Stability and high energy densities are essential qualities for emerging battery electrodes. Because of its high specific capacity, silicon has been considered a promising anode candidate. However, the several-fold volume changes during lithiation and delithiation leads to fractures and continuous formation of an unstable solid-electrolyte interphase (SEI) layer, resulting in rapid capacity decay. Here, we present a carbon-silicon-carbon (C@Si@C) nanotube sandwich structure that addresses the mechanical and chemical stability issues commonly associated with Si anodes. The C@Si@C nanotube array exhibits a capacity of ∼2200 mAh g(-1) (∼750 mAh cm(-3)), which significantly exceeds that of a commercial graphite anode, and a nearly constant Coulombic efficiency of ∼98% over 60 cycles. In addition, the C@Si@C nanotube array gives much better capacity and structure stability compared to the Si nanotubes without carbon coatings, the ZnO@C@Si@C nanorods, a Si thin film on Ni foam, and C@Si and Si@C nanotubes. In situ SEM during cycling shows that the tubes expand both inward and outward upon lithiation, as well as elongate, and then revert back to their initial size and shape after delithiation, suggesting stability during volume changes. The mechanical modeling indicates the overall plastic strain in a nanotube is much less than in a nanorod, which may significantly reduce low-cycle fatigue. The sandwich-structured nanotube design is quite general, and may serve as a guide for many emerging anode and cathode systems.

All plants contain an unusual class of hemoglobins that display bis-histidyl coordination yet are able to bind exogenous ligands such as oxygen. Structurally homologous hexacoordinate hemoglobins (hxHbs) are also found in animals (neuroglobin and cytoglobin) and some cyanobacteria, where they are thought to play a role in free radical scavenging or ligand sensing. The plant hxHbs can be distinguished from the others because they are only weakly hexcacoordinate in the ferrous state, yet no structural mechanism for regulating hexacoordination has been articulated to account for this behavior. Plant hxHbs contain a conserved Phe at position B10 (Phe(B10)), which is near the reversibly coordinated distal His(E7). We have investigated the effects of Phe(B10) mutation on kinetic and equilibrium constants for hexacoordination and exogenous ligand binding in the ferrous and ferric oxidation states. Kinetic and equilibrium constants for hexacoordination and ligand binding along with CO-FTIR spectroscopy, midpoint reduction potentials, and the crystal structures of two key mutant proteins (F40W and F40L) reveal that Phe(B10) is an important regulatory element in hexacoordination. We show that Phe at this position is the only amino acid that facilitates stable oxygen binding to the ferrous Hb and the only one that promotes ligand binding in the ferric oxidation states. This work presents a structural mechanism for regulating reversible intramolecular coordination in plant hxHbs.

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Organic−inorganic nanocomposites consisting of electroactive conjugated polymer, poly(3-hexylthiophene) (P3HT), intimately tethered on the surface of semiconductor CdSe quantum dot (i.e., P3HT−CdSe nanocomposites) at the air/water interface formed via Langmuir isotherms were explored for the first time. The P3HT−CdSe nanocomposites displayed a high pressure plateau (∼10.5 mN/m) in the Langmuir isotherm, illustrating their complex packing at the air/water interface. The packing of the Langmuir−Blodgett (LB) depositions of nanocomposites was revealed by AFM measurements. Furthermore, photovoltaic devices fabricated from the LB depositions of the P3HT−CdSe nanocomposites exhibited a relatively high short circuit current, I SC, while maintaining a thin film profile. These studies provide insights into the fundamental behaviors of semiconductor organic−inorganic nanocomposites confined at the air/water interface as well as in the active layer of an organic-based photovoltaic device.

