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The thickness effect on the relaxation behavior and chain entanglements was investigated for thin polystyrene films. By following the time evolution of the wetting ridge at the surface induced by a...

Thermally sensitive polymers have attracted tremendous interest in the design of stimulus-responsive surfactants. In this article, poly(propylene oxide)-b-poly(N-isopropylacrylamide) (PPO-b-PNIPAm) with different block lengths of PNIPAm was synthesized through atom transfer radical polymerization (ATRP). Different from commercial Pluronic surfactants, four distinct sections appeared in the decrease of surface tension with concentration. First, with increasing concentration, the amount of adsorbed polymers increased and the surface tension decreased sharply until a plateau was reached, which was caused by the rearrangement of methyl groups. The increasing adsorbed amount of PPO-b-PNIPAm resulted in the rearrangement of isopropyl groups, which changed from a lying down or horizontal conformation to a standing up or vertical conformation. This behavior led to the decrease in surface tension in part III until the critical micelle concentration (CMC) was reached. The surface tension of PPO-b-PNIPAm was thermally responsive. Except for the hysteresis observed in the first cycle, the surface tension was reversible during the heating-and-cooling cycles. At low concentrations, the low surface tension at higher temperatures was mainly caused by the increasing adsorption amount and ordered arrangement of methyl groups, while the standing up conformation of isopropyl groups at higher concentrations resulted in the low surface tension observed at high temperatures.

The concept of free volume underpins the variations in polymer dynamics. Annihilation of free-volume holes through diffusion to surfaces has been proposed to determine the vitrification of the confined polymers. In this work, we assessed the hole diffusion dynamics in glassy thin poly (ethylene terephthalate) films with various thicknesses using a strategy based on covering the film surface with crystals of different sizes, which allows for changing the hole diffusion efficiency, thus tuning the glass transition temperature of the thin film (Tgfilm). The apparent activation energy for hole diffusion (Ea,hole) in the thin films was elucidated by modeling the correlation between Tgfilm and surface coverage of crystals using the free-volume hole diffusion model. Our results demonstrated a trend of linear decrease in Ea,hole with the increasing inverse film thickness (h–1), suggesting that the presence of a free surface with faster dynamics promotes hole diffusion in thin films. This finding demonstrates that the free volume release in thin films and thus the confined polymer dynamics can be modulated by changing the free surface properties of the films., B.Z. acknowledges financial support from Natural Science Foundation of China (Grant nos. 21973083) and Projects of International Cooperation and Exchanges NSFC (Grant nos. 22011530456). D.C. acknowledges financial support from the project PGC2018-094548-B-I00 (MICINN-Spain and FEDER-UE) and the project IT-1175-19 (Basque Government).

The film thickness and substrate interface are the two most common parameters to tune the dynamics of supported thin films. Here, we investigated the glass transition temperature (Tg) and thermal e...

The thickness dependent chain mobility in polymer films influenced by the interfacial effect was investigated by the cold crystallization behavior of thin poly(ethylene terephthalate) (PET) films c...

The thickness of the surface layer on both poly(methyl methacrylate) (PMMA) and polystyrene (PS) films was investigated by monitoring the surface reorganization of fluorinated tracer-labeled PMMA a...

One- and two-electron oxidation of a digallene stabilized by an N-heterocyclic carbene afforded the first stable gallium-based radical cation and dication salts, respectively. Structural analysis and theoretical calculations reveal that the oxidation occurs at the Ga=Ga double bond, leading to removal of π electrons of the double bond and a decrease of the bond order. The spin density of the radical cation mainly locates at the two gallium centers as demonstrated by EPR spectroscopy and theoretical calculations. Moreover, the reactivity of the radical cation salt toward nBu3 SnH and cyclo-S8 was studied; a digallium-hydride cation salt containing a Ga-Ga single bond and a gallium sulfide cluster bearing an unprecedented ladder-like Ga4 S4 core structure were obtained, respectively.

The one- and two-electron oxidation reactions of tetrathiolated di-tert-butylpyrene compound 1 with NO[Al(ORF)4] (ORF = OC(CF3)3) resulted in radical cation salt 1•+[Al(ORF)4]- and diradical dication salt 12+••·2[Al(ORF)4]-, respectively. Both salts were isolated as stable crystals and investigated by single-crystal X-ray diffraction, EPR spectroscopy, SQUID measurements, and UV-vis spectroscopy. The electron spin density is delocalized on one single sulfur-doped ring in 1•+ and on both sulfur-doped rings in 12+••. The diradical dication 12+•• features a robust triplet ground state, representing the first example of a high-spin sulfur-hydrocarbon diradical.

