Doctor of Philosophy

dissertationEngineered materials consisting of nano- or microparticles embedded in a matrix material may exhibit unique physical properties that are attributed to the specific type, geometry, and spatial pattern of the particles. However, existing techniques for fabricating such engineered materials are limited to laboratory scale, specific materials, and/or 2D implementations. We employ ultrasound directed self-assembly (DSA), which relies on the acoustic radiation force associated with an ultrasound wave field of wavelength significantly larger than the particle size, to organize particles of any material type dispersed in a fluid medium, into a user-specified pattern over a macroscale area or volume. We first derive the dynamics of a single particle in a fluid medium subject to a one-dimensional standing ultrasound wave field. We analyze the trajectory of the particle, driven to either a node or antinode of the ultrasound wave field by the acoustic radiation force, and we show that the particle oscillates around the node of the standing wave with an amplitude that depends on the ratio of the time-dependent drag forces and the particle inertia. We then theoretically derive and experimentally implement a method for single and multidimensional ultrasound DSA, which enables manipulating the position of a single particle and organizing user-specified patterns of nano- and microparticles dispersed in a fluid medium contained within a reservoir lined with ultrasound transducers, respectively. In contrast with existing ultrasound DSA techniques, this method works for any user-specified pattern of particles within a reservoir of arbitrary geometry and ultrasound transducer arrangement. Additionally, the method accounts for all ultrasound wave reflections in the reservoir, which allows for straightforward experimental implementation of the method. Finally, we integrate ultrasound DSA with stereolithography to fabricate engineered materials layer-by-layer via stereolithography, where in each layer we organize a user-specified pattern of particles using ultrasound DSA. This process enables manufacturing macroscale 3D materials with a user-specified microstructure consisting of particles of any material. We demonstrate 3D printing macroscale multilayer engineered materials containing a Bouligand microstructure of nickel-coated carbon fibers. Additionally, we fabricate engineered materials containing a pattern of electrically conductive nickel-coated carbon fibers, which illustrates the feasibility of 3D printing structures with embedded insulated electrical wiring. This process has implications for applications including manufacturing of metamaterials, and multifunctional composite materials

Multimaterial 3D/4D Printing by Integrating Digital Light Processing and Direct Ink Writing

Driven by the growing demand of applications in robotics, electronics, biomedical devices and wearable devices, multi-material 3D printing has now become a trend to offer solutions with a wide choice of materials with various mechanical, chemical, thermal-mechanical, or electrical properties. However, it remains a challenge to find an approach, with a wide choice of materials, to realize high-resolution multi-material 3D printing efficiently. In this study, an innovative hybrid multi-material 3D printing system is developed, which integrates digital light processing (DLP), and direct ink writing (DIW). Here, DLP can efficiently provide a high-resolution matrix, with complex geometry and multicolor appearance, while DIW can add functionality to the component due to the wide choice of functional materials, such as shape memory photopolymers, conductive inks, and liquid crystal elastomers (LCE). With this hybrid 3D printing system, multicolor functional devices, circuit-embedding architectures, soft sensors, hybrid active lattices, active tensegrities, functionally graded actuators, and pure LCE lattices were successfully fabricated, showing a great prospect in the area of electronics, smart wearable devices, soft robots and actuators.Ph.D

Magnetically assembled nanoparticle structures and their effect on mechanical response of polymer nanocomposites

