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

Coordination Assembly of Discoid Nanoparticles

Supramolecular chemistry utilizes coordination bonds to assemble molecular building blocks into a variety of sophisticated constructs. However, traditional coordination assemblies are based on organic compounds that have limited ability to transport charge. Herein, we describe coordination assembly of anisotropic FeS2 pyrite nanoparticles (NPs) that can facilitate charge transport. Zn2+ ions form supramolecular complexes with carboxylate end‐groups on NP surface, leading to multiparticle sheets with liquid‐crystal‐like organization. Conductivity and Hall carrier mobility of the p‐type layered semiconductor films with Zn2+ coordination bridging exceed those known for coordination compounds, some by several orders of magnitude. The nanoscale porosity of the assembled sheets combined with fast hole transport leads to high electrocatalytic activity of the NP films. The coordination assembly of NPs embraces the versatility of several types of building blocks and opens a new design space for self‐organized materials combining nanoscale and supramolecular structural motifs.Zinc ions are the “glue”: FeS2 nanoparticles (NPs) spontaneously assemble into sheets because of coordination bridging between Zn2+ and carboxylate groups on the NP surface. Conductivity and Hall carrier mobility of the p‐type semiconductor films exceed those known for coordination compounds and MOFs. The nanoscale porosity and fast hole transport of assembled sheets leads to high electrocatalytic activity of the NP films.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112281/1/8966_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/112281/2/anie_201502057_sm_miscellaneous_information.pd

Coordination Assembly of Discoid Nanoparticles

Supramolecular chemistry utilizes coordination bonds to assemble molecular building blocks into a variety of sophisticated constructs. However, traditional coordination assemblies are based on organic compounds that have limited ability to transport charge. Herein, we describe coordination assembly of anisotropic FeS2 pyrite nanoparticles (NPs) that can facilitate charge transport. Zn2+ ions form supramolecular complexes with carboxylate end‐groups on NP surface, leading to multiparticle sheets with liquid‐crystal‐like organization. Conductivity and Hall carrier mobility of the p‐type layered semiconductor films with Zn2+ coordination bridging exceed those known for coordination compounds, some by several orders of magnitude. The nanoscale porosity of the assembled sheets combined with fast hole transport leads to high electrocatalytic activity of the NP films. The coordination assembly of NPs embraces the versatility of several types of building blocks and opens a new design space for self‐organized materials combining nanoscale and supramolecular structural motifs.Schichtleiter: FeS2‐Nanopartikel (NPs) lagern sich durch koordinative Bindung zwischen Zn2+ und Carboxylatgruppen an der NP‐Oberfläche spontan zu Schichten zusammen. Die Leitfähigkeit und Hall‐Trägerbeweglichkeit der p‐Halbleiterfilme übertreffen die Werte bekannter Koordinationsverbindungen und MOFs. Die nanoskalige Porosität und der schnelle Lochtransport der Schichten führen zu einer hohen elektrokatalytischen Aktivität der NP‐Filme.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112255/1/9094_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/112255/2/ange_201502057_sm_miscellaneous_information.pd

Enzyme-assisted growth of nacreous CaCO3/polymer hybrid nanolaminates via the formation of mineral bridges

Laminated nanostructures in nacre have been adopted as models in the fabrication of strong, tough synthetic nanocomposites. However, the utilization of CaCO3 biominerals in these composites is limited by the complexity of the synthesis method for nanosized biominerals. In this study, we use the enzymatic reaction of urease to generate a nanoscale CaCO3 thin film to prepare CaCO3/polymer hybrid nanolaminates. Additional layers of CaCO3 thin film are consecutively grown over the base CaCO3 layer with the intercalation of organic layers. The morphology and crystallinity of the added CaCO3 layers depend strongly on the thickness of the organic layer coated on the underlying CaCO3 layer. When the organic layer is less than 20 nm thick, the amorphous CaCO3 layer is spontaneously transformed into crystalline calcite layer during the growth process. We also observe crystalline continuity between adjacent CaCO3 layers through interconnecting mineral bridges. The formation of these mineral bridges is crucial to the epitaxial growth of CaCO3 layers, similar to the formation of natural nacre. (C) 2016 Elsevier B.V. All rights reserved.N

Birefringence-Induced Modulation of Optical Activity in Chiral Plasmonic Helical Arrays

Chiral nanomaterials are characterized by handedness morphology on the nanoscale, manifested as preferential interaction with circularly polarized light. However, the origin of this light–matter interaction remains elusive. Here we simulated a model of chiral helical arrays of plasmonic nanoparticles with central anisotropic nanopillars to examine the effect of birefringence on the collective chiroptical response. Contrary to typical assumptions in previous works, we varied the biaxial refractive indices of the central nanopillars and observed a significant modulation of optical activity by calculating and characterizing circular dichroism (CD) spectra. The chiroptical response exhibited a sign change compared with that of the isotropic condition in a specific parametric range of negative birefringence. In addition, the CD peak increased by 3 to 16 as the ordinary refractive index increased from 1.5 to 3.0. These results are likely to be useful for designing chiral nanomaterials for applications in metamaterials, biosensors, and optoelectrical devices

Enhancement of fracture toughness in organic/inorganic hybrid nanolaminates with ultrathin adhesive layers

Nacre is composed of highly ordered organic/inorganic hybrid nanolaminated structures showing exceptional toughness. However, artificial fabrication of such nanoscale layered structures still remains a challenge in the area of nanocomposite films. In this study, we fabricated organic/inorganic hybrid nanolaminated films by using the layer-by-layer (LbL) deposition method, and obtained high fracture toughness by adjusting the interfacial interactions. Artificial composites with an inorganic content of 89.2 vol%-99.1 vol%, comparable to that of nacre, were fabricated via a bottom-up process with assist of the LbL method. In addition, the interfaces between organic/inorganic layers were discretely defined with the interfacial roughness of only 1.9 +/- 1.2 nm, as determined by high-resolution X-ray reflectivity (HR-XRR). More importantly, the insertion of adhesive layers that were only 8 angstrom-thick resulted in a significant increase (291-fold) in the fracture toughness at organic contents of 8-10 vol%. Therefore, tuning of the interfacial interaction has a significant effect on the release of fracture energy in hybrid laminated films. (C) 2016 Elsevier Ltd. All rights reserved.N

Layer-by-layer assembly for ultrathin energy-harvesting films: Piezoelectric and triboelectric nanocomposite films

Energy-harvesting devices such as piezoelectric and triboelectric nanogenerators (NGs), which can convert mechanical energy into electricity, are under development to be combined with various electronics. In particular, the rapid progress in microscale electronics such as nanorobotics or microelectromechanical devices has strongly increased the demand for ultrathin film devices. Therefore, the thickness, highly uniform structure, chemical composition, interfacial adhesion/interactions, and electrical performance of electrically active films should be carefully considered for high-performance ultrathin energy-harvesting devices. This review focuses on how layer-by-layer (LbL) assembly as a kind of thin film technology can be effectively applied to ultrathin piezoelectric and triboelectric films, and furthermore enhance device performance. First, we introduce the basics of various LbL assemblies using electrostatic, hydrogen-bonding, and covalent-bonding interactions. Then, the LbL-assembly-assisted piezoelectric and triboelectric NGs reported to date are reviewed. Finally, we briefly present perspectives on the direction of LbL assembly for the realization of various ultrathin piezoelectric and triboelectric NGs with high performance. © 2018 The Author(s)1

Effect of soft segment fraction on rate dependent damping of polyurethane and polyurethane-clay nanocomposites

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140415/1/6.2014-0799.pd