The lanthanide complexes [Cp*2Ln][N,N′-bpyB] (1: Ln = Dy; 3: Ln = Gd; Cp* = pentamethylcyclopentadienyl) and [222-cryptand-K][(Cp*2Ln)(N,N′-bpyB)] (2: Ln = Dy; 4: Ln = Gd) bearing the redox-noninno...

For the Co3O4/CaCO3 catalysts used for N2O decomposition, the activity of the catalyst prepared by stepwise precipitation is much superior to the catalysts prepared by impregnation or coprecipitation in the same composition. HRTEM observation and EDX analysis indicate that the stepwise precipitation leads to cobalt existing as little Co3O4 crystallites tightly bound to the CaCO3 particles. The special structure made the Co3O4 ideal accessibility and better interaction with the support in the catalyst, and the CaCo2.5(SP) catalyst with this structure is much more active than the CaCo2.5 catalyst reported in literature prepared in traditional method. At 300 °C, N2O in the feed gas 2000 ppmv N2O/Ar was completely converted over the CaCo2.5(SP) at 20,000 h−1. Moreover, the CaCo2.5(SP) catalyst exhibited better resistance to sintering at 800 °C and quite high activity under the presence of 5 vol% O2 and 2 vol% H2O at 350 °C as well.

Fe2O3 short nanorods, nanorods and nanowires were prepared by a facile hydrothermal method by using different flexible ligands (oxalic acid, succinic acid, adipic acid) as templates to adjust the L/D (length/diameter) ratios of the one-dimensional (1D) Fe2O3–nanostructures for the first time. The growth mechanism of Fe2O3 nanorods and nanowires were proposed. Their potential applications as anodes for lithium ion batteries were investigated by electrochemical analysis. This novel straightforward strategy to fabricate 1D metal oxide with different L/D ratios may provide a promising method to make advanced Fe2O3-based nanostructures for Li-ion battery applications.

In this article, interfacial π–π interactions of polystyrene (PS) chains next to aromatic-modified substrates were investigated. The results show that the glass transition temperature (Tg) and the modulus of the supported thin PS films increased gradually from phenyltrimethoxysilane-, naphthalenetrimethoxysilyl- to 9-anthracenyltrimethoxysilane-modified substrates with the increasing number of π electrons. For the p-tolyltrimethoxysilane (p-tolyl)-modified substrates, a very weak interfacial effect was observed. As revealed by sum frequency generation (SFG), the phenyl rings in the deuterated PS (dPS) side chains were perpendicular to the interface, which was induced by the anchored aromatic groups on the surface via the parallel-displaced configuration of the π–π interactions. Enhanced interfacial interactions with an increasing number of π electrons on the surface were revealed in which the peak area of the redshifted wavenumber of the ν2 C–D stretching vibration in dPS caused by π–π interactions increa...

Polymer–substrate interfaces are significant in determining the dynamics of nanoconfined polymers. In this study, an improved understanding of the interfacial effect was gained from the critical di...

The first main-group element radical based one-dimensional magnetic chain (1K)n was realized by one-electron reduction of the pyridinyl functionalized borane 1 with elemental potassium in THF in the absence of 18-crown-6 (18-c-6). The electron spin density of (1K)n mainly resides at the boron centers with a considerable contribution from central benzene and pyridine moieties. The spin centers exhibit an antiferromagnetic interaction as demonstrated by magnetic measurements and theoretical calculations. In contrast, the reduction in the presence of 18-c-6 afforded the separated radical anion salt 1K(Crown), in which the potassium cation was trapped by THF and 18-c-6 molecules. Further one-electron reduction of 1K(Crown) and (1K)n led to the diamagnetic monomer and polymer, respectively.

Degradable and thermosensitive microgels were successfully prepared via simultaneous quaternization and siloxane condensation during surfactant-free emulsion polymerization, with N-vinylcaprolactam as the main monomer and 1-vinylimidazole (VIM) as the comonomer, in the presence of (3-bromopropyl)trimethoxysilane (BPTMOS). The formation mechanism of cross-linking network was attributed to the hydrolysis and condensation of the methoxysilyl groups of BPTMOS and the quaternization of imidazole moiety of VIM by the bromine group of BPTMOS, leading to the microgels. The microgels were spherical in shape with a narrow size distribution, stable in an acidic buffer solution, but degradable in neutral and alkaline solutions. The presence of quaternized imidazolium in the same chain segment of Si-O-Si cross-linking points promoted the decomposition of Si-O-Si bonds and hence the degradation of the microgels. The obtained microgels could load and release the model drug, doxorubicin. The size, thermosensitivity, stability, degradation rate, and drug release behavior of the resultant microgels could be tuned by controlling the cross-linking degree, chemical composition, and degradation medium.

The surface average conformation of poly(ethylene terephthalate) (PET) films was modulated by adjusting the water content in corresponding trifluoroacetic acid (TFA) spin-coating solutions, which w...

