Jared J. Griebel

Colloidal Polymerization of Polymer- Coated Ferromagnetic Nanoparticles into Cobalt Oxide Nanowires

The preparation of polystyrene-coated cobalt oxide nanowires is reported via the colloidal polymerization of polymer-coated ferromagnetic cobalt nanoparticles (PS-CoNPs). Using a combination of dipolar nanoparticle assembly and a solution oxidation of preorganized metallic colloids, interconnected nanoparticles of cobalt oxide spanning micrometers in length were prepared. The colloidal polymerization of PS-CoNPs into cobalt oxide (CoO and Co(3)O(4)) nanowires was achieved by bubbling O(2) into PS-CoNP dispersions in 1,2-dichlorobenzene at 175 degrees C. Calcination of thin films of PS-coated cobalt oxide nanowires afforded Co(3)O(4) metal oxide materials. Transmission electron microscopy (TEM) revealed the formation of interconnected nanoparticles of cobalt oxide with hollow inclusions, arising from a combination of dipolar assembly of PS-CoNPs and the nanoscale Kirkendall effect in the oxidation reaction. Using a wide range of spectroscopic and electrochemical characterization techniques, we demonstrate that cobalt oxide nanowires prepared via this novel methodology were electroactive with potential applications as nanostructured electrodes for energy storage.

New Infrared Transmitting Material via Inverse Vulcanization of Elemental Sulfur to Prepare High Refractive Index Polymers

Polymers for IR imaging: The preparation of high refractive index polymers (n = 1.75 to 1.86) via the inverse vulcanization of elemental sulfur is reported. High quality imaging in the near (1.5 μm) and mid-IR (3-5 μm) regions using high refractive index polymeric lenses from these sulfur materials was demonstrated.

Synthesis of ferromagnetic cobalt nanoparticle tipped CdSe@CdS nanorods: critical role of Pt-activation

The synthesis of a ferromagnetic heterostructured material consisting of a CdSe@CdS nanorod attached to a single dipolar cobalt nanoparticle (CoNP) into a “matchstick” morphology is reported. CdSe@CdS nanorods were modified by an activation reaction with Pt(acac)2 which enabled selective one-sided deposition of a dipolar metallic CoNP-tip via the thermolysis of Co2(CO)8 in the presence of polystyrene ligands. Small (<2 nm) PtNP-tips on CdSe@CdS nanorods were found to be responsible for the selective deposition of CoNP-tips onto one terminus per nanorod. The influence of the Pt-activation step for cobalt tipping was investigated by examination of numerous conditions and characterization of intermediates and materials using transmission electron microscopy and synchrotron X-ray diffraction.

Analytical multimode scanning and transmission electron imaging and tomography of multiscale structural architectures of sulfur copolymer-based composite cathodes for next-generation high-energy density Li-S batteries

Poly[sulfur-random-(1,3-diisopropenylbenzene)] copolymers synthesized via inverse vulcanization represent an emerging class of electrochemically active polymers recently used in cathodes for Li-S batteries, capable of realizing enhanced capacity retention (1,005 mAh/g at 100 cycles) and lifetimes of over 500 cycles. The composite cathodes are organized in complex hierarchical three-dimensional (3D) architectures, which contain several components and are challenging to understand and characterize using any single technique. Here, multimode analytical scanning and transmission electron microscopies and energy-dispersive X-ray/electron energy-loss spectroscopies coupled with multivariate statistical analysis and tomography were applied to explore origins of the cathode-enhanced capacity retention. The surface topography, morphology, bonding, and compositions of the cathodes created by combining sulfur copolymers with varying 1,3-diisopropenylbenzene content and conductive carbons have been investigated at multiple scales in relation to the electrochemical performance and physico-mechanical stability. We demonstrate that replacing the elemental sulfur with organosulfur copolymers improves the compositional homogeneity and compatibility between carbons and sulfur-containing domains down to sub-5 nm length scales resulting in (a) intimate wetting of nanocarbons by the copolymers at interfaces; (b) the creation of 3D percolation networks of conductive pathways involving graphitic-like outer shells of aggregated carbons;

Multimodal Characterization of the Morphology and Functional Interfaces in Composite Electrodes for Li–S Batteries by Li Ion and Electron Beams

