels for applications in in situ cell encapsulation and stem cell delivery for tissue regeneration.
Manipulating martensite transformation of SS304L during double-sided incremental forming by varying temperature and deformation path
CIRP Annals doi: 10.1016/j.cirp.2023.04.015
Hierarchically Templated Synthesis of 3D-Printed Crosslinked Cyclodextrins for Lycopene Harvesting
Small doi: 10.1002/smll.202300323
Mismatch in Nematic Interactions Leads to Composition-Dependent Crystal Nucleation in Polymer Blends
Macromolecules doi: 10.1021/acs.macromol.2c02378
Nanoparticles in Joint Arthroplasties
Nano LIFE doi: 10.1142/S1793984423300017
CD-MOF-1 for CO2 Uptake: Remote and Hybrid Green Chemistry Synthesis of a Framework Material with Environmentally Conscious Applications
Journal of Chemical Education doi: 10.1021/acs.jchemed.2c00922
Advanced supramolecular design for direct ink writing of soft materials
Chemical Society Reviews doi: 10.1039/D2CS01011A
Low generational cystamine core PAMAM derivatives modified with nuclear localization signal derived from lactoferrin as a gene carrier
Korean Journal of Chemical Engineering doi: 10.1007/s11814-022-1293-y
Role of Dynamics and Mutations in Interactions of a Zinc Finger Antiviral Protein with CG-rich Viral RNA
Journal of Chemical Information and Modeling doi: 10.1021/acs.jcim.2c01487
Tuning Shear Thinning Factors of 3D Bio-Printable Hydrogels Using Short Fiber
Materials doi: 10.3390/ma16020572
Self-Assembly in an Experimentally Realistic Model of Lobed Patchy Colloids
ACS Applied Bio Materials doi: 10.1021/acsabm.2c00910
Fabrication of Multifunctional Electronic Textiles Using Oxidative Restructuring of Copper into a Cu-Based Metal–Organic Framework
Journal of the American Chemical Society doi: 10.1021/jacs.2c05510
Epitaxial Self-Assembly of Interfaces of 2D Metal–Organic Frameworks for Electroanalytical Detection of Neurotransmitters.
ACS Nano. doi: 10.1021/acsnano.2c02529
Machine learning-based multi-objective optimization for efficient identification of crystal plasticity model parameters.
Computer Methods in Applied Mechanics and Engineering. doi: 10.1016/j.cma.2022.115740
Single-Crystalline Hydrogen-Bonded Crosslinked Organic Frameworks and Their Dynamic Guest Sorption.
Accounts of Materials Research. doi: 10.1021/accountsmr.2c00173
Sensor technologies for quality control in engineered tissue manufacturing
Biofabrication doi: 10.1088/1758-5090/ac94a1
A multiscale computational framework for wear prediction in knee replacement implants.
Mechanics of Materials. doi: 10.1016/j.mechmat.2022.104480
Double Interpolation to Achieve Linear Strain Path for AISI 1008 Steel Cruciform Specimen
ASME 2022 17th International Manufacturing Science and Engineering Conference doi: 10.1115/MSEC2022-85595
Replicating Nature: Functional and Morphological Biomimicry as Blueprints for Synthetic Macromolecular Structures
Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
The aim of this dissertation is to provide insight into synthetic materials that replicate the function and structure of natural materials. First, a comprehensive overview of the challenges and recent advances in tailored synthetic molecular recognition through molecularly imprinted polymers (MIPs) will be presented. Chapter 2 of this work discusses the synthesis of azlactonebased homopolymers as functional polymers tuned for the detection of opioid molecules. Through the rapid and efficient ring-opening reaction of azlactone pendant chains with primary amines, customized functionalization of the homopolymers with receptor-like moieties was achieved post-polymerization. Chapter 3 explores the use of functionalized diblock copolymers as protein mimics for single-chain nanoparticle (SCNP) collapse. The collapse was successful by use of a newer, one-pot deprotection and coupling Sonogashira-like reaction without coppercatalyst. The polymers and associated nanoparticles were analyzed by size-exclusion chromatography equipped with a multi-angle light scattering (SEC-MALS) detector. Shifts in retention time from polymer to nanoparticle was indicative of change in hydrodynamic volume, suggesting that the polymer was folded into SCNP. Chapter 4 investigates the use of functionalized diblock copolymers with Diels—Alder reaction compatible monomers to form SCNP. Like Chapter 4, shifts in the retention time were observed between polymer and nanoparticle, and SCNP formation discussed.