Two bis(triarylamine) diradical dication salts 12+ 2[Al(ORF )4 ]- and 22+ 2[Al(ORF )4 ]- bridged with an orthogonal oriented bisanthrancene motif were synthesized. Their solid state and electronic structures were investigated by various experimental approaches in conjunction with theoretical calculations. Superconducting quantum interference device measurements and density functional theory calculations reveal that both of 12+ and 22+ feature open-shell singlet ground states with rather small singlet-triplet energy gaps; thus, they can be regarded as nearly pure diradicals (biradicals). Their diradical characters are enhanced by the orthogonal configuration of the bisanthrancene moiety which demonstrates the importance of the geometry of bridging units in turning the electronic structures of bis(triarylamine) dications.

Series of 0.5 wt.%Pt/NbnZrm catalysts (n: m = 0 ˜ 2) were investigated for catalyzing the selective catalytic reduction of NO by H2 (H2-SCR). It was found that matched capability of the catalyst activating H2 and that adsorbing NOx under the reaction conditions is much important for the H2-SCR catalyst. For 0.5 wt.%Pt/ZrO2, its relatively larger NOx adsorption capacity and lower capability of activating H2 made its catalytic activity much lower. Some Lewis acid sites were produced by modifying the ZrO2 with niobium oxide, which in turn properly decreased the NOx adsorption capacity and increased the capability of the resulted Pt/Nb1Zr1 catalyst for activating H2. The Pt/Nb1Zr1 catalyst exhibited much higher H2-SCR activity and N2 selectivity compared to Pt/ZrO2.

Series of Pt/HZSM-5 catalysts (x = 0.1–0.5) were prepared by impregnating H2PtCl6 or Pt(NO3)2 on HZSM-5 and characterized by FTIR and XPS. It was found that Pt is predominantly located on the zeolite outside surface for the catalysts prepared from H2PtCl6, whereas large portion of Pt existed in the zeolite channels for the catalysts prepared from Pt(NO3)2. In the H2-SCR, the Pt on the zeolite outside surface plays the role of activating H2, while that in the zeolite channels merely adsorbs NOx species for the reaction. For the catalysts, proper NOx adsorption capacity matching the property activating H2 is indispensable for increasing the H2 efficiency and the N2 selectivity. Some cations such as Al3+ capable of accepting more NOx species in the zeolite channels effectively improved the catalytic performance.

Block copolymers confined in nanopores provide unique achiral systems for the formation of helical structures. With AB diblock copolymers, stable single and double helical structures are observed. Aiming to obtain more different helical structures, we replace the AB diblock copolymer with linear ABC triblock copolymers. We speculate that a core-shell superstructure is formed within the nanopore, which is composed of a C-core cylinder wrapped by B-helices within the A-shell. Accordingly, the pore surface is set to be most attractive to the majority A-block and a typical set of interaction parameters is chosen as χACN ≪ χABN = χBCN = 80 to generate the frustrated interfaces. Furthermore, the volume fraction of B-block is fixed as fB = 0.1 to form helical cylinders. A number of helical structures with strands ranging from 1 to 5 are predicted by self-consistent field theory, and in general, the number of strands decreases as the volume fraction of C-block fC increases in a given nanopore. More surprisingly, the variation of helical strand in the confined system has an opposite trend to that in the bulk, which mainly results from the constraint of the cylindrical confinement on the change of the curvature between the outer A-layer and the inner B/C-superdomain. Our work demonstrates a facile way to fabricate different helical superstructures.

Core-shell type Co0.24Ba (CS) catalyst was prepared by adsorption-deposition method, in which cobalt oxide with small amount of Ba incorporation mainly exists in the porous shell over the BaCO3 support core. This structure of the catalyst not only endues the active component Co a high accessibility to the reactant, but also made the active component promoted by barium better. Due the special structure, the catalyst is much more active in N2O decomposition compared with the catalysts with traditional structure. Over the Co0.24Ba (CS) catalyst that containing only 8.91 wt.% of Co3O4, N2O in feed gas 2000 ppmv N2O/Ar with 20,000 h-1 was 100% decomposed at 400 °C.

Glassy polymer films with extreme stability could enable major advancements in a range of fields that require the use of polymers in confined environments. Yet, from a materials design perspective, we now know that the glass transition temperature (Tg) and thermal expansion of polymer thin films can be dramatically different from those characteristics of the bulk, i.e., exhibiting confinement-induced diminished thermal stability. Here, we demonstrate that polymer brushes with an ultrahigh grafting density, i.e., an ultradense brush morphology, exhibit a significant enhancement in thermal stability, as manifested by an exceptionally high Tg and low expansivity. For instance, a 5 nm thick polystyrene brush film exhibits an ∼75 K increase in Tg and ∼90% reduction in expansivity compared to a spin-cast film of similar thickness. Our results establish how morphology can overcome confinement and interfacial effects in controlling thin-film material properties and how this can be achieved by the dense packing and molecular ordering in the amorphous state of ultradense brushes prepared by surface-initiated atom transfer radical polymerization in combination with a self-assembled monolayer of initiators.

