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1.
The formation of complexes at pH 4.7 of the Hg(II) with five monothiosemicarbazone and two dithiosemicarbazone has been studied. The mercury(II) reacts with monothiosemicarbazones of salicylaldehyde (λmax = 363 nm, E = 1.69 × 104liters · mol?1cm?1), pi-colinadehyde (λmax = 363 nm, E = 2.38 × 104liters · mol?1cm?1), 6-methyl-picolinaldehyde (λmax = 363 nm, E = 2.28 × 104liters · mol?1cm?1), di-2-pyridylketone (λmax = 380 nm, E = 2.08 × 104liters · mol?1cm?1), and o-naphthoquinone (λmax = 540 nm, E = 1.03 × 104liters · mol?1cm?1) and with dithiosemicarbazones of 1,4-dihydroxyphthalimide (λmax = 430 nm, E = 2.56 × 104liters · mol?1cm?1) and dipyridylglyoxal (λmax = 363 nm, E = 2.37 × 104liters · mol?1cm?1). A critical comparison of the stoichiometry and apparent stability constant of complexes with mono- and dithiosemicarbazones is given.  相似文献   

2.
Low-angle electron diffraction (LAED) was used to study the microstructure of crazes produced at different temperatures T and strain rates in thin films of monodisperse polystyrene (PS). At a slow strain rate of 4.1 × 10?6 s?1 both the fibril diameter D and the fibril spacing D0 of crazes in 1800k molecular weight PS remained constant with temperature up to T ≈ 70°C and then sharply increased as T approaches Tg. At a higher strain rate of ~ 10?2 s?1, both D and D0 increase only slightly with T. The values of D and D0 over a range of temperature are in very good agreement with those values obtained in bulk samples using small-angle x-ray scattering. The crazing stress was measured as a function of temperature in the thin films of the 1800k molecular weight PS strained at the same slow strain rate used for the LAED measurements. These measurements were analyzed using a simple model of craze growth to reveal the temperature and strain rate dependence of the craze surface energy Γ. At room temperature Γ ≈ 0.076 J/m2 (versus Γ ≈ 0.087 J/m2 predicted) and was observed to remain constant up to T ≈ 70°C and then decrease by approximately a factor of two at T = 90°C. This decrease in Γ is believed to result from chain disentanglement to form fibril surfaces at sufficiently high temperatures and occurs in the same temperature range in which the craze fibril extension ratio λ was observed to increase.  相似文献   

3.
Data on tensile strength and elongation at break for a series of Viton A-HV vulcanizates are discussed. The data were obtained at various extension rates at temperatures from ?5 to 230°C (25 ? TTg ? 260°C) on seven vulcanizates having crosslink densities ve (estimated from C1 in the Mooney-Rivlin equation) from 0.46 × 10?5 to 24.4 × 10?5 mole/cm3. At an extension rate of 1 min?1, an increase in ve affects the tensile strength σb (based on the undeformed cross-sectional area) and the true tensile strength σbσb (based on the cross-sectional area of a deformed specimen) as follows: σb is essentially constant at a low temperature; it passes through a decided maximum at intermediate temperatures; and it increases to a plateau at elevated temperatures. In contrast, λbσb decreases markedly at all temperatures, an exception being the most lightly crosslinked vulcanizate(s). Application of time—temperature superposition to the ultimate-property data gave log aT; its temperature dependence is that typical of nonpolar rubbery polymers. Data on the vulcanizates were compared in corresponding temperature states by plotting log 273σb/T, log 273λbσb/T, and (λb — 1)/(λb — 1)max against logtb/(tb)max, where tb is the temperature-reduced time to break and (tb)max is the value at which the ultimate extension ratio λb attains its maximum, (λb)max. Except for the most lightly crosslink vulcanizate, the comparison shows that 273λbσb/T and (λb — 1)/(λb — 1)max are substantially independent of (or only weakly dependent on) crosslink density, that 273λb/T increases with ve, and that 273λb/T ∝? ve0.6 and λb ∝? ve?0.4 at a large value of tb/(tb)max.  相似文献   