We report the characterization of multiscale 3D structural architectures of novel poly[sulfur-random-(1,3-diisopropenylbenzene)] copolymer-based cathodes for high-energy-density Li-S batteries capable of realizing discharge capacities >1000 mAh/g and long cycling lifetimes >500 cycles. Hierarchical morphologies and interfacial structures have been investigated by a combination of focused Li ion beam (LiFIB) and analytical electron microscopy in relation to the electrochemical performance and physicomechanical stability of the cathodes. Charge-free surface topography and composition-sensitive imaging of the electrodes was performed using recently introduced low-energy scanning LiFIB with Li+ probe sizes of a few tens of nanometers at 5 keV energy and 1 pA probe current. Furthermore, we demonstrate that LiFIB has the ability to inject a certain number of Li cations into the material with nanoscale precision, potentially enabling control of the state of discharge in the selected area. We show that chemical modification of the cathodes by replacing the elemental sulfur with organosulfur copolymers significantly improves its structural integrity and compositional homogeneity down to the sub-5-nm length scale, resulting in the creation of (a) robust functional interfaces and percolated conductive pathways involving graphitic-like outer shells of aggregated nanocarbons and (b) extended micro- and mesoscale porosities required for effective ion transport.

Multiscale Structural Architectures of Novel Sulfur Copolymer Composite Cathodes for High-Energy Density Li-S Batteries Studied by Analytical Multimode STEM Imaging and Tomography

Li-S rechargeable batteries are considered to be a promising light-weight, low-cost, and environmentally friendly candidate for next generation energy storage owing to high theoretical specific capacity of 1,672 mAh/g and high specific energy of 2,567 Wh/kg, which is 5 times that of current Li-ion technology. However, practical use of Li-S batteries remains limited because they suffer from gradual capacity fading caused by insulating properties of sulfur and polysulfide shuttle. Recently, poly(sulfur-random-(1,3diisopropenylbenzene) (poly(S-r-DIB)) copolymers have been introduced for their use as active materials in cathodes for Li-S batteries, and were found to be capable of realizing enhanced capacity retention (1005 mAh/g at 100 cycles) and a five-fold increase in lifetime (over 500 cycles) as compared to conventional sulfur-carbon cathodes [1, 2]. These materials are typically organized in a rough hierarchical 3D architecture which contains multiple components and is quite challenging to understand and characterize.

Sulfur copolymers for IR optics

Optical imaging and optical materials have developed hand-inhand since antiquity. Glass science has matured due to the demands placed by the disciplines of optics and astronomy, with a tremendous range of glass compositions developed over the past 300 years. More recently, advances in chemistry allowed amorphous polymers with low light scattering to emerge as an alternative to inorganic glasses because they are inexpensive and easily molded. Polymers are now widely used in visible imaging systems. However, the materials commonly used for these applications, such as polymethylmethacrylate and polycarbonate, are not transparent in the mid-wave IR (3–5 m) or the long-wave IR (8–12 m). Indeed, when IR imagers developed, new optical materials were needed. Over the past decade, the demand for compact, low-cost IR instruments has grown, in turn creating a demand for inexpensive optical materials that are transparent in several key IR spectral regions. Neither conventional oxide glasses nor hydrocarbon polymers can fill this need because their absorption increases significantly for wavelengths longer than 2–3 m. Crystalline IR materials such as silicon, germanium, zinc selenide, and halide salts are frequently used for IR optics, but are difficult to form into the complex shapes often needed for high-performance optics. Chalcogenide glasses1–3 have excellent transmission properties in the midto long-IR, but they incorporate either arsenic, sulfur, selenium, or tellurium. All except sulfur are toxic elements, and therefore difficult to fabricate safely. An IR-transmitting polymer could overcome many difficulties associated with the currently available materials. While considering how to create nontoxic polymers for use in this part of the spectrum, we must understand why materials absorb light. IR absorption is generally due to molecular vibrations. More specifically, when chemically bonded atoms vibrate, they absorb IR light related to their vibrational frequencies. By modeling bonds as mass-spring oscillators, we concluded that Figure 1. Transmission spectrum for a freestanding 200 m-thick polymer made from 80% sulfur and 20% 1,3-diisopropylbenzene (DIB) shows unusually high transmission for a polymer in most of the midIR. The inset shows the molecular structure for the polymer.