Triplet diradicals have attracted tremendous attention due to their promising application in organic spintronics, organic magnets and spin filters. However, very few examples of triplet diradicals with singlet–triplet energy gaps (ΔEST) over 0.59 kcal mol−1 (298 K) have been reported to date. In this work, we first proved that the dianion of 2,7-di-tert-butyl-pyrene-4,5,9,10-tetraone (2,7-tBu2-PTO) was a triplet ground state diradical in the magnesium complex 1 with a singlet–triplet energy gap ΔEST = 0.94 kcal mol−1 (473 K). This is a rare example of stable diradicals with singlet–triplet energy gaps exceeding the thermal energy at room temperature (298 K). Moreover, the iron analog 2 containing the 2,7-tBu2-PTO diradical dianion was isolated, which was the first single-molecule magnet bridged by a diradical dianion. When 2 was doubly reduced to the dianion salt 2K2, single-molecule magnetism was switched off, highlighting the importance of diradicals in single-molecule magnetism., We report a triplet diradical dianion in magnesium complex with ΔEST = 0.94 kcal mol−1 (473 K). Its iron analog is the first single-molecule magnet bridged by a diradical dianion, and the SMM property is switched off through two-electron reduction.

It has been demonstrated that tailoring the properties of semiconductor/dielectric interfaces with fluorinated polymers yields better performance for organic field-effect transistors (OFETs). However, it remains a challenge to fabricate bottom-gate OFET devices on fluorinated dielectrics using solution-processed methods due to the poor wettability of fluorinated dielectrics. Here, we utilized the diffusion of fluorinated poly(methyl methacrylate) (PMMA) to construct the fluorine-rich semiconductor/dielectric interface to achieve the fabrication of bottom-gate OFETs with a solution-processed poly(3-hexylthiophene) (P3HT) semiconductor layer. The consequences indicate that the fluorinated dielectrics can effectively decrease the charge traps density at the semiconductor/dielectric interface and promote the edge-on orientation of P3HT on the dielectric surface. Thus, the devices based on fluorinated PMMA modified dielectrics exhibit higher carrier mobility and electrical stability than those of the fluorine-free devices. Our investigation affords a new strategy for the design and interface optimization of devices, which may further advance the performance of OFET devices.

Low energy density is the major obstacle for the practical all-solid-state supercapacitors, which may be raised by the combination of the pseudocapacitance with the electrochemical double-layer capacitance. Although graphene and polyaniline have been demonstrated two effective materials, the synthetic route of graphene and their hybrid mode largely dictated the capacitive performances and cyclability of graphene/polyaniline nanocomposites. Herein, we employed commercial graphite fluoride as the precursor to obtain graphene with a well-preserved carbon lattice. After graphite fluoride functionalization by p-phenylenediamine (pPDA) and in situ oxidative polymerization of anilines, polyaniline (PANI) chains were covalently attached to graphene framework through pPDA bridges. Multiple characterizations were performed to confirm the covalent binding mode between graphene scaffolds and PANI partners, and electrochemical tests unraveled the as-prepared G–pPDA–PANI triads delivered a gravimetric capacitance as high as 638F g−1 and a further amplified volumetric capacitance (up to 759F cm−3). The bendable all-solid-state supercapacitors yielded an encouraging energy density of over 18 W h L−1 at a power density high to 5,950 W L−1, while exhibiting an exceptional rate capability, cycling stability and mechanical flexibility.

The concept of odd-electron σ–bond was first proposed by Linus Pauling. Species containing such a bond have been recognized as important intermediates encountered in many fields. A number of radicals with a one-electron or three-electron σ-bond have been isolated, however, no example of a diradical based odd-electron σ-bonds has been reported. So far all stable diradicals are based on two s/p-localized or π-delocalized unpaired electrons (radicals). Here, we report a dication diradical that is based on two Se∴Se three-electron σ–bonds. In contrast, the dication of sulfur analogue does not display diradical character but exhibits a closed-shell singlet., Stable diradicals are generally based on two s/p-localized or π-delocalized unpaired electrons (radicals). Here, the authors report a dication diradical that is based on two Se∴Se three-electron σ-bonds.

