Colloidal Random Terpolymers: Controlling Reactivity Ratios of Colloidal Comonomers via Metal Tipping

We report on a versatile synthetic method of preparing colloidal copolymers and terpolymers composed of dipolar Au@Co core–shell nanoparticles (NPs) in the backbone, along with semiconductor CdSe@CdS nanorod (NR), or tetrapod (TP) side chain groups. A seven-step colloidal total synthesis enabled the synthesis of well-defined colloidal comonomers composed of a dipolar Au@CoNP attached to a single CdSe@CdS NR, or TP, where magnetic dipolar associations between Au@CoNP units promoted the formation of colloidal co- or terpolymers. The key step in this synthesis was the ability to photodeposit a single AuNP tip onto CdSe@CdS NR or TP that enables selective seeding of a dipolar CoNP onto the AuNP seed. We show that the variation of the AuNP size directly controlled the size and dipolar character of the CoNP tip, where the size modulation of the Au and Au@CoNP tips is analogous to control of comonomer reactivity ratios in classical copolymerization processes

Hybrids by Cluster Complex-Initiated Polymerization

Hybrids by Cluster Complex-Initiated Polymerizatio

Conformal Polymeric Multilayer Coatings on Sulfur Cathodes via the Layer-by-Layer Deposition for High Capacity Retention in Li–S Batteries

We report on the conformal coating of thickness-tunable multilayers directly onto the sulfur (S₈) cathodes by the layer-by-layer (LbL) deposition for the significant improvement in the performances of Li–S batteries even without key additives (LiNO₃) in the electrolyte. Poly­(ethylene oxide) (PEO)/poly­(acrylic acid) (PAA) multilayers on a single poly­(allylamine hydrochloride) (PAH)/PAA priming bilayer, deposited on the S₈ cathodes, effectively protected from the polysulfide leakage, while providing a Li⁺ ion diffusion channel. As a result, PAH/PAA/(PEO/PAA)₃ multilayer-coated cathodes exhibited the highest capacity retention (806 mAh g^–1) after 100 cycles at 0.5 C, as well as the high C-rate capability up to 2.0 C. Furthermore, the multilayer coating effectively mitigated the polysulfide shuttle effect in the absent of LiNO₃ additives in the electrolyte

Waveguide-Based Spectroelectrochemical Characterization of Band Edge Energies in Submonolayers of CdSe Quantum Dots Tethered to Indium–Tin Oxide Electrodes

We present here high sensitivity attenuated total reflectance (ATR) spectroelectrochemical studies of electron injection (reduction) into surface-tethered, submonolayer to monolayer coverages of CdSe quantum dots (QDs) linked to indium–tin oxide (ITO) electrodes using a strong X-type bifunctional phosphonic acid (PA) surface linker, octanediphosphonic acid (ODiPA). Estimates of conduction band energies (ECB) were obtained from the onset of absorbance bleaching as a function of QD diameter (3.2–6.4 nm) and as a function of the supporting electrolyte (LiClO4) concentration. For CdSe QDs created from combinations of moderately strong stearic acid, hexadecylamine, trioctylphosphine oxide, and trioctylphosphine ligands, surface-tethering was accompanied by decreases in QD diameter and loss of up to 25% volume for the largest QDs. For QDs prepared with PA ligands, followed by aggressive (3×) pyridine exchange to produce QDs with weak capping ligands, no size reduction was observed as a result of adsorption to the ODiPA/ITO surface. For both types of tethered CdSe QDs, significant stabilization of the reduction product of the surface-tethered QD was observed with ca. 700 meV lowering of ECB relative to estimates of ECB obtained from our recent in vacuuo UV-photoemission studies of bare CdSe QDs tethered to Au surfaces. A sizeable fraction of that stabilization is proposed to arise from the tethering of these asymmetric QDs to a complex, high dielectric constant interface region. At least 200 meV of the stabilization arises from concentration-dependent charge screening by the solution counter ion (Li+), with no evidence for the incorporation of Li+ as a result of the electron injection process. The overall stabilization in the reduced form of these tethered QDs is larger than seen for previous spectroelectrochemical studies of QD reduction, in solution, tethered at higher coverages to transparent electrodes, or as electrophoretically deposited multilayer QD thin films. This waveguide ATR spectroelectrochemical approach to estimating energetics for QDs tethered to semiconductor or oxide substrates at low surface coverages is likely to be relevant for a wide array of energy conversion and energy storage processes using nanomaterials and may be especially useful for studying the effects of surface coverage, type of surface linker, contacting solvent/electrolytes, and adsorbed molecular reactants

Band Edge Energetics of Heterostructured Nanorods: Photoemission Spectroscopy and Waveguide Spectroelectrochemistry of Au-Tipped CdSe Nanorod Monolayers

