Crystalline polymeric materials play an increasingly important role in daily life.Understanding and controlling the development of crystallinity is integral to improving the performance of crystalline polymers in packaging, drug delivery, water treatment, gas separations, and many other industries. Herein, fluorescence and Raman spectroscopy have been applied for the first time to study the crystallinity of polymers, including traditional semicrystalline thermoplastics and covalent organic frameworks (COFs; an emerging class of crystalline polymers with highly ordered pore structures). On one hand, by incorporating a fluorescent dye segment into a semicrystalline polymer matrix, it is feasible to accurately monitor its crystallization and melting. The flexibility of dye incorporation allows for new fundamental insights into polymer crystallization in the bulk and at/near interfaces that may otherwise be out of reach for established techniques like differential scanning calorimetry (DSC). On the other hand, Raman spectroscopy has been identified as a technique sensitive to the crystallinity of COFs and applied alongside well-established characterization techniques (X-ray diffraction and N2 adsorption) to monitor the crystallization of COFs during synthesis. This has enabled careful control of COF crystallinity during solvothermal synthesis for improved application in the field of drug delivery. The monitoring of COF crystallinity has been extended to more complex film geometries produced by interfacial polymerization. The high molecular sieving potential of COFs remains out of reach in part due to a lack of understanding of the interplay between crystallinity, crystallite orientation, and filtration performance. A careful study of these relationships is suggested for future work to provide key insight toward applying COFs as molecular sieving materials in water treatment and other separation applications.

Integrating advanced materials with innovative manufacturing techniques has propelled the field of additive manufacturing into new frontiers. This study explores the rapid 3D printing of reduced graphene oxide/polymer composites using Micro-Continuous Liquid Interface Production (μCLIP), a cutting-edge technology known for its speed and precision. A printable ink is formulated with reduced graphene oxide for μCLIP-based 3D printing. The research focuses on optimizing μCLIP parameters to fabricate reduced graphene composites efficiently. The study encompasses material synthesis, ink formulation and explores the resulting material's structural and electrical properties. The marriage of graphene's unique attributes with the rapid prototyping capabilities of μCLIP opens new avenues for scalable and rapid production in applications such as energy storage, sensors, and lightweight structural components. This work contributes to the evolving landscape of advanced materials and additive manufacturing, offering insights into the synthesis, characterization, and potential applications of 3D printed reduced graphene oxide/polymercomposites.

Advancements in three-dimensional (3D) additive manufacturing techniques have opened up new possibilities for healthcare systems and the medical industry, allowing for the realization of concepts that were once confined to theoretical discussions. Among these groundbreaking research endeavors is the development of intricate magnetic structures that can be actuated through non-invasive methods, including electromagnetic and magnetic actuation. Magnetic actuation, in particular, offers the advantage of untethered operation. In this study, a photopolymerizable resin infused with Fe3O4 oxide nanoparticles is employed in the printing process using the micro-continuous liquid interface production technique. The objective is to optimize the manufacturing process to produce microstructures featuring smooth surfaces and reduced surface porosity, and enhanced flexibility and magnetic actuation. Various intricate structures are fabricated to validate the printing process's capabilities. Furthermore, the assessment of the flexibilty of these 3D-printed structures is conducted in the presence of an external magnetic field using a homemade bending test setup, allowing for a comprehensive characterization of these components. This research serves as a foundation for the future design and development of micro-robots using micro-continuous liquid interface production technique.

Polymer composite has been under rapid development with advancements in polymer chemistry, synthetic fibers, and nanoparticles. With advantages such as lightweight, corrosion resistance, and tunable functionalities, polymer composite plays a significant role in various applications such as aerospace, wearable electronics, energy storage systems, robotics, biomedicine, and microelectronics. In general, polymer composite can be divided into particulate-filled, fiber-filled, or network-filled types depending on the manufacturing process and internal structure. Over the years, fabrication processes on the macro- and micro-scales have been extensively explored. For example, lamination, fiber tow steering, and fiber spinning correspond to meter, millimeter, and micrometer scales, respectively. With the development of nanoparticles and their exceptional material properties, polymer nanoparticle composite has shown promising material property enhancements. However, the lack of economical solutions to achieve nanoscale nanoparticle morphology control limits the reinforcement efficiency and industrial applications. This dissertation focuses on utilizing additive manufacturing as a tooling method to achieve nanoparticle morphology control in polymer nanocomposite fibers. Chapter 1 gives a thorough background review regarding fiber composite, additive manufacturing, and the importance of nanoparticle orientation. Two types of nozzle designs, concentrical and layer-by-layer, are 3D printed and combined with the dry-jet-wet fiber spinning method to create continuous fibers with internal structures. Chapters 2 to 5 correspond to four stages of my research, namely, (2) multi-material fiber spinning, (3) interfacial-assisted nanoparticle alignment, (4) microscale patterning, and (5) nanoscale patterning. The achieved feature resolution also improves from 100 µm, 10 µm, 2 µm, to 170 nm, respectively. The process-structural-property relationship of polymer nanocomposite fibers is also investigated with applications demonstrations including sensors, electrically conductive fibers, thermally conductive fibers, and mechanically reinforced fibers. At last, Chapter 6 gives a summary and some future perspectives regarding fiber composites.

