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1.
Films of composites of chitosan/poly(aminopropyltriethoxysilane)/poly(ethylene oxide) (CHI/pAPS/PEO) containing a fixed amount of lithium salt are studied. The ternary composition diagram of the composites, reporting information on the mechanic stability, the transparence and the electrical conductivity of the films, shows there is a window in which the molecular compatibility of the components is optimal. In this window, defined by the components ratios CHI/PEO 3:2, pAPS/PEO 2:3 and CHI/PEO 1:2, there is a particular composition Lix(CHI)1(PEO)2(pAPS)1.2 for which the conductivity reaches a value of 1.7 × 10−5 S cm−1 at near room temperature. Considering the balance between the Lewis acid and basic sites available in the component and the observed stoichiometry limits of formed polymer complexes, the conductivity values of these products may be understood by the formation of a layered structure in which the lithium ions, stabilized by the donors, poly(ethylene oxide) and/or poly(aminopropyltriethoxysilane), are intercalated in a chitosan matrix. 相似文献
2.
The ionic conductivity and phase arrangement of solid polymeric electrolytes based on the block copolymer polyethylene-b-poly(ethylene oxide) (PE-b-PEO) and LiClO4 have been investigated. One set of electrolytes was prepared from copolymers with 75% of PEO units and another set was based on a blend of copolymer with 50% PEO units and homopolymers. The differential scanning calorimetry (DSC) results, for electrolytes based on the copolymer with 75% of PEO units, were dominated by the PEO phase. The PEO block crystallinity dropped and the glass transition increased with salt addition due to the coordination of the cation by PEO oxygen. The conductivity for copolymers 75% PEO-based electrolyte with 15 wt% of salt was higher than 10−5 S/cm at room temperature and reached to 10−3 S/cm at 100 °C on a heating measurement. The blend of PE-b-PEO (50% PEO)/PEO/PE showed a complex thermal behavior with decoupled melting of the blocks and the homopolymers. Upon salt addition the endotherms associated with PEO domains disappeared and the PE crystals remained untouched. The conductivity results were limited at 100 °C to values close to 10−4 S/cm and at room temperature values close to 3 × 10−6 S/cm were obtained for the 15 wt% salt electrolyte. Raman study showed that the ionic association of the highly concentrated blend electrolytes at room temperature is not significant. Therefore, the lower values of conductivity in the case of the blend with 50% PEO can be assigned to the higher content of PE domains leading to a morphology with lower connectivity for ionic conduction both in the crystalline and melted state of the PE domains. 相似文献
3.
The structure of the free volume and its temperature dependence between 25 and 200 °C of copolymers of styrene with maleic anhydride, SMA (0-35 mol% MA), is studied by pressure-volume-temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this first part of the work, PVT data are reported which were analysed with the Simha-Somcynsky equation of state to estimate the volume fraction of holes, h, which constitute the excess free volume. The temperature and pressure dependence of the specific volume V, the specific occupied and free volume, Vocc=(1−h)V and Vf=hV, and the corresponding isobaric expansivities and isothermal compressibilities for both the rubbery and glassy state are estimated. We obtained the unexpected results that (i) the occupied volume changes its coefficient of thermal expansion at Tg from αocc,g≈0.5αg≈1×10−4 K−1 below Tg to almost zero (≈0.2×10−4 K−1) above Tg and (ii) the isothermal compressibility of the occupied volume at zero pressure below Tg is rather high, κocc≈2.5×10−4 MPa−1, and decreases only slightly at Tg to about 2×10−4 MPa−1 above Tg. The variation of total, occupied, and free volume parameters with the composition of the SMA copolymers is discussed. 相似文献
4.
New epoxidized soybean oil (ESO)/clay nanocomposites have been prepared with triethylenetetramine (TETA) as a curing agent. The dispersion of the clay layers is investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM data reveal the intercalated structure of ESO/clay nanocomposites has been developed. The thermogravimetric analysis exhibits that the ESO/clay nanocomposites are thermally stable at temperatures lower than 180 °C, with the maximum weight loss rate after 325 °C. The glass transition temperature, Tg, about 7.5 °C measured by differential scanning calorimetry (DSC) and Tg about 20 °C measured by dynamic mechanical study have been obtained. The difference in the Tg between DSC and dynamic measurements may be caused by different heating rate. The nanocomposites with 5-10 wt% clay content possess storage modulus ranging from 2.0×106 to 2.70×106 Pa at 30 °C. The Young's modulus (E) of these materials varies from 1.20 to 3.64 MPa with clay content ranging from 0 to 10 wt%. The ratio of epoxy (ESO) to hydrogen (amino group of TETA) greatly affects dynamic and tensile mechanical properties. At higher amount of TETA, the nanocomposites exhibit stronger tensile and dynamic properties. 相似文献
5.
