Electrostatic layer-by-layer assembled carbon nanotube multilayer film and its electrocatalytic activity for O2 reduction

Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions.     

Insertion Reactions of Carbon Disulfide into Mg‐C and Mg‐N Bonds: Syntheses and Structural Determinations of Mg(S2CY)2(THF)n(Y=NEt2, NiPr2, iPr,Ph) and BrMg(S2CZ)(THF)3(Z=Ph,iPr)

The insertion reaction of CS₂ with Mg(NR₂)₂ (R= Et, ⁱPr), MgR′₂ (R′= Et, Ph) and R″MgBr (R″= ⁱPr, Ph) respectively lead solid products, Mg(S₂CNR₂)₂(THF)_n ( 1 : R= Et, n=2; 2 : R= ⁱPr, n=1), Mg(S₂C′R)₂(THF)₂ ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S₂C″R) (THF)₃ ( 5 : ″R= ⁱPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with ¹H, ¹³C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography.     

Interaction and adhesion properties of polyelectrolyte multilayers

The growth, morphology, and interaction/adhesion properties of supported poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride) (PSS/PAH) and DNA/PAH multilayers were investigated by means of surface plasmon resonance spectroscopy, atomic force microscope (AFM) imaging, and AFM-related force measurements. Multilayers were assembled on a prelayer of poly(ethylenimine) (PEI) both with and without drying. SPR results showed a linear growth of the assembly in the case of PSS/PAH multilayers and nonlinear growth for DNA/PAH multilayers. Measurements of forces acting between a bare glass sphere and a multilayer-coated surface indicated repulsive or attractive forces, depending on surface charge, which suggests that, on approach, electrostatic forces dominate. On separation, we observed large pull-off forces in the case of positively charged multilayers and weak pull-off forces in the case negatively charged multilayers. Multiple adhesions and plateau regions observed on separation were interpreted in terms of a bridging of multiple polymer chains between the glass particle and the multilayer and a stretching of the polyelectrolyte loops. The dependence of the pull-off force on the number of deposited layers shows regular oscillations.     

Curing behavior and toughening performance of epoxy resins containing hyperbranched polyester

The effects of the hyperbranched polyester with hydroxyl end groups (HBPE‐OH) on the curing behavior and toughening performance of a commercial epoxy resin (diglycidyl ether of bisphenol A, DGEBA) were presented. The addition of HBPE‐OH into DGEBA strongly increased its curing rate and conversion of epoxide group due to the catalytic effect of hydroxyl groups in HBPE‐OH and the low viscosity of the blend at curing temperature. The improvements on impact strength and critical stress intensity factor (or fracture toughness, K_1c) were observed with adding HBPE‐OH. The impact strength was 8.04 kJ m^?1 when HBPE‐OH reached 15 wt% and the K_1c value was approximately two times the value of pure epoxy resin when HBPE‐OH content was 20 wt%. The morphology of the blends was also investigated, which indicated that HBPE‐OH particles, as a second phase in the epoxy matrix, combined with each other as the concentration of HBPE‐OH increased. Copyright © 2004 John Wiley & Sons, Ltd.     

Imaging cellular distribution of fluorescent supramolecular nanofibers

In this study, we used the 4-nitro-2,1,3-benzoxadiazole (NBD) as an aromatic capping group for a peptide to construct the supramolecular nanofibers. Taking the advantage of the fluorescence property of NBD, we could directly observe the cellular distribution of the self-assembled nanofibers. We found that the distributions of the nanofibers of NBD-FFETIGGY are different in four mammalian cells and two plant cells. The nanofibers are mainly located at the surface of two mammalian cells and one plant cell, while in the intracellular space of other cells. Different distributions of nanofibers lead to different protein binding patterns of the nanofibers in two different cell lines. We believe that a useful and versatile platform has been offered to the image cellular distribution of nanofibers, which can provide useful information to the biological functions of the self-assembled nanostructures.     

Assembly of peptide–thiophene conjugates: the influence of peptide content and location

Biomolecule-directed self-assembly of π-conjugated oligomers has attracted great attention in the past decade. In this contribution, two conjugates composed of quaterthiophene and tetrapeptide (Gly-Val-Gly-Val) were synthesised, namely peptide–thiophene–peptide (PTP) and thiophene–peptide–thiophene (TPT), to investigate the influence of peptide content ratio and its location in the molecular structures on the nanostructures and properties of the assemblies. Both conjugates formed organogels consisting of left-handed twisted nanostructures; however, anti-parallel β-sheets were observed in PTP while parallel β-sheets were obtained for TPT, although in both cases oligothiophenes adopted an H-like stacking mode. Obvious solvent-induced supramolecular chirality inversion from the oligothiophene segment was observed for PTP while such phenomenon was not clear for TPT. PTP and TPT gels also showed different stabilities towards temperature increase, as evidenced by variable-temperature circular dichroism study. From the data, it is suggested that the rational design of the location and ratio of peptide plays a key role in constructing materials with determined properties based on peptide–thiophene conjugates.     

Sustainable cationic cellulose for highly efficient flocculation of Kaolin suspension

Cellulose - Green bio-flocculants from renewable biomass resources have received the widespread attention for wastewater treatment, which are promising alternatives to petroleum-based synthetic...     

Effects of Cr and V impurities on cohesion properties of Pd/TiAl interfaces

First principles calculations reveal that for Pd/TiAl interfaces the substitution of interface Ti atoms with Cr or V atoms is energetically favorable with negative heat of formation, and could bring about a very small increase of interface bond strength, while the interstitial Cr and V atoms should be unfeasible with highly positive heat of formation and would increase the bond lengths of interface Pd–Al and Pd–Ti bonds. Calculations also demonstrate that both Cr and V would induce an increase of interface energy, suggesting that the impurity atoms of Cr or V should be reduced to a minimum level, in order to get a thermally stable Pd/TiAl interface with a longer lifetime. In addition, it is found that the substitution of V at the Pd/TiAl interfaces should be much easier than that of Cr, which is in good agreement with similar experimental observations in the literature.     

Attapulgite grafted with polystyrene via a simultaneous reverse and normal initiation atom transfer radical polymerization

The surface grafting of attapulgite (ATP) with polystyrene (PS) was established via a simultaneous reverse and normal initiation atom transfer radical polymerization (SR&NIATRP). 4‐(chloromethyl)phenyltrimethoxysilane (CMPTMS) chemical bounded on the surface of ATP (ATP‐Cl, Cl‐I) was prepared via one‐step self‐assembly. SR&NI ATRP of styrene was conducted using CuCl₂ complex tris(2‐(dimethylamino)ethyl)amine (Me₆‐TREN) as the catalytic system, initiated by 2,2‐azobis(isobutyronitrile) (AIBN) and ATP‐Cl. FT‐IR, XRD, XPS, TGA and TEM data were consistent with the grafting of benzyl chloride groups and PS chains on ATP surface. The controllability of polymerization was investigated by the kinetics behavior under different molar ratio of AIBN and CuCl₂. The obtained polymer possessed a uniform distribution of molecular weights with a lower polydispersity index of 1.2～1.4. The relationship between polymerization on the surface of ATP and in solution was discussed in detail based on TGA data of hybrid particles and GPC trace of free polymer in solution. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1508–1516