What Most Facilitates Thriving for Undergraduate Engineering Students? A Rank Order Investigation of Engineering Experts.
Proceedings of the ASEE 2022 Annual Conference. https://peer.asee.org/41107
Efficient and robust stress integration algorithm for anisotropic distortional hardening law under cross-loading with latent hardening.
European Journal of Mechanics - A/Solids, 96, 104775. doi: 10.1016/j.euromechsol.2022.104775
Designing an Interchangeable Multi-Material Nozzle System for the 3D Bioprinting Process.
Journal of Medical Devices. doi: 10.1115/1.4055249
Structural models of viral insulin‐like peptides and their analogs. Proteins: Structure, Function, and Bioinformatics.
Portico. doi: 10.1002/prot.26410
Nanostructured Cyclodextrin-Mediated Surface for Capacitive Determination of Cortisol in Multiple Biofluids
ACS Applied Materials & Interfaces, 14(37), 42374–42387. doi: 10.1021/acsami.2c07701
Effect of pyrolysis parameters on mechanical properties of polymer-derived ceramics
International Journal of Computational Materials Science and Engineering doi: 10.1142/S2047684122500154
Role of Mutations in Differential Recognition of Viral RNA Molecules by Peptides
Journal of Chemical Information and Modeling, 62(14), 3381–3390. doi: 10.1021/acs.jcim.2c00376
Self-Assembly in Mixtures of Charged Lobed Particles
Frontiers in Physics doi: 10.3389/fphy.2022.936385
Crystal plasticity modeling of strain-induced martensitic transformations to predict strain rate and temperature sensitive behavior of 304 L steels: Applications to tension, compression, torsion, and impact.
International Journal of Plasticity, 156, 103367. doi: 10.1016/j.ijplas.2022.103367
Energy dissipation pathway control in polymer derived ceramic (PDC) composites
Journal of Dynamic Behavior of Materials. doi: 10.1007/s40870-022-00344-9
Protocol for deposition of conductive oxides onto 3D-printed materials for electronic device applications
STAR Protocols. doi: 10.1016/j.xpro.2022.101523
A wearable graphene transistor-based biosensor for monitoring IL-6 biomarker
Microelectronic Engineering doi: 10.1016/j.mee.2022.111835
Superposing tensile stresses into single point incremental forming to affect martensitic transformation of SS304
IOP Conference Series: Materials Science and Engineering doi: 10.1088/1757-899x/1238/1/012085
A Roadmap to Fabricate Geometrically Accurate Three-Dimensional Scaffolds CO-Printed by Natural and Synthetic Polymers.
Journal of Micro and Nano-Manufacturing doi:10.1115/1.4055474
Rheological Investigation of Pre-Crosslinked Hybrid Hydrogels for 3D Bio-printing Processes
Proceedings for IISE Annual Conference & Expo 2022
Fast-Curing Injectable Microporous Hydrogel for In Situ Cell Encapsulation
ACS Applied Bio Materials doi: 10.1021/acsabm.2c00214
Customizable molecular recognition: advancements in design, synthesis, and application of molecularly imprinted polymers
Polymer Chemistry doi: 10.1039/D1PY01472B
Molecular interactions and inhibition of the SARS-CoV-2 Main Protease by a Thiadiazolidinone derivative
Proteins: Structure, Function, and Bioinformatics doi: 10.1002/prot.26385
Plastic anisotropy evolution of SS316L and modeling for novel cruciform specimen.
International Journal of Mechanical Sciences doi: 10.1016/j.ijmecsci.2022.107663
Inducing <111> texture in AA5182-O through continuous-bending-under-tension and recovery heat treatment processes to influence r-values
CIRP Annals doi: 10.1016/j.cirp.2022.04.059
Plasticity Characterization by Deriving Non-Linear Displacements for In-Plane Biaxial Cruciform Testing
Submitted to the University of New Hampshire in Patrial Fulfillment of the Requirements of the Degree of Master of Science in Mechanical Engineering.