Magneticky řízené samo-uspořádávání v polymerních nanokompozitech je studováno v této dizertační práci. Strukturování polymerních nanokompozitů pomocí relativně slabých magnetických polí (B=0-50 mT) bylo prokázáno jako praktická metoda pro kontrolu jejích nano a mikrostruktury. Vliv intenzity magnetického pole, množství nanočástic, viskozity a času uspořádávání na výslednou strukturu byl studován v různých systémech jako fotopolymer, polyuretan nebo koloidně dispergované nanočástice v acetonu s malým množstvím rozpuštěného polymeru. Samo-uspořádané struktury – bez aplikace vnějšího magnetického pole vykazují vícekrokovou agregaci nanočástic do uskupení s komplexním tvarem. Magnetické interakce byly označené jako odpovědné za agregaci nanočástic v samo-uspořádaných systémech pomocí výpočtů energii mezi-částicových interakcí. S rostoucím magnetickým polem, magnetické nanočástice jsou rychle uspořádané do jednorozměrných částicových řetězů s vysokým aspektním poměrem a homogenní orientaci v polymerní matrici. S prodluženým časem uspořádaní, tyto struktury postupně rostou z malých submikrometrových struktur do velkých mikroskopických super struktur. Táto metoda vykazuje velký potenciál pro kontrolovanou přípravu široké škály struktur v polymerních nanokompozitech vhodných pro technologické aplikace a také pro fundamentální studie. Magneticky uspořádané polymerní nanokompozity vykazují značnou směrovou anisotropii tuhosti kompozitu nad jeho skelným přechodem přičemž, pod skelným přechodem systému není pozorován žádný efekt. Podélně orientované struktury vykazují větší příspěvek k tuhosti kompozitů. Efektivnost vyztužení vykazuje teplotně závislý průběh a maximum je pozorováno přibližně 60 °C nad skelným přechodem. Struktura magneticky uspořádaného polymerního nanokompozitu byla popsána vícero-úrovňovým hierarchickým modelem materiálu. Mikromechanika byla využitá k popisu směrově závislého vyztužení polymerních nanokompozitů a k popisu teplotně závislé tuhosti hybridních struktur složených z nanočástic a polymeru. Schopnost nést napětí, deformovat se a nenulová tuhost hybridních struktur je odpovědná za vyztužení polymerních nanokompozitů. Přítomnost polymerních přemostění mezi nanočásticemi, které přenášejí napěti skrze magnetické struktury je označená jako nezbytná pro mechanickou odezvu polymerních nanokompozitů a pro tuhost hybridních struktur.Magnetically directed self-assembly in polymer nanocomposites is studied in this dissertation thesis. Structuring of the polymer nanocomposites by application of relatively weak external magnetic fields (B=0-50 mT) has been proven to be convenient method for the control of their nano- and microstructure. The effect of the field strength, particle loading, viscosity and assembling time on the resulted structure was studied in different systems such as photopolymer, polyurethane or colloidally dispersed magnetic nanoparticles in acetone with a small amount of dissolved polymer. Self-assembled structures – without application of the external magnetic field exhibit a multi-step aggregation into nanoparticle assemblies with a complex shape. By the calculation of interaction energies between the nanoparticles, magnetic interactions were attributed to be mainly responsible for the aggregation in self-assembled systems. With an increasing magnetic field, magnetic nanoparticles are rapidly arranged into high aspect ratio one-dimensional particle chains with a homogenous orientation in the bulk polymer matrix. After prolonged assembling time, the structures gradually grow from small submicro structures to large microscopic superstructures. This method exhibits large potential to be used for controlled creation of wide variety of structures in polymer nanocomposites suitable for technological applications and/or for fundamental studies. Magnetically structured polymer nanocomposites show significant directional anisotropy of composite’s stiffness at the temperatures above glass transition of the system while there is no effect on the mechanical response in glassy state. Longitudinally oriented structures exhibit much stronger effect on the composite’s stiffness. Reinforcing effectivity exhibits temperature dependent course with a maximum obtained approximately 60 °C above glass transition. The structure of magnetically assembled polymer nanocomposites was described by multi-level hierarchic model of material. Micromechanics was used to address the orientation dependent reinforcement and temperature dependent stiffness of the hybrid nanoparticle-polymer structures. Load carrying capability, deformation and non-zero stiffness of the hybrid structures were attributed to be responsible for the reinforcement of the polymer nanocomposites. The presence of polymer bridges between nanoparticles transmitting the stress through the magnetic structures is proposed to be essential for the mechanical properties of polymer nanocomposites and for stiffness of the hybrid structures.