Pengpeng Li 《Polymer》2007,48(6):1557-1566
The star graft copolymers with three arms composed of poly(ethylene oxide) (PEO) as main chain and polystyrene (PS) as side chains were prepared by sequential anionic ring-opening copolymerization of ethylene oxide and ethoxyethyl glycidyl ether (EEGE), and then atom transfer radical polymerization (ATRP) of styrene. The anionic ring-opening copolymerization of EO and EEGE was carried out using 2-ethyl-2-hydroxymethyl-1,3-propanediol as trifunctional initiator and diphenylmethyl potassium (DPMK) as deprotonating agent. The resulting three-arm star copolymer [poly(EO-co-EEGE)]3 could be easily hydrolyzed to unmask the pendant hydroxyl groups without affecting the PEO chains. The switch from the first to the second mechanism was completed by the reaction of the multi-pendant hydroxyl groups of three-arm PEO chain with 2-bromoisobutyryl bromide. The obtained poly(ethylene oxide-co-2-bromoisobutyryloxyglycidyl ether), [poly(EO-co-BiBGE)]3, was used as macroinitiators to initiate the polymerization of styrene in bulk at 90 °C by ATRP. The final products and intermediates were characterized by NMR, SEC and IR in detail. The amphiphilic star graft copolymers synthesized can form micelles in water. The critical micelle concentration (cmc) determined by fluorescence spectra was about 5 × 10−7 g/mL. Sphere micelles were observed by transmission electron microscopy (TEM) at low copolymer concentration (6 × 10−5 g/mL), but the micelle shape became irregular when the copolymer concentration increased to 6 × 10−4 g/mL. 相似文献
6.
The crystal structure, phase transition and thermal expansion behaviors of solid solutions Sc2−xCrxMo3O12 (0≤x≤2) were investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). At room temperature, samples with x≤0.7 and x≥0.8 crystallize in orthorhombic and monoclinic structures, respectively. DSC result indicates that the phase transition of Sc0.5Cr1.5Mo3O12 from monoclinic to orthorhombic structure occurs at 203.66 °C. The linear thermal expansion coefficient of orthorhombic phases varies from −2.334×10−6 °C−1 to 0.993×10−6 °C−1 when x increases from 0.0 to 1.5. The near-zero linear thermal expansion coefficients of −0.512×10−6 °C−1 and −0.466×10−6 °C−1 are observed for compounds with x=0.5 and 0.7, respectively. 相似文献
7.
The La2−xAxMo2O9−δ (A = Ca2+, Sr2+, Ba2+ and K+) series has been synthesised as nanocrystalline materials via a modification of the freeze-drying method. The resulting materials have been characterised by X-ray diffraction (XRD), thermal analysis (TG/DTA, DSC), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The high-temperature β-polymorph is stabilised for dopant content x > 0.01. The nanocrystalline powders were used to obtain dense ceramic materials with optimised microstructure and relative density >95%. The overall conductivity determined by impedance spectroscopy depends on both the ionic radius and dopant content. The conductivity decreases slightly as the dopant content increases in addition a maximum conductivity value was found for Sr2+ substitution, which show an ionic radii slightly higher than La3+ (e.g. 0.08 S cm−1 for La2Mo2O9 and 0.06 S cm−1 for La1.9Sr0.1Mo2O9−δ at 973 K). The creation of extrinsic vacancies upon substitution results in a wider stability range under reducing conditions and prevents amorphisation, although the stability is not enhanced significantly when compared to samples with higher tungsten content. These materials present high thermal expansion coefficients in the range of (13-16) × 10−6 K−1 between room temperature and 753 K and (18-20) × 10−6 K−1 above 823 K. The ionic transport numbers determined by a modified emf method remain above 0.98 under an oxygen partial pressure gradient of O2/air and decreases substantially under wet 5% H2-Ar/air when approaching to the degradation temperature above 973 K due to an increase of the electronic contribution to the overall conductivity. 相似文献
8.