4.
The rheological behavior of an uncrosslinked polybutadiene on sudden application of finite strain was examined. The shear stress σ, two components of birefringence, and the extinction angle were measured in shear (magnitude of shear γ ≤ 3.5) and tensile stress and the birefringence were measured in uniaxial elongation (elongation ratio λ ≤ 3.8). Measurements were performed at 30°C with a tensile tester equipped with appropriate sample holders. The stress-optical coefficient was 3.01 × 10?9Pa?1. The first and second normal-stress differences v1 and v2 were separately evaluated with the use of stress-optical law. The Lodge—Meissner relation v1 = γσ held good. The ratio v2/v1 was independent of time and varied from about ?0.3 to ?0.2 with increasing γ in the range of measurements. Each of the stress components was factored into a function of strain and one of time, and the latter was common to all the stress components. Simple formulas were proposed to represent stress components in step deformations.  相似文献   

5.
Blue diode‐based pulse amplitude modulation (PAM) technology can be used to measure the photosynthetic electron transport rate (ETR) in a purple nonsulfur anoxygenic photobacterium, Afifella (Rhodopseudomonas) marina. Rhodopseudomonads have a reaction center light harvesting antenna complex containing an RC‐2 type bacteriochlorophyll a protein (BChl a RC‐2‐LH1) which has a blue absorption peak and variable fluorescence similar to PSII. Absorptance of cells filtered onto glass fiber disks was measured using a blue–diode‐based absorptance meter (Blue‐RAT) so that absolute ETR could be calculated from PAM experiments. Maximum quantum yield (Y) was ≈0.6, decreasing exponentially as irradiance increased. ETR vs irradiance (P vs E) curves fitted the waiting‐in‐line model (ETR = (ETRmax × E/Eopt) × exp(1 ? E/Eopt)). Maximum ETR (ETRmax) was ≈1000–2000 μmol e? mg?1 BChl a h?1. Fe2+, bisulfite and thiosulfate act as photosynthetic electron donors. Optimum irradiance was ≈100 μmol m?2 s?1 PPFD even in Afifella grown in sunlight. Quantum efficiencies (α) were ≈0.3–0.4 mol e? mol hλ?1; or ≈11.8 ± 2.9 mol e? mol hλ?1 m2 μg?1 BChl a). An underlying layer of Afifella in a constructed algal/photosynthetic bacterial mat has little effect on the measured ETR of the overlying oxyphotoautotroph (Chlorella).  相似文献   

6.
A simple sensitive spectrophotometric method has been developed for the determination of atrazine in herbicide formulations and real samples. The method was based on the reaction of atrazine with pyridine to form a quaternary halide which in the presence of alkali forms a carbinol base. The heterocyclic ring of the carbinol base breaks and forms the glutaconic dialdehyde. The glutaconic dialdehyde group was coupled with sulfanilic acid to form a yellow coloured product having λ max 450 nm or coupled with aniline to form a orange red coloured product having λ max 480 nm. The Beer's law was obeyed over the range from 0.1 to 25 µg mL?1 and molar absorptivity 1.5 × 104 L mol?1 cm?1 for sulfanilic acid, and from 0.08 to 12 µg mL?1 and molar absorptivity 1.3 × 104 L mol?1 cm?1 for aniline were observed. The reaction conditions and other analytical parameters were optimised. The proposed method has been successfully applied for the analysis of commercial formulations and real samples.  相似文献   

7.

The rheological behavior of dope solutions of poly(acrylonitrile‐co‐itaconic acid) or poly(AN‐co‐IA) is important from the point of view of deriving the spinning conditions for good quality special acrylic fibers. The viscosity of the resin dope is dictated by the polymer concentration, molar mass, temperature and shear force. The dynamic shear rheology of concentrated poly(AN‐co‐IA) polymer dope solutions in N, N‐dimethylformamide, in the molar mass (M¯v) range of 1×105 to 1×106 g/mol, was investigated in the shear rate (γ′) range of 1×101 to 5×104 min?1. An empirical relation between η and M¯v was found to exist at constant shear rate. The dope viscosity was dependent on the molar mass and the shear rate at a given temperature (T) and concentration. The polymer molar mass index of dope viscosity (m) was calculated as functions of concentration (c), shear rate and temperature. The m values increased with shear rate and temperature. A master equation relating m, with shear rate and temperature was derived for a given dope concentration. At higher shear rates, m tends to the value of 3.4, which is close to the molar mass index of viscosity reported for molten thermoplastics. m increased significantly with shear rate and nominally with temperature, while an increase in concentration decreased it. The onset of shear thinning of the dope shifted to a lower shear rate regime with an increase in polymer concentration and the molar mass. For a given value of molar mass, the increase in viscosity of the dope solution with polymer concentration was dependent on the shear rate.  相似文献   