Extrusion-based Direct Write of Functional Materials From Electronics to Magnetics

New micro- and nanoscale fabrication methods are of vital importance to drive scientific and technological advances in electronics, materials science, physics and biology areas. Direct ink writing (DW) describes a group of mask-less and contactless additive manufacturing (AM), or 3D printing, processes that involve dispensing inks, typically particle suspensions, through a deposition nozzle to create 2D or 3D material patterns with desired architecture and composition on a computer-controlled movable stage. Much of the functional material printing and electronics area remains underdeveloped for this new technology. There is a need to understand and establish the advantages and shortcomings of extrusion-based DW over other AM technologies for various applications. Further, the integration of extrusion DW with other AM technologies, such as stereolithography (SLA), remains an active area of research. In this study, we performed a comprehensive study of the relationships between ink properties/machine parameters and the printed line dimensions, including parametric studies of the machine parameters, an in-nozzle flow dynamics simulation, and a preliminary 3D comprehensive flow dynamics simulation. We explored the boundary and possibilities of extrusion-based DW. We pushed the limit of DW printing resolution, solid content of nonspherical particles, and printed polymer-bonded magnets with the highest density and magnetic performance among all 3D printing magnet techniques. We optimized the design of DW ink from rheological, mechanical, and microscopic perspectives. We are one of the first experimentalists as of author’s knowledge to perform bimodal highly concentrated suspension rheology analysis using nonspherical particles. Great improvements in solid loading were achieved by using the best large-to-small particle size ratio and large particle volume ratio found. The data and analysis could provide a new standard and solid experimental support for functional material printing

Performance-Optimized Components for Quantum Technologies via Additive Manufacturing

Novel quantum technologies and devices place unprecedented demands on the performance of experimental components, while their widespread deployment beyond the laboratory necessitates increased robustness and fast, affordable production. We show how the use of additive manufacturing , together with mathematical optimization techniques and innovative designs, allows the production of compact, lightweight components with greatly enhanced performance. We use such components to produce a magneto-optical trap that captures ∼ 2 × 10 8 rubidium atoms, employing for this purpose a compact and highly stable device for spectroscopy and optical power distribution, optimized neodymium magnet arrays for magnetic field generation and a lightweight, additively manufactured ultra-high vacuum chamber. We show how the use of additive manufacturing enables substantial weight reduction and stability enhancement, while also illustrating the transferability of our approach to experiments and devices across the quantum technology sector and beyond

Recent Advances and Future Trends in Nanophotonics

Nanophotonics has emerged as a multidisciplinary frontier of science and engineering. Due to its high potential to contribute to breakthroughs in many areas of technology, nanophotonics is capturing the interest of many researchers from different fields. This Special Issue of Applied Sciences on “Recent advances and future trends in nanophotonics” aims to give an overview on the latest developments in nanophotonics and its roles in different application domains. Topics of discussion include, but are not limited to, the exploration of new directions of nanophotonic science and technology that enable technological breakthroughs in high-impact areas mainly regarding diffraction elements, detection, imaging, spectroscopy, optical communications, and computing

Process–Structure–Properties in Polymer Additive Manufacturing II

Additive manufacturing (AM) methods have grown and evolved rapidly in recent years. AM for polymers is particularly exciting and has great potential in transformative and translational research in many fields, such as biomedicine, aerospace, and even electronics. The current methods for polymer AM include material extrusion, material jetting, vat polymerization, and powder bed fusion. In this Special Issue, state-of-the-art reviews and current research results, which focus on the process–structure–properties relationships in polymer additive manufacturing, are reported. These include, but are not limited to, assessing the effect of process parameters, post-processing, and characterization techniques