Nano-γ-Al2O3 is dispersed onto the glass carbon electrode (GCE) by polishing. This nanostructured modified GCE exhibits a great enhancement to the redox responses of 3-nitrobenzaldehyde thiosemicarbazone (3-NBT). In comparison with bare GCE, 3-NBT gives a more sensitive voltammetric response because of the nanoparticle’s unique properties. The lowest detectable concentration (3σ) of 3-NBT is estimated to be 1.18 × 10−6 M (accumulation for 4 min). The linear relationship between peak current and concentration of 3-NBT holds in the range 1.0 × 10−5 M to 1.0 × 10−4 M (r = 0.9981). The electrochemical properties of 3-NBT on this modified electrode have been investigated with various electrochemical methods. The results indicate that the transference of one electron and one proton involves electrode radical reaction processes I and II, respectively. The coverage value (Γ) of 1.62 × 10−9 mol cm−2 was calculated and the electrochemical parameters, diffusion coefficient D (2.54 × 10−3 cm2 s−1, 2.03 × 10−3 cm2 s−1) and reaction rate constant ks (5.9573 s−1, 7.15 × 10−2 cm s−1) were obtained for quasi-reversible system I and irreversible system II, respectively. 相似文献
9.
The X-ray diffraction patterns of (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics were measured within 15–850 K temperature range. The anomaly in the thermal expansion temperature dependence occurred in 250–365 K range. The generalised Cole–Cole model was proposed to describe the measured effective electric permittivity influenced by high electric conduction and the coexistence of two contributions ?*(T,f) = ?*lattice + ?*carriers was considered. The analysis of the electric permittivity and conduction exhibited two relaxation processes. The electric conduction relaxation characteristic time values indicated the small polaron mechanism with τ0 ≈ 10−13 s occurring in 240–345 K range and the ionic mechanism with τ0 ≈ 10−11 s involved in the other relaxation occurring in the 320–510 K range. The ionic relaxation process was ascribed to a subsystem of defects, which was weakly interrelated to the anomaly in thermal expansion of the (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics. The Gate model was proposed to describe the ionic relaxation mechanism. 相似文献
10.
In this study, the effects of CaTiO3 addition on the sintering characteristics and microwave dielectric properties of BiSbO4 were investigated. Pure BiSbO4 achieved a sintered density of 8.46 g/cm3 at 1100 °C. The value of sintered density decreased with increasing CaTiO3, and sintering at a temperature higher than 1100 °C led to a large weight loss (>2 wt%) caused by the volatile nature of the compound. Samples either sintered above 1100 °C or with a CaTiO3 content exceeding 3 wt% showed poor densification. SEM micrographs revealed microstructures with bimodal grain size distribution. The size of the smaller grains ranged from 0.5 to 1.2 μm and that of the larger grains between 3 and 7 μm. The microwave dielectric properties of the (1−x) BiSbO4−x CaTiO3 ceramics are dependent both on the x value and on the sintering temperature. The 99.0 wt% BiSbO4–1.0 wt% CaTiO3 ceramic sintered at 1100 °C reported overall microwave dielectric properties that can be summarized as εr≈21.8, Q×f≈61,150 GHz, and τf≈−40.1 ppm/°C, all superior to those of the BiSbO4 ceramics sintered with other additives. 相似文献
11.
Au nanoparticles (AuNPs) are good quenchers once they closely contact with luminophore. Here we reported a simple approach to obtain enhanced electrogenerated chemiluminescence (ECL) behavior based on Au/CdS nanocomposite films by adjusting the amount of AuNPs in the nanocomposite. The maximum enhancement factor of about 4 was obtained at an indium tin oxide (ITO) electrode in the presence of co-reactant H2O2. The mechanism of this enhancement was discussed in detail. The strong ECL emission from Au/CdS nanocomposites film was exploited to determine H2O2. The resulting ECL biosensors showed a linear response to the concentration of H2O2 ranging from 1.0 × 10−8 to 6.6 × 10−4 mol L−1 with a detection limit of 5 nmol L−1 (S/N = 3) and good stability and reproducibility. 相似文献
12.
Thermal hydrocracking and catalytic hydrocracking over NiMo/γ-Al2O3 of a pentane-insoluble asphaltene were conducted in a microbatch reactor at 430 °C. The experimental data of asphaltene conversion fit second-order kinetics adequately, to give the apparent rate constants of 2.435 × 10−2 and 9.360 × 10−2 wt frac−1 min−1 for the two processes respectively. A three-lump kinetic model is proposed to evaluate rate constants of parallel reactions from asphaltenes to liquid oil (k1) and to gas + coke (k3), and consecutive reaction from liquid to gas + coke (k2). The evaluated k1 is 2.430 × 10−2 and 9.355 × 10−2 wt frac−1 min−1, k2 is 2.426 × 10−2 and 6.347 × 10−3 min−1, and k3 is 5.416 × 10−5 and 4.803 × 10−5 wt frac−1 min−1 for asphaltenes hydrocracking in the presence or absence of the catalyst, respectively. Analysis of selectivity shows that the catalytic hydrocracking process promotes liquid production and inhibits coke formation effectively. 相似文献
13.