Recent advancements in the field of light wavefront engineering rely on complex 3D metasurfaces composed of sub-wavelength structures which, for the near infrared range, are challenging to manufacture using contemporary scalable micro- and nanomachining solutions. To address this demand, a novel parallel micromachining method, called metal-assisted electrochemical nanoimprinting (Mac-Imprint) was developed. Mac-Imprint relies on the catalysis of silicon wet etching by a gold-coated stamp enabled by mass-transport of the reactants to achieve high pattern transfer fidelity. This was realized by (i) using nanoporous catalysts to promote etching solution diffusion and (ii) semiconductor substrate pre-patterning with millimeter-scale pillars to provide etching solution storage. However, both of these approaches obstruct scaling of the process in terms of (i) surface roughness and resolution, and (ii) areal footprint of the fabricated structures. To address the first limitation, this dissertation explores fundamental mechanisms underlying the resolution limit of Mac-Imprint and correlates it to the Debye length (~0.9 nm). By synthesizing nanoporous catalytic stamps with pore size less than 10 nm, the sidewall roughness of Mac-Imprinted patterns is reduced to levels comparable to plasma-based micromachining. This improvement allows for the implementation of Mac-Imprint to fabricate Si rib waveguides with limited levels of light scattering on its sidewall. To address the second limitation, this dissertation focuses on the management of the etching solution storage by developing engineered stamps composed of highly porous polymers coated in gold. In a plate-to-plate configuration, such stamps allow for the uniform patterning of chip-scale Si substrates with hierarchical 3D antireflective and antifouling patterns. The development of a Mac-Imprint system capable of conformal patterning onto non-flat substrates becomes possible due to the flexible and stretchable nature of gold-coated porous polymer stamps. Understanding of their mechanical behavior during conformal contact allows for the first implementation of Mac-Imprint to directly micromachine 3D hierarchical patterns onto plano-convex Si lenses, paving the way towards scalable fabrication of multifunctional 3D metasurfaces for applications in advanced optics.

Working with chocolate is a difficult endeavor. However, through the use of additive manufacturing technologies, the labor involved can be reduced. One difficulty is the pumping of the melted chocolate through the system onto the print bed of the printer. In this paper, three systems of transferring chocolate are investigated: A syringe system, a gear pump system, and an auger system. Each system is explained with a model of the proposed system and the pros and cons are discussed. Lastly, a system composed of parts of the syringe and auger system is proposed. The positive and negative aspects of this design are discussed, and a 3D model of the system is given as well. This system is suggested as a better option, and future research can be done to investigate and rate these systems in greater detail. In commercial food applications, these technologies can change the way chocolate is manipulated, and difficult practices can be simplified for home chefs.

Multi-material fabrication allows for the creation of individual parts composed of several materials with distinct properties, providing opportunities for integrating mechanisms into monolithic components. Components produced in this manner will have material boundaries which may be points of failure. However, the unique capabilities of multi-material fabrication allow for the use of graded material transitions at these boundaries to mitigate the impact of abrupt material property changes.

The goal of this work is to identify methods of creating graded material transitions that can improve the ultimate tensile strength of a multi-material component while maintaining other model properties. Particular focus is given towards transitions that can be produced using low cost manufacturing equipment. This work presents a series of methods for creating graded material transitions which include previously established transition types as well as several novel techniques. Test samples of each transition type were produced using additive manufacturing and their performance was measured. It is shown that some types of transitions can increase the ultimate strength of a part, while others may introduce new stress concentrations that reduce performance. This work then presents a method for adjusting the elastic modulus of a component to which graded material transitions have been added to allow the original design properties to be met.