Graphene-based membranes have been extensively explored owing to their excellent separation properties. In this paper, multiple factors regarding desalination performance were investigated by molecular dynamics (MD) simulations. These factors include the interlayer spacing distance (H), the gap width (dG), offset (O), and the number of gaps and layers in a multilayer graphene membrane (MGM). It is found that salt rejection is influenced significantly by the interlayer spacing distance owing to the largest free energy between ions and graphene sheets as well as the relatively larger size of the hydration layer around the ions. The optimal desalting parameter (dG = 1 nm, H = 0.8 nm) was selected; MGM systems based on the optimized parameter exhibited excellent salt rejection for NaCl, MgCl2 and CaCl2 solutions. These results can provide some ideas for the future design of graphene-based membranes.

Radical pimers are the simplest and most important models for studying charge-transfer processes and provide deep insight into π-stacked organic materials. Notably, radical pimer systems with magnetic bi- or multistability may have important applications in switchable materials, thermal sensors, and information-storage media. However, no such systems have been reported. Herein, we describe a new pimer consisting of neutral N-(n-propyl) benzene triimide ([BTI-3C]) and its anionic radical ([BTI-3C]-. ) that exhibits rare magnetic multistability. The crystalline pimer was readily synthesized by reduction of BTI-3C with cobaltocene (CoCp2 ). The transition occurred with a thermal hysteresis loop that was 27 K wide in the range of 170-220 K, accompanied by a smaller loop with a width of 25 K at 220-242 K. The magnetic multistability was attributed to slippage of the π-stacked BTI structures and entropy-driven conformational isomerization of the side propyl chains in the crystalline state during temperature variation.

We demonstrated, using grazing incidence wide-angle X-ray diffraction (GI-WAXD), sum frequency generational spectroscopy (SFG), and atomic force microscopy (AFM), that the aggregation state and mol...

The binder-free films of hollow Na2Ti3O7 (NTO) spheres and reduced graphene oxide were employed as anodes for sodium ion batteries. The films were assembled by vacuum filtration of the pre-prepared hollow NTO spheres and reduced graphene oxide nanosheets (NTO-rGO). The ultrathin nanosheets, as the building blocks of hollow spheres, optimize the sodium ion transportation at the particle level. Furthermore, the hollow spheres were employed to prevent the restacking of reduced graphene oxide nanosheets and optimize the sodium ion transportation at electrode level. Thanks to the optimized ion transportation on both particle and electrode levels, the as-prepared NTO-rGO film showed enhanced rate performance of a high capacity of 135 mA h g−1 under the current density of 500 mA g−1 and over 650 cycles, demonstrating the superiority of this unique structure.

Microgels with a thermo-sensitive poly(N-isopropylacrylamide) (polyNIPAm) backbone and bis-imidazolium (VIM) ionic cross-links, denoted as poly(NIPAm-co-VIM), were successfully prepared. The as-synthesized ionic microgels were converted to nanoreactors, denoted as Au@PNI MGs, upon generation and immobilization of gold nanoparticles (Au NPs) of 5–8 nm in size into poly(NIPAm-co-VIM). The content of Au NPs in microgels could be regulated by controlling the 1,6-dibromohexane/vinylimidazole molar ratio in the quaternization reaction. The microgel-based nanoreactors were morphologically spherical and uniform in size, and presented reversible thermo-sensitive behavior with volume phase transition temperatures (VPTTs) at 39–40 °C. The Au@PNI MGs were used for the reduction of 4-nitrophenol, of which the catalytic activity could be modulated by temperature.

Fe3O4@C supported ultrasmall and highly monodisperse ruthenium (Ru) nanoparticles (Ru/Fe3O4@C) were prepared as novel nanocatalysts for hydrogenation reactions. The catalysts displayed high activity for the hydrogenation of rosin to form hydrogenated rosin with extraordinary selectivity. The role of controlled carbon size on the catalytic properties of the catalysts was studied. The Ru/Fe3O4@C catalyst can be easily separated from the organic solvent by applying an external magnetic field and the separated Ru/Fe3O4@C can simply and efficiently used in ten consecutive runs without significant decrease in activity. Significantly, Ru/Fe3O4@C nanocatalysts showed a wide substrate scope for hydrogenation reactions under mild conditions.