THESIS ABSTRACT:
In-plane biaxial testing using a cruciform type specimen is a useful experimental method to characterize the elasto-plastic material behavior under non-uniaxial conditions. Different stress states can be imposed to the specimen simply by varying loading ratios along two orthogonal axes. Experiments can be performed using one experimental setup and one specimen geometry. Among different control options for loading, the displacement control in each arm is a stable and consistent option to keep the static deformation rate. However, a non-linear relationship exists between the control parameter e.g., displacement, and derived quantities, e.g., stress and strain. Therefore, it is a challenge to achieve desired deformation paths in the main deformation area of the specimen. In this document, an interpolation method to systematically determine nonlinear displacement paths is implemented using the finite element simulation method to produce linear stress and strain paths in the center of a cruciform specimen geometry. Interpolation is first applied to an AISI 1008 steel specimen, in which a previously interpolated linear strain path is improved with another iteration of interpolation. Interpolation is then expanded to produce displacement paths resulting in linear stress paths, having a constant stress triaxiality, for five different stress states of a SS304L cruciform specimen. The versatility of the interpolation method is displayed through the successful implementation for both strain and stress linearization as well as with two different materials and two specimen geometries.
Microstructural and Mechanical Property Characterization of Ultra-High Molecular Weight Polyethylene and its Composites Subjected to Equal Channel Angular Pressing
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.
N-Heterocyclic Carbene Functionalized Single-Chain Nanopartcles Aqueous Catalytic Platform
Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Single-chain nanoparticles (SCNP) are a class of intramolecular cross-linked polymeric nanoparticles with a variety of applications including catalysis, sensors, nanomedicine, and nanoreactors. Such nanoparticles are synthesized by folding or collapsing single polymer molecules. By implementing a single-chain folding technique, the single-chain nanoparticles with uniform degrees of cross-linking are synthesized by parent polymer chains with similar chain lengths and polymer microstructure. Polymer chains that are synthesized by various controlled polymerization techniques can be converted to SCNPs through a variety of covalent chemistry and supramolecular interactions. Based on the expected cross-linking chemistry, related functional groups can be installed either during monomer synthesis or post-polymerization functionalization by utilizing a variety of methodologies. With the goal of effecting catalysis of various organic reactions in aqueous system, we developed a series of ligand functionalized SCNPs with water-soluble pendent groups. N-heterocyclic carbene (NHC) ligands were designed and synthesized to immobilize transition metal cation on SCNPs for catalysis. By employing polymer functionalization strategy, amine-ended ligands, water soluble pendent groups, and cross-linkers were installed by substitution reaction on poly xii (pentafluorophenyl acrylate) (PFPA) synthesized by reversible addition fragmentation transfer polymerization (RAFT), and the process of reaction can be monitored by F19 NMR conveniently. Moreover, to realize inverse temperature dependent controlling, the temperature sensitive watersoluble pendent groups were utilized, such as N-isopropyl amide, which can be installed by the addition of isopropylamine in the process of functionalization of poly (PFPA). Consequently, a variety of organic reactions could be possible in aqueous system catalyzed by combination of different transition metal cations and water-soluble NHC-functionalized SCNP platform.
Rational Design and Synthesis of Antifreeze-Protein Inspired Polymers for Anti-Icing Coatings and Cryopreservation Applications
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.
Melanin Pigments as Antibacterial Agents
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:
In this dissertation I investigated the structural properties of melanin biopigment from different sources as an antibacterial and endotoxin bonding agent. I extracted melanin from Equus ferus hair with acid hydrolysis (termed EquusMel) and characterized it by microscopic and spectroscopic techniques. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that EquusMel is mainly elliptical in shape with a mesoporous and layered structure within the individual particles. Wide-angle (WAXS) and small-angle (SAXS) Xray scattering measurements demonstrated a semicrystalline multilayered structure with order spacing of 45.2 Å. Pore size distribution determined by the Barrett–Joyner–Halenda (BJH) method showed primary pores within the range of 30–50 Å. Nitrogen adsorption–desorption isotherms exhibited a Brunaur–Emmett–Teller (BET) surface area of 3 m2 /g. Raman, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) spectra revealed similar chemical signature between EquusMel and synthetic melanin (SynMel). I investigated the antibacterial effect and its mechanism of action for EquusMel. I found that EquusMel has distinct antibacterial activity due to its potential to generate reactive oxygen species (ROS). ROS generated via oxidation of catechols is considered the main mechanism of antibacterial activity. The simplicity of EquusMel extraction and its antibacterial property allows this biomaterial to be xvi applicable to a variety of areas. Zinc cations (Zn2+) were loaded on melanin structure (Mel-Zn) for rapid and selective separation of gram-negative bacteria and lipopolysaccharide (LPS) from blood. Mel-Zn was characterized by XPS and Raman which revealed the successful Zn2+ loading. I identified that Mel-Zn rapidly captures approximately 90% of Escherichia coli in whole blood and 100% of LPS in PBS, which can reduce bacteremia loads and mitigate the spread of these infectious agents to other tissues and organs. Additionally, simultaneous binding to bacteria and LPS could enhance the efficacy of antibiotic therapy. Adsorption of protein from individual protein model solutions, as well as LPS-spiked protein solutions, was found to be minimal. Hemolysis and coagulation assays demonstrate the blood biocompatibility of Mel-Zn, which could be adapted for clinical use in an extracorporeal membrane to remove pathogens and LPS in acute sepsis patients.
