Li and 33 S solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy were used to identify the discharge products in lithium-sulfur (Li-S) battery cathodes. Cathodes were stopped at different potentials throughout battery discharge and measured ex-situ to obtain chemical shifts and T 2 relaxation times of the products formed. The chemical shifts in the spectra of both 6 Li and 33 S NMR demonstrate that long-chain, soluble lithium polysulfide species formed at the beginning of discharge are indistinguishable from each other (similar chemical shifts), while short-chain, insoluble polysulfide species that form at the end of discharge (presumably Li 2 S 2 and Li 2 S) have a different chemical shift, thus distinguishing them from the soluble long-chain products. T 2 relaxation measurements of discharged cathodes were also performed which resulted in two groupings of T 2 times that follow a trend and support the previous conclusions that long-chain polysulfide species are converted to shorter chain species during discharge. Through the complementary techniques of 1-D 6 Li and 33 S solid-state MAS NMR spectroscopy, solution 7 Li and 1 H NMR spectroscopy, and T 2 measurements, structural information about the discharge products of Li-S batteries is obtained.

A novel type of sol–gel derived zerogels that instantaneously swell greater than three times their dried volume in nonpolar solvents were investigated. Hybrid organic–inorganic materials that swell were only produced from a narrow set of precursors that possess an organic bridging group that contains an aromatic segment that is flexibly linked to the alkoxysilane polymerizable ends. Careful control over the processing conditions (catalyst, solvent, aging time) was necessary to yield animated zerogels. Various materials were studied by electron microscopy, infrared spectroscopy, nitrogen adsorption, and fluorescence spectroscopy using a covalently linked pyrene reporter. Collectively, the data support a model where swelling is derived from a morphology of interconnected organosilicate nanoparticles that are cross-linked to a particular extent during the gel state. Upon drying to the zerogel form, tensile forces generated by capillary-induced collapse of the polymeric matrix are released when interparticle interactions holding the dried material in the shrunken state are disrupted by a suitable solvent system. Swelling produced forces in excess of 50 N/g and is completely reversible. The molecular-scale organization of the nanoparticle structure seems critical for this swelling behavior. Further experiments indicate that the organosilicate materials can also swell in response to gas-phase organic molecules in a concentration dependent manner. These hybrid materials show promise for use in remediation technologies and chemical sensing.

No abstract

Polymer composites are of great interest in thermal conduction applications, while poor filler dispersion and enormous phonon scattering at composite interface become the critical bottleneck for efficient thermal conduction. This work presents a multiple hydrogen bonded supramolecular crystal, melamine-cyanurate (MC), with remarkable potential to develop self-assembled 2-D layered sheet structures while at the same time strengthening thermal interfaces. Such a composite is prepared by an in situ coprecipitation method resulting in homogeneous distribution of MC crystals. An extensive network of multiple hydrogen bonds present in this supramolecular assembly along with aligned layered structure facilitated efficient phonon transport. As a result, 65% enhancement of TC can be achieved by incorporating 2D MC crystals in the composites. The mechanism of MC crystal assembling and orientation in the composite are discussed as well. Overall this work offers a new strategy for the design and development of thermally conductive materials via supramolecular assembling.

The accurate distribution of countercations (Rb+ and Sr2+) around a rigid, spherical, 2.9‐nm size polyoxometalate cluster, {Mo132}42−, is determined by anomalous small‐angle X‐ray scattering. Both Rb+ and Sr2+ ions lead to shorter diffuse lengths for {Mo132} than prediction. Most Rb+ ions are closely associated with {Mo132} by staying near the skeleton of {Mo132} or in the Stern layer, whereas more Sr2+ ions loosely associate with {Mo132} in the diffuse layer. The stronger affinity of Rb+ ions towards {Mo132} than that of Sr2+ ions explains the anomalous lower critical coagulation concentration of {Mo132} with Rb+ compared to Sr2+. The anomalous behavior of {Mo132} can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion–cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion–{Mo132} interaction.

Imidazolium salts have shown great promise as anticancer materials. A new imidazolium salt (TPP1), with a triphenylphosphonium substituent, has been synthesized and evaluated for in vitro and in vivo cytotoxicity against bladder cancer. TPP1 was determined to have a GI 50 ranging from 200 to 250 μM over a period of 1 h and the ability to effectively inhibit bladder cancer. TPP1 induces apoptosis, and it appears to act as a direct mitochondrial toxin. TPP1 was applied intravesically to a bladder cancer mouse model based on the carcinogen N-butyl-N-(4hydroxybutyl)nitrosamine (BBN). Cancer selectivity of TPP1 was demonstrated, as BBN-induced tumors exhibited apoptosis but normal adjacent urothelium did not. These results suggest that TPP1 may be a promising intravesical agent for the treatment of bladder cancer.

A model system of styrene (St) and methyl methacrylate (MMA) was copolymerized in an NMR tube at 60 °C using 2,2′-azobis(isobutyronitrile) as the initiator and pyridazine as an internal standard to optimize an in situ 1 H NMR spectroscopic method for determining reactivity ratios by generating data at hundreds of instantaneous comonomer compositions (244 data points from 8 to 91 mol % St) starting with only nine initial comonomer compositions. The radical reactivity ratios of styrene (r St = 0.697 ± 0.010) and methyl methacrylate (r MMA = 0.491 ± 0.007) were determined by nonlinear least-squares fitting of a Mayo−Lewis plot of the instantaneous copolymer composition as a function of the comonomer feed composition using the terminal model and MINITAB statistical software, in which the copolymer composition was calculated by assuming that all comonomer consumed was converted to copolymer without side reactions; the results were similar to accepted literature values for the terminal and implicit penultimate models. After correcting for changes in the "lock" value at the initial stages of the copolymerization (because of solids formed in the sealed NMR tube), the same technique was used to determine the reactivity ratios of 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (FOSA; r FOSA = 1.624 ± 0.048) and 2-(N-ethylperfluorooctanesulfonamido)ethyl methacrylate (FOSM; r FOSM = 2.876 ± 0.083) in their radical copolymerizations with N,Ndimethylacrylamide (DMA; r DMA = 1.126 ± 0.031 with FOSA; r DMA = 0.859 ± 0.026 with FOSM).

No abstract