Altering Physical Properties of Particles with Surface Roughness - Anomalous Properties of 'Hedgehog' Particles.

Particles are ubiquitous and are integral components of modern technology. Sensitive to any alterations or even a small perturbation in its constitutive properties, sizes and shapes, particles have been utilized as a versatile means in a compact platform with which to manipulate, enhance or transform any physico-chemical properties in its environment. Amongst the variety, procedural and synthetic diversities and accompanying investigation of the physical and chemical properties of micron-scale particles having highly rough surfaces is barren in previous studies. Yet, most of the particles found in nature are “rough” particles. Therefore, a thorough survey that maps the deviation in properties from what is expected of standard predictions from analytically “smooth” particles, accompanied by systematic analysis protocols, is expected bring a broad impact to multiple scientific and practical disciplines. In the early phase of the research as a precursor to the construction of “rough” particles, the focus was on the synthesis of smooth polymeric microspheres. As microspheres had been extensively characterized, the focus was on the development and streamlining of large-scale fabrication process based on microfluidics setup. The second phase of the research involved the synthesis and characterization of “rough” particles having orthogonal orientation of high aspect ratio ZnO nanospikes on polymeric microspheres, which we called the ‘hedgehog’ particles to reflect its morphology. In this phase, we studied the ‘hedgehog’ particles in a colloidal system and report an anomalous colloidal dispersion behavior Lastly, owing to unique geometrical and material configurations, the ‘hedgehog’ particles enabled us to study electromagnetic response of “rough” particles, where all of its photonic compartments are dielectric and lie within the Mie scattering regime. Here, we showed that the presence of surface roughness alters the electromagnetic responses from what would have been expected of typical micron-scale dielectric particles. These studies are only a small subset of synthetic and property diversities possible with “rough” particle configurations. We believe that continued investigation and further expansion in the knowledge of “rough”, as well as particles of other configurations, may enable us a spectrum of design possibilities for realizing high performance substrates and devices.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135736/1/joonghb_1.pd

Self‐Assembly Mechanism of Spiky Magnetoplasmonic Supraparticles

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106774/1/adfm201302405.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/106774/2/adfm201302405-sup-0001-S1.pd

Mie resonance engineering in meta-shell supraparticles for nanoscale nonlinear optics

Supraparticles are coordinated assemblies of discrete nanoscale building blocks into complex and hierarchical colloidal superstructures. Holistic optical responses in such assemblies are not observed in an individual building block or in their bulk counterparts. Furthermore, subwavelength dimensions of the unit building blocks enable engraving optical metamaterials within the supraparticle, which thus far has been beyond the current pool of colloidal engineering. This can lead to effective optical features in a colloidal platform with unprecedented ability to tune the electromagnetic responses of these particles. Here, we introduce and demonstrate the nanophotonics of meta-shell supraparticle (MSP), an all dielectric colloidal superstructure having an optical nonlinear metamaterial shell conformed onto a spherical core. We show that the metamaterial shell facilitates engineering the Mie resonances in the MSP that enable significant enhancement of the second harmonic generation (SHG). We show several orders of magnitude enhancement of second-harmonic generation in an MSP compared to its building blocks. Furthermore, we show an absolute conversion efficiency as high as 10^-7 far from the damage threshold, setting a new benchmark for SHG with low-index colloids. The MSP provides pragmatic solutions for instantaneous wavelength conversions with colloidal platforms that are suitable for chemical and biological applications. Their engineerability and scalability promise a fertile ground for nonlinear nanophotonics in the colloidal platforms with structural and material diversity

Mie Resonance Engineering in Meta-Shell Supraparticles for Nanoscale Nonlinear Optics