Water-soluble reversible addition-fragmentation chain transfer (RAFT) agents and their bioconjugation to dsDNA
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.
Coupling of a multi-GPU accelerated elasto-visco-plastic fast Fourier transform constitutive model with the implicit finite element method
Computational Materials Science doi: 10.1016/j.commatsci.2022.111348
Physical Modification of Hybrid Hydrogels to Fabricate Full-Scale Construct Using Three-Dimensional Bio-Printing Process
Journal of Micro and Nano-Manufacturing doi: 10.1115/1.4055230
Healthcare data analytics for wearable sensors
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
Transforming 3D-printed mesostructures into multimodal sensors with nanoscale conductive metal oxides
Cell Reports Physical Science doi: 10.1016/j.xcrp.2022.100786
Shear enhancement of mechanical and microstructural properties of synthetic graphite and ultra-high molecular weight polyethylene carbon composites
Journal of Applied Polymer Science doi: 10.1002/app.52175
Tunable Multilobe Particle Geometry by Annealing-Assisted Emulsion Polymerization
ACS Applied Polymer Materials. doi: 10.1021/acsapm.1c01312
3D Bio-Printability of Hybrid Pre-Crosslinked Hydrogels
International Journal of Molecular Sciences. doi: 10.3390/ijms222413481
Probing secondary coordination sphere interactions within porphyrin-cored polymer nanoparticles
Polymer Chemistry. doi: 10.1039/D1PY01005K
Conductive Stimuli-Responsive Coordination Network Linked with Bismuth for Chemiresistive Gas Sensing
ACS Applied Materials & Interfaces doi: 10.1021/acsami.1c14453
Bimetallic TwoDimensional MetalOrganic Frameworks for Chemiresistive Detection of Carbon Monoxide
Angewandte Chemie International Edition. doi: 10.1002/anie.202113665
Covalent organic frameworks as multifunctional materials for chemical detection
Chemical Society Reviews doi: 10.1039/d1cs00600b
Unraveling the Electrical and Magnetic Properties of Layered Conductive Metal Organic Framework With Atomic Precision
Angewandte Chemie International Edition. doi: 10.1002/anie.202113569
The Role of Surface Chemistry in Electroanalysis with Conductive Two-Dimensional Framework Materials
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.
Water Dynamics in a Peptide-appended Pillar[5]arene Artificial Channel in Lipid and Biomimetic Membranes
Frontiers in Chemistry. doi: 10.3389/fchem.2021.753635
Role of salt-bridging interactions in recognition of viral RNA by arginine-rich peptides
Biophysical Journal. doi: 10.1016/j.bpj.2021.10.007
Modeling of Phase Transition in Fabrication of Polymer-Derived Ceramics (PDCS)
International Journal of Computational Materials Science and Engineering. doi: 10.1142/s2047684121500329
Self-Assembly of Porous Structures From a Binary Mixture of Lobed Patchy Particles
Frontiers in Physics. doi: 10.3389/fphy.2021.767623.
Structures and interactions of insulin-like peptides from cone snail venom
Proteins. doi: 10.1002/prot.26265
Conformational dynamics and energetics of viral RNA recognition by lab-evolved proteins
Physical Chemistry Chemical Physics. doi: 10.1039/d1cp03822b
Recent Advances in Non-Enzymatic Electrochemical Detection of Hydrophobic Metabolites in Biofluids
Sensors and Actuators Reports. doi: 10.1016/j.snr.2021.100051.
Design of 3D-Printable Cyclodextrin-Based Poly(pseudo)rotaxane Materials
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.
Effects of plasticity-induced martensitic transformation and grain refinement on the evolution of microstructure and mechanical properties of a metastable high entropy alloy
Journal of Alloys and Compounds. doi: 10.1016/j.jallcom.2021.161871.