A pentane-insoluble asphaltene was processed by thermal cracking and catalytic hydrocracking over NiMo/γ-Al2O3 in a microbatch reactor at 430 °C. Kinetic analysis shows that the first-order kinetics fits the data of conversion in reaction times ≤ 30 min approximately, but deviates from the data of times over 30 min significantly; whereas the second-order kinetics fits the data of the reaction times up to 60 min adequately, to give the apparent rate constants of 1.704 × 10−2 and 9.360 × 10−2 wt frac−1min−1 for the two cracking processes. Furthermore, a three-lump kinetic model is proposed to include parallel reactions of asphaltenes to produce liquid oil (k1) and gas + coke (k3), and consecutive reaction from liquid to gas + coke (k2). The evaluated value of k1 is 1.697 × 10−2 and 9.355 × 10−2 wt frac−1min−1, k2 is 3.605 × 10−2 and 6.347 × 10−3 min−1 , and k3 is 6.934 × 10−5 and 4.803 × 10−5 wt frac−1min−1 for asphaltenes thermal cracking and catalytic hydrocracking, respectively. Selectivity analysis shows that the catalytic hydrocracking process promotes liquid production and inhibits coke formation effectively. 相似文献
14.
Electrochemical behavior of lithium intercalated in a molybdenum disulfide-crown ether nanocomposite
A new nanocomposite, obtained from the intercalation of the cyclic ether 12-Crown-4 into MoS2, Li0.32MoS2(12-Crown-4)0.19, is described. The laminar product has an interlaminar distance of 14.4 Å. The electrical conductivity of the nanocomposite varies from 2.5 × 10−2 to 4.3 × 10−2 S cm−1 in the range 25-77 °C, being about four times higher than the analogous poly(ethylene oxide) (PEO) derivative at room temperature. The electrochemical step-wise galvanostatic intercalation or de-intercalation of lithium, leading to LixMoS2(12-Crown-4)0.19 with x in the range 0.07-1.0, indicates a Li/Li+ pair average potential of 2.8 V. The electrochemical lithium diffusion coefficients in the crown ether intercalates, determined by galvanostatic pulse relaxation between 15 and 37 °C at different lithium intercalation degrees, are higher than those of the PEO derivatives under similar conditions, being however the diffusion mechanism rather more complex. The variation of both, the lithium diffusion activation enthalpy and the quasi-equilibrium potentials, with the lithium content shows there are two different limit behaviors, at low and high lithium intercalation degree, respectively. These features are discussed by considering the high stability of the Li-crown ether complex and the different chemical environments found by lithium along the intercalation process. 相似文献
15.
Polystyrene-layered silicate nanocomposites were prepared from three new organically modified clays by emulsion polymerization method. These nanocomposites were exfoliated up to 3 wt% content of pristine clay relative to the amount of polystyrene (PS). The intercalated agents C20, C20-4VB, and C20-POSS intercalated into the galleries result in improved compatibility between hydrophobic polymer and hydrophilic clay and facilitate the well dispersion of exfoliated clay in the polymer matrix. Results from X-ray diffraction, TEM and Fourier transform infrared spectroscopy indicate that these intercalated agents are indeed intercalated into the clay galleries successfully and these clay platelets are exfoliated in resultant nanocomposites. Thermal analyses of polystyrene-layered silicate nanocomposites compared with virgin PS indicate that the onset degradation temperature ca. 25 °C increased and the maximum reduction in coefficient of thermal expansion (CTE) is ca. 40% for the C20-POSS/clay nanocomposite. In addition, the glass transition temperatures of all these nanocomposites are higher than the virgin PS. 相似文献
16.