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This report describes the generation of three-dimensional (3D) crystalline silicon continuous network nanostructures by coupling all-organic block copolymer self-assembly−directed resin templates with low temperature silicon chemical vapor deposition and pulsed excimer laser annealing. Organic 3D mesoporous continuous network resin templates were synthesized from the all-organic self-assembly of an ABC triblock terpolymer and resorcinol-formaldehyde resols. Nanosecond pulsed excimer laser irradiation induced the transient melt transformation of amorphous silicon precursors backfilled in the organic template into complimentary 3D mesoporous crystalline silicon nanostructures with high pattern fidelity. Mechanistic studies on laser-induced crystalline silicon nanostructure formation revealed the resin template was carbonized during transient laser-induced heating in the milli-to nanosecond timescales, thereby imparting enhanced thermal and structural stability to support the silicon meltcrystallization process at temperatures above 1250 C. Photoablation of the resin material under pulsed excimer laser irradiation was mitigated by depositing an amorphous silicon overlayer on the resin template. This approach represents a potential pathway from organic block copolymer self-assembly to alternative functional hard materials with well-ordered 3D morphologies for potential hybrid photovoltaics, photonic, and energy storage applications.

Surface behavior of the pH-and thermoresponsive amphiphilic ABCBA pentablock copolymer has been studied with respect to the environmental conditions. We demonstrate that the pentablock copolymer poly((diethylaminoethyl methacrylate)-b-(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)-b-(diethylaminoethyl methacrylate)) possesses reversible temperature changes at the air-water interface in a narrow pH range of the water subphase. Significant diversity in the surface morphology of pentablock copolymer monolayers at different pH and temperatures observed were related to the corresponding reorganization of central and terminal blocks. Remarkable reversible variations of the surface pressure observed for the Langmuir monolayers at pH 7.4 in the course of heating and cooling between 27 and 50°C is associated with conformational transformations of terminal blocks crossing the phase line in the vicinity of the lower critical solution temperature point. The observed thermoresponsive surface behavior can be exploited for modeling of the corresponding behavior of pentablock copolymers adsorbed onto various biointerfaces for intracellular delivery for deeper understanding of stimuli-responsive transformations relevant to controlled drug and biomolecules release and retention. Surface behavior of the pH-and thermoresponsive amphiphilic ABCBA pentablock copolymer has been studied with respect to the environmental conditions. We demonstrate that the pentablock copolymer poly((diethylaminoethyl methacrylate)-b-(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)-b-(diethylaminoethyl methacrylate)) possesses reversible temperature changes at the air-water interface in a narrow pH range of the water subphase. Significant diversity in the surface morphology of pentablock copolymer monolayers at different pH and temperatures observed were related to the corresponding reorganization of central and terminal blocks. Remarkable reversible variations of the surface pressure observed for the Langmuir monolayers at pH 7.4 in the course of heating and cooling between 27 and 50°C is associated with conformational transformations of terminal blocks crossing the phase line in the vicinity of the lower critical solution temperature point. The observed thermoresponsive surface behavior can be exploited for modeling of the corresponding behavior of pentablock copolymers adsorbed onto various biointerfaces for intracellular delivery for deeper understanding of stimuli-responsive transformations relevant to controlled drug and biomolecules release and retention.

Hydrophobic trioctylphosphine oxide-functionalized CdSe quantum dots (CdSe-TOPO QDs) were transferred from organic solvent to aqueous solution via a simple yet novel biphasic ligand exchange process in one step, which involved the in-situ formation of hydrophilic dithiocarbamate moieties and subsequent ligand exchange with TOPO at the chloroform/water interface. The resulting water dispersible, dithiocarbamate functionalized CdSe QDs (i.e., D-CdSe) exhibited an increased photoluminescence (PL) quantum yield as compared to the original CdSe-TOPO QDs, suggesting an effective passivation of dithiocarbamate ligands on the QD surface. The D-CdSe QDs were then mixed with hydroxyl terminated TiO 2 nanoparticles. A decrease in the PL of the mixture was observed, indicating a possible charge transfer from the D-CdSe QDs to the TiO 2 nanoparticles. The reaction of the carboxyl group on the D-CdSe surface with the hydroxyl group on the TiO 2 rendered QDs in direct contact with TiO 2 , thereby facilitating the electronic interaction between them.