A surprisingly gentle approach to cavity containing spherocylindrical microparticles from ordinary polymer dispersions in flow
Materials Horizons. doi: 10.1039/d1mh01108a.
A Heteromeric Carboxylic-acid-based Single Crystalline Crosslinked Organic Framework
Angewandte Chemie International Edition. doi: 10.1002/anie.202109987
Micromechanical origins of remarkable elongation-to-fracture in AHSS TRIP steels via continuous bending under tension
Materials Science and Engineering: A. doi: 10.1016/j.msea.2021.141876
Rheological Analysis of Low Viscosity Hydrogels for 3D Bio-Printing Processes
Volume 1: Additive Manufacturing; Advanced Materials Manufacturing; Biomanufacturing; Life Cycle Engineering; Manufacturing Equipment and Automation. doi: 10.1115/msec2021-63658
Designing an Interchangeable Multi-Material Nozzle System for 3D Bioprinting Process
Volume 1: Additive Manufacturing; Advanced Materials Manufacturing; Biomanufacturing; Life Cycle Engineering; Manufacturing Equipment and Automation. doi: 10.1115/msec2021-63471
Numerical Analysis of SS316L Biaxial Cruciform Specimens Under Proportional Loading Paths
Volume 2: Manufacturing Processes; Manufacturing Systems; Nano/Micro/Meso Manufacturing; Quality and Reliability. doi: 10.1115/MSEC2021-59877.
Rheological Study of Highly Thixotropic Hydrogels for 3D Bio- Printing Processes
Proceedings of the 2021 IISE Annual Virtual Conference.
Phase transition in Polymer Derived Ceramics (PDCs) and its effect on mechanical response
The 12th International Conference on Computational Methods.
The Effect of Temperature on the Strain-Induced Austenite to Martensite Transformation in SS 316L During Uniaxial Tension
Forming the Future. doi: 10.1007/978-3-030-75381-8_155
Experimental Implementation of SS 316L Cruciform Testing to Achieve Various Deformation Paths
Forming the Future. doi: 10.1007/978-3-030-75381-8_166
Kinetic trapping of 3D-printable cyclodextrin-based poly(pseudo)rotaxane networks
Chem. doi: 10.1016/j.chempr.2021.06.004
Design of Functionalized Lobed Particles for Porous Self-Assemblies
JOM. doi: 10.1007/s11837-021-04715-w
Design of Functionalized Lobed Particles for Porous Self-Assemblies
JOM. doi: 10.1007/s11837-021-04715-w
Finite Element Model of Equal Channel Angular Extrusion of Ultra High Molecular Weight Polyethylene
Journal of Manufacturing Science and Engineering. doi: 10.1115/1.4051189
Modeling of plasticity-induced martensitic transformation to achieve hierarchical, heterogeneous, and tailored microstructures in stainless steels
CIRP Journal of Manufacturing Science and Technology. doi: 10.1016/j.cirpj.2021.04.006
Mechanistic Insights Into Relationship Between Network Architecture, Polymerization Kinetics, And Macromolecular Properties
Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Given the rising of environmental concern, the market of waterborne coating and adhesives has been constantly growing. Polymer latex particles produced by emulsion polymerization are one type of important components in their formulations. Thus, to tune mechanical properties of waterborne coatings and adhesives, one of the common ways is to utilize crosslinkers to form a macromolecular network structure, as known as “gel”, inside of the polymer latex. A major challenge to obtain desired properties of the material is how to control macromolecular architecture, such as sol-gel ratio and crosslinking density. Hence, this dissertation focuses on the study of predicting and controlling macromolecular network architectures in both bulk polymerization and emulsion polymerization. Bulk polymerizations share some similar mechanisms with emulsion polymerization but is simplified by being a homogeneous single phase reaction environment. Emulsion polymerization is a heterogeneous reaction environment with reactions in two phases. Due to the complexity of the emulsion polymerization environment, bulk polymerization is often used xxii as a first test environment to simplify and study new reaction systems. Based on our previous work, a reduced reactivity parameter, Ψ, was introduced and applied to precisely describe the reactivity of crosslinking sites (pendent vinyl groups from crosslinker monomers). Most of our prior work used the bulk polymerization environment and here we now also extend to the emulsion polymerization environment. In addition to crosslinking reaction kinetics, we also explored macromolecular structure development as predicted by a hybrid Monte Carlo Model. Chapter 3 and Chapter 4 significantly extended