A family of aromatic acids containing different binding sites, including 5-chloro-2-hydroxybenzoic acid, 2,3-dihydroxybenzoic acid, salicylic acid, 3-nitrophthalic acid, 4,5-dichlorophthalic acid, 6-hydroxy-2-naphthoic acid and tetrafluorophthalic acid, were allowed to react with 2,3-dimethylpyrazine to assemble single molecule into diverse structures. Seven cocrystals were successfully synthesized and characterized by single crystal X-ray diffraction. Crystal structure analysis shows that O H⋯N H-bonds are involved in the formation of all 1D chains of the seven cocrystals. Moreover, C H⋯O H-bonds play a crucial role in the 3D supramolecular network. In the crystal structures of cocrystals 1, 2 and 4, noncovalent interaction π-π stacking can be considered as a significant influencing factor. In 2, the self-assembly of 3D tessellate-type supramolecular architecture in solution is driven mainly by π-π interactions, to a lesser extent, and by weak hydrogen bond. In 3, two carboxylic acid molecules link each other to form dimers [synthon V R22 (12)] but in 7 carboxylic acid molecules and water molecules are connected to afford tetramer [synthon XVII R44 (12)], further generating zig-zag chains via O H⋯N intermolecular H-bonds. What is worth mentioning, acid and alkali molecules constitute tape chains through the way of forming synthons VII R22 (14) and VIII R66 (30), XI R44 (24) and XII R22 (10) in crystals 4 and 5, respectively. The strong orthogonally directed C H···π interactions lie in the 2D architecture of 6. Meanwhile, solvent molecules make a significant part in preparation of supramolecular structures in 6 and 7. Results show that solvent molecules serve as H-bond donors/acceptors to complete the various motif.

Antimony sulfoiodide (SbSI) is commonly known as a prototypical ferroelectric semiconductor. We report herein a top-down strategy of ball-milling followed by size selective centrifugation to prepare SbSI nanocrystals (NCs). Taking the well dispersed SbSI NCs of the average size of 80 nm as photocatalyst, a record high visible light efficiency in photodegradation of methyl orange (MO) in water was achieved. By using a 300 W xenon lamp with a 420 nm cutoff filter and with the SbSI NCs of 1 g/L, the MO solution of 30 mg/L can be degraded ∼99% in 10 s. The pseudo-first-order rate constant (k) of the photodegradation is k = 0.42 s–1. For high concentrated MO of 150 mg/L, it can be ∼99% degraded in 30 s at an elevated temperature of 65 °C (k = 0.15 s–1). With further increase of the SbSI NCs concentration to 4 g/L, the 150 mg/L MO can be ∼99% degraded in 1 min at room temperature (k = 0.095 s–1). The small size of the SbSI NCs and efficient generation of singlet oxygen were found to be the key factors for the o...

The local conformation of polystyrene (PS) and deuterated PS at the interface with quartz substrates, which were covered with phenyl groups using phenyltrimethoxysilane (PTS) under various conditions, was examined by sum frequency generation spectroscopy. As evidenced by the red-shift of the wavenumber of the v2 vibration mode for phenyl groups, it was claimed that PTS phenyl groups standing vertically from the quartz surface induced the perpendicular orientation of PS phenyl rings by energetically favorable parallel-displaced π–π interactions at the interface. The local conformation of PS chains strongly anchored onto the substrate by the π–π interactions remained almost unchanged for 48 h even at a temperature 60 K higher than the bulk glass transition temperature. That is, the interfacial π–π interactions facilitated the adsorption of PS chains on the substrate to attain a large enthalpic gain, resulting in significantly slower dynamics of PS chains at the interface. Our results illustrate the importan...

Two salts (2 and 4) containing the radical cations of complexed diphosphenes have been isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy, IR spectroscopy, and single-crystal X-ray diffraction. The P-P bond is coordinated to the Cr center either in an end-on (in 2) or a side-on (in 4) fashion. The spin density of the radical is delocalized over the Cr atom and the two P atoms in 2 whereas the unpaired electron is mainly localized on the Cr atom in 4. This work provides the first example of a complexed diphosphene radical (2) featuring novel three-center three-electron (3c-3e) π-bonding in the Cr-P-P unit, and the first example of a 17 e Cr radical with a side-on π-bonded ligand (4).

One-dimensional (1D) spin-1 (S = 1) chain of organic radicals with low local magnetic anisotropy may provide a better understanding of the low-dimensional magnetism. We report solid-state studies, including single crystal X-ray crystallography, of air-stable tetraazacyclophane diradical dication salt 12·2+·2[Al(OC(CF3)2CH3)4]− with a triplet ground state (ΔEST ≈ 0.5 kcal mol–1). The magnetic behavior for 12·2+ at low temperature is best modeled by 1D spin S = 1 Heisenberg chain with intrachain antiferromagnetic coupling of J′/k = −5.4 K, which is associated with the interaryl C···C contacts, including π–π interactions. Zero-field splitting value, |D/hc| ≈ 5.6 × 10–3 cm–1, for 12·2+ is rather small; thus, the 1D chains are characterized by the high degree of isotropicity |D/2J′| ≈ 7.5 × 10–4. The diradical dication salt possesses extraordinary stability with onset of decomposition at temperature of about 180 °C (∼450 K), based on thermogravimetric analysis and EPR spectroscopy.