Supraparticles are coordinated assemblies of discrete nanoscale building blocks into complex and hierarchical colloidal superstructures. Holistic optical responses in such assemblies are not observed in an individual building block or in their bulk counterparts. Furthermore, subwavelength dimensions of the unit building blocks enable engraving optical metamaterials within the supraparticle, which thus far has been beyond the current pool of colloidal engineering. This can lead to effective optical features in a colloidal platform with ability to tune the electromagnetic responses of these particles. Here, we introduce and demonstrate the nanophotonics of meta-shell supraparticle (MSP), an all dielectric colloidal superstructure having an optical nonlinear metamaterial shell conformed onto a spherical core. We show that the metamaterial shell facilitates engineering the Mie resonances in the MSP that enable significant enhancement of the second harmonic generation (SHG). We show several orders of magnitude enhancement of second-harmonic generation in an MSP compared to its building blocks. Furthermore, we show an absolute conversion efficiency as high as 10⁻⁷ far from the damage threshold, setting a benchmark for SHG with low-index colloids. The MSP provides pragmatic solutions for instantaneous wavelength conversions with colloidal platforms that are suitable for chemical and biological applications. Their engineerability and scalability promise a fertile ground for nonlinear nanophotonics in the colloidal platforms with structural and material diversity

Non-resonant Enhancement of Second-Harmonic Generation in a Dielectric Particle with a Nanostructured Nonlinear Metamaterial Shell

We demonstrate a new principle for realizing a miniaturized and scalable platform for nonlinear optics using dielectric particles with nanostructured nonlinear metamaterial shells. We show numerical and experimental results of enhanced second-harmonic generation in them

Branched Aramid Nanofibers

Interconnectivity of components in three‐dimensional networks (3DNs) is essential for stress transfer in hydrogels, aerogels, and composites. Entanglement of nanoscale components in the network relies on weak short‐range intermolecular interactions. The intrinsic stiffness and rod‐like geometry of nanoscale components limit the cohesive energy of the physical crosslinks in 3DN materials. Nature realizes networked gels differently using components with extensive branching. Branched aramid nanofibers (BANFs) mimicking polymeric components of biological gels were synthesized to produce 3DNs with high efficiency stress transfer. Individual BANFs are flexible, with the number of branches controlled by base strength in the hydrolysis process. The extensive connectivity of the BANFs allows them to form hydro‐ and aerogel monoliths with an order of magnitude less solid content than rod‐like nanocomponents. Branching of nanofibers also leads to improved mechanics of gels and nanocomposites.3D‐Gerüste mit effizienter Spannungsübertragung können mithilfe von verzweigten Aramid‐Nanofasern (BANFs) hergestellt werden. Die starke Verknüpfung der BANFs führt zu Hydrogel‐ und Aerogel‐Monolithen mit viel geringerem Feststoffgehalt als bei Verwendung stabförmiger Nanokomponenten. Die Verzweigung verbessert zudem die Gelmechanik, sodass kontinuierliche lumineszierende Mikrofasern und hochleistungsfähige Nanokomposite erhalten werden können.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138299/1/ange201703766-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138299/2/ange201703766_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138299/3/ange201703766.pd

Branched Aramid Nanofibers

Interconnectivity of components in three‐dimensional networks (3DNs) is essential for stress transfer in hydrogels, aerogels, and composites. Entanglement of nanoscale components in the network relies on weak short‐range intermolecular interactions. The intrinsic stiffness and rod‐like geometry of nanoscale components limit the cohesive energy of the physical crosslinks in 3DN materials. Nature realizes networked gels differently using components with extensive branching. Branched aramid nanofibers (BANFs) mimicking polymeric components of biological gels were synthesized to produce 3DNs with high efficiency stress transfer. Individual BANFs are flexible, with the number of branches controlled by base strength in the hydrolysis process. The extensive connectivity of the BANFs allows them to form hydro‐ and aerogel monoliths with an order of magnitude less solid content than rod‐like nanocomponents. Branching of nanofibers also leads to improved mechanics of gels and nanocomposites.Branching needed: The production of 3D networks with efficient stress transfer is enabled by branched aramid nanofibers (BANFs). The extensive connectivity of the BANFs leads to the formation of hydro‐ and aerogel monoliths with much less solid content than rod‐like nanocomponents. The branching also leads to improved gel mechanics, allowing the preparation of continuous microscale luminescent fibers and high‐performance nanocomposites.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138347/1/anie201703766.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138347/2/anie201703766-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138347/3/anie201703766_am.pd