our previous work. Chapter 3 explored a wide matrix of monomer-crosslinker pairs of varied molecular size and revealed a stronger understanding of the relationship between resulting Ψ values and the structures of each monomer-crosslinker pair. In Chapter 4, another mechanistic factor, reactivity ratio between the crosslinker and the main monomer, was also introduced. This chapter studied how both contributions, Ψ and reactivity ratio, influence the eventual crosslinking reaction. All polymerizations were conducted via bulk polymerization in Chapter 3 and Chapter 4. Emulsion polymerization is a heterophase polymerization and their polymers are known as “products by process”. Here, we fed the monomer mixture to the reaction in a semi-batch mode, and therefore, Chapter 5 mainly studied the influence of the monomer feeding profile on gel formation during emulsion polymerization. A relationship was observed that higher feeding rate can cause higher gel content. This was found to be explained by the dominance of a “micro loop” formation, an intramolecular first order reaction between the chain end radical and its own pendent vinyl group, when the unreacted free monomer concentration was very low (i.e. with slow monomer feed rate to the reactor). These microloops consumed pendent vinyls without allowing a crosslinking event to occur. At higher monomer feed rate, the mechanisms xxiii would start to favor the Ψ and reactivity ratio effects again. This was an important learning on the balance between favored mechanisms as a function of the polymerization process and environment. Chapter 6 is a side but still relevant topic. In this chapter, four different bio-based reactive surfactants were successfully synthesized. They could be used as stabilizers for emulsion polymerization. Two of four of reactive surfactants were two different types of bi-functional surfactants (divinyls, thus also considered crosslinkers). They were proved to not only be able to stabilize the particles, but also be able to crosslink the particles under certain conditions. Chapter 6 is a proof-of-concept study and should not be considered completed work. Nonetheless, it shows great promise for continuation by another student.
Micromechanical Modeling and Evaluation of Process-Induced Residual Stresses in 3D Woven Composites
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.
Role of conformational heterogeneity in ligand recognition by viral RNA molecules
Physical Chemistry Chemical Physics. doi: 10.1039/d1cp00679g
Enhanced Porosity in Self-Assembled Morphologies Mediated by Charged Lobes on Patchy Particles
The Journal of Physical Chemistry B. doi: 10.1021/acs.jpcb.0c11096
Identification of crystal plasticity model parameters by multi-objective optimization integrating microstructural evolution and mechanical data
Computer Methods in Applied Mechanics and Engineering. doi: 10.1016/j.cma.2021.113747
Thermo-hydrogen refinement of microstructure to improve mechanical properties of Ti-6Al-4V fabricated via laser powder bed fusion
Materials Science and Engineering: A. doi: 10.1016/j.msea.2021.140980
An Integrated Design of a Polypseudorotaxane‐based Sea Cucumber Mimic
Angewandte Chemie International Edition. doi: 10.1002/anie.202017019
Reaction Coordinate and Thermodynamics of Base Flipping in RNA
Journal of Chemical Theory and Computation. doi: 10.1021/acs.jctc.0c01199
On numerical modeling of equal channel angular extrusion of ultra high molecular weight polyethylene
ASME 2020 International Mechanical Engineering Congress and Exposition. doi: 10.1115/imece2020-24111
Origins of high ductility exhibited by an extruded magnesium alloy Mg-1.8Zn-0.2Ca: experiments and crystal plasticity modeling
Journal of Materials Science & Technology, doi: 10.1016/j.jmst.2020.12.047
Analytical Investigation of Varying Deformation Paths Using Microtube Inflation and Axial Tension
Proceedings of the ASME 2020 15th International Manufacturing Science and Engineering Conference. Volume 2: Manufacturing Processes; Manufacturing Systems; Nano/Micro/Meso Manufacturing; Quality and Reliability. September 3, 2020. V002T08A012. ASME. doi:10.1115/MSEC2020-8372
Allosteric Pathways Originating at Cysteine Residues in Regulators of G-Protein Signaling Proteins
Biophysical Journal, doi: 10.1016/j.bpj.2020.12.010
Experimental Investigation and Plasticity Modeling of SS316L Microtubes Under Varying Deformation Paths
Journal of Micro and Nano-Manufacturing, doi: 10.1115/1.4049364