Chemometric analysis was used to classify different oils based on the m/z 256 mass chromatogram. Three hundred oil samples comprised of 12 LFOs, 104 HFOs (13 weathered fuel oils), and 184 crude oil samples (63 weathered crude oils) were analyzed by GC–MS, and the m/z 256 mass chromatogram was chosen for classification. After normalization, the m/z 256 mass chromatograms were aligned using the correlation optimized warping (COW) method with segment lengths of 50 data points and slack parameters of 4 data points. They were then analyzed by principal component analysis (PCA). The score graphs of the PCs revealed that there was a good discriminant for HFOs, LHOs and oils. According to the changing tendency of the correct sample percentage, five PCs were chosen for the linear discriminant analysis (LDA). A good model with three discriminant equations for HFOs, LFOs and oils was obtained. For the training set with 172 samples, the correct percentage reached 100%, and 99% was obtained for the test set with 128 samples. This study proved that the COW-PCA-LDA method based on the m/z 256 mass chromatogram can be used in oil fingerprinting identification, especially for oil type classification.

Water transport across nanoscale channel is of great interest in biology, geology, and materials science. The boron nitride nanotubes (BNNTs) with different charge distributions were employed as a model to investigate the water transport in nanoscale channel through molecular dynamics simulations. It is found that the transport of water could influenced by the charge regulation in the terminal of BNNTs. If the diameter of BNNTs is small, the water permeation in charge-tunable BNNT(6,6) are mainly determined by transportation dynamics of water molecules located around the entrance and exit due to trap phenomenon. The trap phenomenon would be weaken with the increase of BNNTs' diameter, and the dynamics of water transportation through the BNNTs would be speeded up owing to the enhanced effect caused by the directional electric field and the relatively larger pore channel.

Ultrathin polymer films exhibit a liquidlike mobile surface layer near the free surface, which plays an important role in the size-dependent physical properties of polymer nanomaterials. Most research has focused on the thickness of the surface layer related to segmental relaxation, while few studies have focused on that related to large-scale segmental rearrangement, such as crystallization and diffusion. In this paper, a simple measurement of the surface mobile layer thickness with accelerated crystallization kinetics in a poly(ethylene terephthalate) film was performed by examining the stepwise crystallization behavior. The thickness of the surface crystallization layer (hscry) was determined by ellipsometry or X-ray reflection and was taken as the surface mobile layer thickness. hscry was observed to increase from 4 to 13 nm when the temperature increased from 343 to 373 K without any dependence on the molecular weight or film thickness, which fits well with the theoretical prediction by the cooperati...

A diradical dication of a 4,4'-di(bis(1,4-methylphenyl)amino)-p-terphenyl oligomer has been characterized in solid-state by Raman spectroscopy and thermo-spectroscopy together with quantum chemical calculations. The diradical character has been evaluated on the basis of the Raman spectra and as a function of temperature. A complete understanding of the nature of the changes in solid state has been provided based on a pseudo-Jahn-Teller effect, which is feasible owing to the fine balance between quinoidal/aromatic extension among consecutive rings and steric crowding. This study contributes to the further comprehension of the molecular and electronic structures of these particular diradical molecules with strong implications on the understanding of the nature of chemical bonds in the limits of high electronic correlation or π-conjugation.

To investigate protein-resistant surfaces with heterogeneous nanopatterns, V-shaped polymer brushes composed of a hydrophilic methoxypoly(ethylene glycol) (mPEG) arm and a hydrophobic polystyrene (PS) or fluorinated poly(methyl methacrylate) (PMMA-b-PFMA) arm were prepared, in which the surface structure and phase-separation behavior were controlled by altering the relative lengths of the two arms. The protein resistance of these amphiphilic brushes was better than that of pure poly(ethylene glycol) (PEG) brushes, and when the domain size of the phase-separated structures was about twice the size of the protein molecules, the surfaces exhibited optimal protein repellence. At the same time, the amount of protein adsorption was well related to both the adhesion and the relative friction coefficient of the protein on the brush surface. A heterogeneous surface with phase-separated domains twice the size of protein molecules may be beneficial for minimizing protein adsorption through the synergistic effect of ...

Two‐electron oxidations of three 1,2‐di(bisphenylamino)‐benzenes afforded a class of nitrogen analogues of o ‐quinodimethane, one of which features unexpected non‐Kekule diradical character, sharply different from o ‐quinodimethane.

The local conformation of poly(styrene-co-butadiene) rubber (SBR) chains in direct contact with a quartz substrate was examined by interface-sensitive sum-frequency generation (SFG) spectroscopy. SFG signals, which could be obtained from functional groups only oriented at the interface, were clearly observed for SBR in a film at room temperature which was much higher than the bulk glass transition temperature (Tg). When the film was thermally annealed, SBR chains at the quartz interface changed their conformation to one with a lower energy state, accompanied by the randomization of both the main and side chain parts. The characteristic temperature, at which interfacial chains started to lose their orientations, was much higher than the bulk Tg. Also, the extent found to be more remarkable for the spin-coated film than for the solvent-cast one. This implies that the stress accumulated at the interface, which resulted from the centrifugal force during the spin-coating process, accelerates the mobility of ch...