This paper describes the synthesis and characterization of three-dimensional hybrid inorganic-organic networks prepared by a polycondensation reaction between Zr(O(CH2)3CH3)4 and polyethylene glycol 400 (PEG400). Eleven hybrid networks doped with varying concentrations of LiClO4 salt were prepared. On the basis of analytical data and FT-Raman studies it was concluded that these polymer electrolytes consist of inorganic-organic networks with zirconium atoms bonded together by PEG400 bridges. These polymers are transparent with a solid rubber consistency and are very stable under inert atmosphere. Scanning electron microscopy revealed a smooth glassy surface. X-ray fluorescence microanalysis with energy dispersive spectroscopy demonstrated that all the constituent elements are homogeneously distributed in the materials. Thermogravimetric measurements revealed that these materials are thermally stable up to 262 °C. Differential Scanning Calorimetry measurements indicated that the glass transition temperature Tg of these inorganic-organic hybrids varies from −43 to −15 °C with increasing LiClO4 concentration. FT-Raman investigations revealed the TGT (T=trans, G=gauche) conformation of polyether chains and allowed characterization of the types of ion-ion and ion-polymer host interactions in the bulk materials. The conductivity of the materials at different temperatures was determined by impedance spectroscopy over the 20 Hz-1 MHz frequency range. Results indicated that the materials conduct ionically and that their ionic conductivity is strongly influenced by the segmental motion of the polymer network and the type of ionic species distributed in the bulk material. Finally, it is to be highlighted that the hybrid network with a nLi/nO molar ratio of 0.0223 shows a conductivity of ca. 1×10−5 S cm−1 at 40 °C. 相似文献
17.
The micro-structural, compositional, temperature dependent dielectric and electrical properties of the Bi1.5Zn0.92Nb1.5−xTaxO6.92 solid solution has been investigated. The increasing Ta content from 0.2 to 1.5 caused; single phase formation, a pronounced grain size reduction from ∼7.0 to 2.5 μm, sharp decrease in the dielectric constant from 198 to 88 and an increase in the electrical conductivity from 3.16 × 10−10 to 5.0 × 10−9 (Ω cm)−1, respectively. The temperature dependent dielectric constant which is found to be frequency invariant in the frequency range of (0.0-2.0 MHz) exhibited a sharp change in the temperature coefficient of dielectric constant at a (doping independent) critical temperature of 395 K. The analysis of the measured data reflects a promising future for this type of pyrochlore to be used in high voltage passive device applications. 相似文献
18.
Water-soluble amino acid derivatives of gadolinium (Gd) endohedral metallofullerenes (AAD-EMFs), Gd@C82Om(OH)n(NHCH2CH2COOH)l (m ≈ 6, n ≈ 16 and l ≈ 8) are synthesized by a direct reaction of the pure endohedral metallofullerene Gd@C82 with an excess of alkaline solution of β-alanine. The structure of the AAD-EMFs is characterized by FTIR, XPS and laser-desorption time-of-flight (LD-TOF) mass spectrometries. Water proton relaxivity analysis indicates that the longitudinal relaxivity R1 (the effect on 1/T1, 9.1 mM−1 s−1) of AAD-EMFs is higher than that of the commercial MRI contrast agent, Magnevist (gadolinium-diethylenetriaminepentaacetic acid, Gd-DTPA, 5.6 mM−1 s−1). The MRI phantom studies are performed to confirm the high efficiency of this sample as MRI contrast agents. 相似文献
19.
Bertel Kastening 《Electrochimica acta》2005,50(12):2487-2498
The dependence of the composition of aqueous electrolytes in the pore system of activated carbon on the potential has been determined by monitoring the amount of ions exchanged with the external electrolyte upon immersion and upon changing the electrode potential. From the investigation with KF solutions, a quantity δ/√? = 4 × 10−10 m is evaluated where δ is half the width of the micropores, and ? the (relative) permittivity. This is in accordance with δ ≈ 1 nm and ? ≈ 7 applying to essentially immobilized water and fits into the results with the other electrolytes. Anions are adsorbed in the cases of sodium perchlorate and potassium hydroxide, while protons are adsorbed in the case of acids (HCl, H2SO4). The adsorption of ClO4− seems to result from electrostatic interaction with the solid, while H+ and OH− are strongly chemisorbed, probably at surface groups like >CO. Ionic mobilities of ions in the micropores have been determined from conductance measurements concerning the pore electrolyte of a single spherical particle of activated carbon. Mobilities are more than one order of magnitude lower than those in bulk electrolyte, probably due to an increased viscosity of the liquid in the narrow pores and/or to the coulombic interaction with charged domains of the solid. The rate of charging of the capacitor (solid/micropore electrolyte) is assisted by macropores distributing ions throughout the carbon material. 相似文献
20.
5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H2SO4 between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s−1. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L−1 phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10−7 mol L−1 to 3 × 10−5 mol L−1. The electrode had a detection limit of 6.0 × 10−8 mol L−1(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s−1, the transfer coefficient α = 0.709, the electron number involved in the rate determining step nα = 0.952, and the diffusion coefficient Do = 3.54 10−5 cm2 s−1 were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation. 相似文献