Conduction and valence band energies (<i>E</i>_CB, <i>E</i>_VB) for CdSe nanorods (NRs) functionalized with Au nanoparticle (NP) tips are reported here, referenced to the vacuum scale. We use (a) UV photoemission spectroscopy (UPS) to measure <i>E</i>_VB for NR films, utilizing advanced approaches to secondary electron background correction, satellite removal to enhance spectral contrast, and correction for shifts in local vacuum levels; and (b) waveguide-based spectroelectrochemistry to measure <i>E</i>_CB from onset potentials for electron injection into NR films tethered to ITO. For untipped CdSe NRs, both approaches show <i>E</i>_VB = 5.9–6.1 eV and <i>E</i>_CB = 4.1–4.3 eV. Addition of Au tips alters the NR band edge energies and introduces midgap states, in ways that are predicted to influence the efficiency of these nanomaterials as photoelectrocatalysts. UPS results show that Au tipping shifts <i>E</i>_VB closer to vacuum by up to 0.4 eV, shifts the apparent Fermi energy toward the middle of the band gap, and introduces additional states above <i>E</i>_VB. Spectroelectrochemical results confirm these trends: Au tipping shifts <i>E</i>_CB closer to vacuum, by 0.4–0.6 eV, and introduces midgap states below <i>E</i>_CB, which are assigned as metal–semiconductor interface (MSI) states. Characterization of these band edge energies and understanding the origins of MSI states is needed to design energy conversion systems with proper band alignment between the light absorbing NR, the NP catalyst, and solution electron donors and acceptors. The complementary characterization protocols presented here should be applicable to a wide variety of thin films of heterogeneous photoactive nanomaterials, aiding in the identification of the most promising material combinations for photoelectrochemical energy conversion

Universal Length Dependence of Rod-to-Seed Exciton Localization Efficiency in Type I and Quasi-Type II CdSe@CdS Nanorods

A critical step involved in many applications of one-dimensional seeded CdSe@CdS nanorods, such as luminescent solar concentrators, optical gains, and photocatalysis, is the localization of excitons from the light-harvesting CdS nanorod antenna into the light-emitting CdSe quantum dot seed. We report that the rod-to-seed exciton localization efficiency decreases with the rod length but is independent of band alignment between the CdSe seed and CdS rod. This universal dependence can be well modeled by the competition between exciton one-dimensional diffusion to the CdSe seed and trapping on the CdS rod. This finding provides a rational approach for optimizing these materials for their various device applications

Preparation of Dynamic Covalent Polymers via Inverse Vulcanization of Elemental Sulfur

The synthesis of dynamic covalent polymers with controllable amounts of sulfur–sulfur (S–S) bonds in the polymer backbone via inverse vulcanization of elemental sulfur (S₈) and 1,3-diisopropenylbenzene (DIB) is reported. An attractive feature of the inverse vulcanization process is the ability to control the number and dynamic nature of S–S bonds in poly­(sulfur-<i>random</i>-(1,3-diisopropenylbenzene)) (poly­(S-<i>r</i>-DIB) copolymers by simple variation of S₈/DIB feed ratios in the copolymerization. S–S bonds in poly­(S-<i>r</i>-DIB) copolymers of high sulfur content and sulfur rank were found to be more dynamic upon exposure to either heat, or mechanical stimuli. Interrogation of dynamic S–S bonds was conducted in the solid-state utilizing electron paramagnetic resonance spectroscopy and <i>in situ</i> rheological measurements. Time-dependent rheological property behavior demonstrated a compositional dependence of the healing behavior in the copolymers, with the highest sulfur (80 wt % sulfur) content affording the most rapid dynamic response and recovery of rheological properties

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-<i>random</i>-(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

Improving the Charge Conductance of Elemental Sulfur via Tandem Inverse Vulcanization and Electropolymerization

The synthesis of polymeric materials using elemental sulfur (S₈) as the chemical feedstock has recently been developed using a process termed inverse vulcanization. The preparation of chemically stable sulfur copolymers was previously prepared by the inverse vulcanization of S₈ and 1,3-diisopropenylbenzene (DIB); however, the development of synthetic methods to introduce new chemical functionality into this novel class of polymers remains an important challenge. In this report the introduction of polythiophene segments into poly­(sulfur-<i>random</i>-1,3-diisopropenylbenzene) is achieved by the inverse vulcanization of S₈ with a styrenic functional 3,4-propylenedioxythiophene (ProDOT-Sty) and DIB, followed by electropolymerization of ProDOT side chains. This methodology demonstrates for the first time a facile approach to introduce new functionality into sulfur and high sulfur content polymers, while specifically enhancing the charge conductivity of these intrinsically highly resistive materials

One Dimensional Photonic Crystals Using Ultrahigh Refractive Index Chalcogenide Hybrid Inorganic/Organic Polymers

We report on the fabrication of wholly polymeric one-dimensional (1-D) photonic crystals (i.e., Bragg reflectors, Bragg mirrors) via solution processing for use in the near (NIR) and the short wave (SWIR) infrared spectrum (1–2 μm) with very high reflectance (<i>R</i> ∼ 90–97%). Facile fabrication of these highly reflective films was enabled by direct access to solution processable, ultrahigh refractive index polymers, termed, Chalcogenide Hybrid Inorganic/Organic Polymers (CHIPs). The high refractive index (<i>n</i>) of CHIPs materials (<i>n</i> = 1.75–2.10) allowed for the production of narrow band IR Bragg reflectors with high refractive index contrast (Δ<i>n</i> ∼ 0.5) when fabricated with low <i>n</i> polymers, such as cellulose acetate (<i>n</i> = 1.47). This is the highest refractive index contrast (Δ<i>n</i> ∼ 0.5) demonstrated for an all-polymeric Bragg mirror which directly enabled high reflectivity from films with 22 layers or less. Facile access to modular, thin, highly reflective films from inexpensive CHIPs materials offers a new route to IR Bragg reflectors and other reflective coatings with potential applications for IR photonics, commercial sensing, and LIDAR applications