Thin polymer films with well-assembled fluorinated groups on their surfaces are not easily achieved via spin-coating film-fabrication methods because the solution solidifies very rapidly during spin-coating, which hinders the fluorinated moieties from segregating and organizing on the film surface. In this contribution, we have proposed a comprehensive strategy toward achieving well-ordered fluorinated thin films surfaces by optimizing the molecular organization at air/liquid interface of the film-formation solutions. To validate such a route, poly(methyl methacrylate) (PMMA) end-capped with several 2-perfluorooctylethyl methacrylate (FMA) units was employed as the model polymer for investigations. The air/solution interfacial structures were optimized by systematically changing the polymer chain structures and properties of the casting solvents. It was found that the polymers that form loosely associated aggregates (e.g., FMA1- ec-PMMA65- ec-FMA1) and a solvent with better solubility to FMA while having not too low surface tension (i.e., toluene) can combine to produce solutions with well-assembled FMA at the interfaces. By spin-coating the solutions with well-organized interfaces, an ultrathin film with perfluorinated groups that were highly oriented toward the film surface was readily achieved, exhibiting surface energies as low as 7.2 mJ/m2, which is among the lowest reported so far for the spin-coated thin films, and a very high F/C ratio (i.e., 0.98).

Apparent activation energies and reaction rates of N2O decomposition via L-H and E-R routes over Co3O4 were experimentally estimated after considering the increase of active sites with reaction temperature. It was found that the apparent activation energy is 32.9 kJ/mol for the L-H route and 44.8 kJ/mol for the E-R route, while the order of reaction with respect to O2 is − 0.367 at 350 °C and − 0.338 at 450 °C. The contribution of the E-R route to the total reaction rate was found to be considerably increased with the reaction temperature and which was well interpreted by the apparent activation energies of the two reaction routes.

One-electron reductions of Mes*As=Fl* (1; Fl*=2,7-di-tert-butylfluorenylidene, Mes*=2,4,6-tBu3 C6 H2 ) and diarsaalkenes [1,2-b]-IF(=AsMes*)2 (2; IF=indenofluorene) with potassium led to the isolation of the arsenic-centered radical anion salts 1K and 2K, respectively. The diradical dianion salts 2K2 and 3K2 were afforded by the reduction of 2 and 2,8-tBu2 -[2,1-b]-IF(=AsMes*)2 (3) with an excess amount of KC8 . The radicals have been investigated by single-crystal X-ray crystallography, EPR, and UV/Vis absorption spectroscopy, along with theoretical calculations. The calculations revealed that 2K2 and 3K2 feature open-shell singlet ground states with singlet-triplet energy gaps of 2.1 and 1.0 kcal mol-1 , respectively. They are readily thermally excited to triplet states as demonstrated by EPR spectroscopy. The obtained diradicals represent the first examples of heavier Group 15 element centered diradicals with experimentally observable triplet states.

Series of AgxCo (x = 0 ∼ 0.08) oxide catalysts prepared by coprecipitation (CP) was investigated in the N2O decomposition. The addition of Ag into cobalt oxide significantly enhanced the activity of the catalyst by both greatly decreasing the average size of the Co3O4 crystallites and significantly weakening the Co–O bond. Due to the function of Ag weakening the Co–O bond, the oxygen vacancies regeneration over the catalyst surface was significantly facilitated under the reaction conditions, which endows the Ag0.04Co(CP) catalyst a much lower activation energy compared with the cobalt oxide for the reaction. Moreover, the Ag0.04Co(CP) catalyst exhibited much stable activity under the presence of 5 vol% O2, 2 vol% H2O and 100 ppmv NO, which is better than that of K doped cobalt oxide reported in literature.

The redox non-innocent ligand 2,2′-bipyrimidine (bpym) reacted with two molar equivalents of LCo(tol) (L = CH(MeCNAr)2, Ar = 2,6-iPr2C6H3) to afford the binuclear CoII complex (LCo)2(μ-bpym) (1), in which the bpym moiety accepts two electrons from the metal centers and in the dianion state. Complex 1 readily underwent one-electron oxidation when treated with [Cp2Fe]+[BPh4]− affording the cation salt [(LCo)2(μ-bpym)][BPh4] (2) with the bpym moiety in the radical anion state. Meanwhile, complex 2 could be converted back to 1 with elemental potassium. The magnetic studies revealed that complex 2 is a single molecular magnet (SMM) under a small external field, while 1 has no SMM activity. This represents a new example of a SMM exhibiting a fully reversible ‘on/off’ switching ability in anodic and neutral states.