Hierarchical Tuning of the Performance of Electrochemical Carbon Dioxide Reduction Using Conductive Two-Dimensional Metallophthalocyanine Based Metal–Organic Frameworks
Journal of the American Chemical Society, doi: 10.1021/jacs.0c07041
Coupling kinetic Monte Carlo and finite element methods to model the strain path sensitivity of the isothermal stress-assisted martensite nucleation in TRIP-assisted steels
Mechanics of Materials, 154, 103707. doi: 10.1016/j.mechmat.2020.103707
100th Anniversary of Macromolecular Science Viewpoint: Re-examining Single-Chain Nanoparticles
ACS Macro Letters, 9, 1836-1843. doi: 10.1021/acsmacrolett.0c00774
Experimental Investigation and Plasticity Modeling of SS316L Microtubes Under Varying Deformation Paths
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:
Results for SS316L microtube experiments under combined inflation and axial loading for single and multi-loading segment deformation paths are presented along with a plasticity model to predict the associated stress and strain paths. The microtube inflation/tension machine, utilized for these experiments, creates biaxial stress states by applying axial tension or compression and internal pressure simultaneously. Two types of loading paths are considered in this paper, proportional (where a single loading path with a given axial:hoop stress ratio is followed) and corner (where an initial pure loading segment, i.e., axial or hoop, is followed by a secondary loading segment in the transverse direction, i.e., either hoop or axial, respectively). The experiments are designed to produce the same final strain state under different deformation paths, resulting in different final stress states. This difference in stress state can affect the material properties of the final part, which can be varied for the intended application, e.g., biomedical hardware, while maintaining the desired geometry. The experiments are replicated in a reasonable way by a material model that combines the Hill 1948 anisotropic yield function and the Hockett-Sherby hardening law. Discussion of the ix grain size effects during microforming impacting the ability to achieve consistent deformation path results is included.
A Multi-Scale Crystal Plasticity Finite Element Modeling Framework For Predicting Strain-Rate Sensitive Deformation Of Hexagonal Metals
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.
Melanin pigments extracted from horsehair as antibacterial agents
Journal of Materials Chemistry B, doi: 10.1039/d0tb02475a
A full-field crystal plasticity model including the effects of precipitates: Application to monotonic, load reversal, and low-cycle fatigue behavior of Inconel 718
Materials Science and Engineering: A. doi: 10.1016/j.msea.2020.140478
Structural Analysis of the Regulatory GAF Domains of cGMP Phosphodiesterase Elucidates the Allosteric Communication Pathway
Journal of Molecular Biology. doi: 10.1016/j.jmb.2020.08.026
Self-assembly behavior of experimentally realizable lobed patchy particles
Soft Matter, 16, 8101-8107. doi: 10.1039/d0sm00954g
Role of Entropy in Colloidal Self-Assembly
Entropy, 22(8), 877. doi:10.3390/e22080877
Stress-assisted (γ→α′) and strain-induced (γ→ε→α′) phase transformation kinetics laws implemented in a crystal plasticity model for predicting strain path sensitive deformation of austenitic steels
International Journal of Plasticity, 136, 102807. doi: 10.1016/j.ijplas.2020.102807
Host–Guest Interactions and Redox Activity in Layered Conductive Metal–Organic Frameworks
Chemistry of Materials. doi: 10.1021/acs.chemmater.0c01007
Two-dimensional d-π conjugated metal-organic framework based on hexahydroxytrinaphthylene
Nano Research. doi: 10.1007/s12274-020-2874-x
Ligand Recognition in Viral RNA Necessitates Rare Conformational Transitions
The Journal of Physical Chemistry Letters. doi:10.1021/acs.jpclett.0c01390
Molecular Engineering of Multifunctional Metallophthalocyanine-Containing Framework Materials
Chemistry of Materials. doi: 10.1021/acs.chemmater.9b05289
Effects of heat treatment and build orientation on the evolution of ϵ and α′ martensite and strength during compressive loading of additively manufactured 304L stainless steel
Acta Materialia, 195, 59-70. doi: 10.1016/j.actamat.2020.04.036
Diels-Alder Functionalized Particles for Mechanical Improvements in Additive Manufacturing
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.
Electrically-transduced sensors based on 2D Metal–Organic Frameworks
Submitted to the Faculty in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry.
DISSERTATION ABSTRACT:
Since the discovery of electrically conductive two-dimensional (2D) metal–organic frameworks (MOFs), the synthetically tunable properties and intrinsic porosity of these materials make them promising for multifunctional sensing devices. The focus of my work is on a class of 2D MOFs based on a triphenylene core (2,3,6,7,10,11- hexahydroxytriphenylene, HHTP and 2,3,6,7,10,11-hexaiminotriphenylene, HITP) coordinating to divalent Cu or Ni metal nodes forming M3HXTP2 MOF analogs (M = Ni, Cu; X = NH, HITP or O, HHTP). Chapter 2 describes a simple strategy for device fabrication, using mechanical abrasion, enabling the chemiresistive sensing of NH3, H2S, and NO. The value in this contribution is threefold. First, the technique may be applicable to a wide range of materials, both semiconductors and possibly insulators. Second, the rapid prototyping method enables direct deposition using mechanical abrasion on a wide range of substrates. Third, the integration of the MOF-based sensing material into devices is entirely solvent-free, which can preserve device substrates sensitive to harsh solvents. Chapter 3 describes a new strategy of MOF synthesis termed oxidative restructuring that feature several innovative characteristics that advance the field of MOF integration. First, oxidative restructuring enables the facile integration of Cu3HHTP2 and Cu-BTC onto prepatterned Cu layer on multiple substrates. Second, we detail spectroscopic evidence that provides insight into the interaction between Cu3HHTP2 and NO using diffuse reflectance infrared fourier transform spectroscopy and X-ray photoelectron spectroscopy. Third, Cu3HHTP2 MOF devices demonstrated the highest dynamic loading capacity of NO and functioned as chemiresistive sensors for the detection of NO and H2S. Chapter 4 describes the implementation of 2D MOF based electrodes to enable the voltammetric detection of biologically relevant analytes. First, strategic selection of redox active analytes combined with the electrochemical methods, allowed us to investigate the intrinsic electrochemical properties of M3HXTP2 MOF analogs (M = Ni, Cu; X = NH, HITP or O, HHTP). Second, this demonstrated one of the first uses of 2D MOFs in solution phase detection with nanomolar detection at 63 ± 11 nM for dopamine and 40 ± 17 nM for serotonin. Taken together, chapters 1-4 advance the field of conductive metal–organic frameworks by providing insight in molecular engineering of MOFs that guides the iii structure property relationships to enable precise function for chemical detection and provides strategies for the strategic integration of MOFs on substrates.
Employing Conductive Metal-Organic Frameworks for Voltammetric Detection of Neurochemicals
Journal of the American Chemical Society. doi: 10.1021/jacs.9b13402
Functional Nanoassemblies with Mirror-Image Chiroptical Properties Templated by a Single Homochiral DNA Strand
Chemistry of Materials. doi: 10.1021/acs.chemmater.9b04092
Self-assembly of lobed particles into amorphous and crystalline porous structures
Soft Matter. doi:10.1039/c9sm01878f
Thermo-responsive 3D-printed polyrotaxane monolith
Polymer Chemistry. doi:10.1039/c9py01510h
Experimental and numerical investigation of continuous bending under tension processing of dual phase high strength automotive steels
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.
Conformational dynamics and interfacial interactions of peptide-appended pillar[5]arene water channels in biomimetic membranes
Physical Chemistry Chemical Physics, 2019. doi: 10.1039/c9cp04408f
Phase space and collective variable based simulation methods for studies of rare events
Molecular Simulation, 45(14-15), 1273–1284. doi: 10.1080/08927022.2019.1634268
Two-Dimensional Chemiresistive Covalent Organic Framework with High Intrinsic Conductivity
Journal of the American Chemical Society 2019 141 (30), 11929-11937. doi: 10.1021/jacs.9b03441
Shear resistance of an auxetic chiral mechanical metamaterial
International Journal of Solids and Structures, 174-175, 28–37. doi: 10.1016/j.ijsolstr.2019.06.005
Advanced Polymer Designs for Direct‐Ink‐Write 3D Printing
Chemistry – A European Journal, 25(46), 10768–10781. doi: 10.1002/chem.201900975
ATRC Processes and Architectures as Tools for Advancing the Complexity of Single-chain Polymeric Nanoparticles
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.
Hierarchical-Coassembly-Enabled 3D-Printing of Homogeneous and Heterogeneous Covalent Organic Frameworks
Journal of the American Chemical Society 2019 141 (13), 5154-5158. doi: 10.1021/jacs.9b01561
Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials
Chemical Reviews 2019 119 (1), 478-598. doi: 10.1021/acs.chemrev.8b00311