8.
Abstract

The complex μ-TEPP-trans-bis[P(OEt)3Ru(NH3)4]2(PF6)4 has been prepared and characterized by microanalysis, vibrational and electronic spectroscopy (λmax=299 nm, ?=6.4 × 102 M?1 cm?1; λmax=262 nm, ?=8.6 × 102 M?1 cm?1), and cyclic voltammetry (E°'=+0.64 V versus S.C.E., 25°, μ=0.10 M NaCf3COO, CH+=1 × 10?3 M). In aqueous solutions, ([H+] > 1 × 10?4 M), the binuclear species undergoes hydrolysis yielding the mononuclear species trans-(Ru(NH3)4P(OEt)3(H2O)]2+ with a specific rate constant of 2.4 × 10?5 sec?1 at 25° δH#=84.5 kJ mol?1; δS#=?49.4 J mol?1 K?1.  相似文献   

9.
2,2′-Dihydroxybenzophenone thiosemicarbazone forms complexes with Cu(II) (λmax = 385 nm, ? = 8.60 × 103 liter · mol?1 · cm?1); Ni(II) (λmax = 380 nm, ? = 15.4 × 103 liter · mol?1 · cm?1); Co(II) (λmax = 380 nm, ? = 12.3 × 103 liter · mol? · cm?1); and Fe(III) (λmax = 365 nm, ? = 7.9 × 103 liter · mol?1 · cm?1) and have been applied to the analysis of these metal ions in binary, ternary, and quaternary mixtures. The determination procedures are based exclusively on the different pH values of the formation complexes, hence the extraction step is not necessary.  相似文献   

10.
With a view to the use of picolinealdehyde salicyloylhydrazone as analytical reagent, a study of the physical properties and chemical reactions of this substance has been carried out. It reacts with nickel (λmax = 375 nm, ? = 3.9 × 104M?1cm?1) or zinc (λmax = 365 nm, ? = 4.8 × 104M?1cm?1) to produce a yellow 1:2 complex in both cases. Spectrophotometric determinations of trace amounts of nickel and zinc have been established.  相似文献   

11.
Models for rubber particle cavitation, shear yielding, and crazing are reviewed, and their ability to predict the large-strain deformation behavior of toughened polymers is discussed. An existing model for void initiation and expansion in rubber particles correctly predicts the observed trends: cavitation resistance increases when either the shear modulus or the surface energy of the rubber is increased, or the particle size is reduced. However, further work is needed to improve quantitative modeling of the thermally- and stress-activated void nucleation step. Shear yielding, which is also a rate process, is much better understood; here, the main problems in modeling relate to the formation and evolution of porous shear bands. Craze growth and failure are also reasonably well understood, but previous attempts at modeling have been hampered by uncertainties about craze initiation. To overcome these difficulties, a new theory of crazing is proposed, which treats initiation as a fracture process, and defines a new materials property, Gnasc, the energy required to form unit area of nascent craze. Because nascent crazes are ∼20 nm thick, Gnasc is low: calculations give values <0.5 J m−2 for polystyrene. A new criterion incorporating a plasticity factor fits the data of Sternstein and coworkers on crazing under biaxial loading. In combination with theories of particle cavitation and shear yielding, the fracture mechanics model explains why the balance between crazing and shear yielding is governed by particle size, for example in ABS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1399–1409, 2007  相似文献   

12.
张洪林  于秀芳  聂毅  刘晓静  张刚 《中国化学》2003,21(11):1466-1469
IntroductionMostcomplicatedreactionshappenedinlivingcrea tures ,amongthemenzymecatalyzedreactionisanimpor tantclass .Itissignificantinboththeoryandpracticetoinvestigateenzymecatalyzedreaction .Therearemanyex perimentalmethodssuchasspectrophotometry ,titrimetry ,isotopemethod ,microcalorimetryandsoon ,inwhichmi crocalorimetryisanewoneduetoitshighsensitivityandaccuracy .Wecanstudythewholeprocessoftheheatef fectusingamicrocalorimeter .Sincetheabsorptionorpro ductionofheatisanintrinsicpropertyofe…  相似文献   

13.
Abstract

Cholesteric liquid crystals which have a helical arrangement of oriented chiral molecules are expected to show novel cross couplings between fluxes and forces. The most convincing demonstration of these couplings is through a dynamical effect on the structure. Though Lehmann found a rotation of the structure under a temperature gradient in 1900, there has been no subsequent experiment confirming the same. We argue that it is very difficult to obtain a sufficiently weak anchoring of the director at the solid-cholesteric interface which is a necessary condition for the occurrence of Lehmann rotation. In order to achieve a practically zero anchoring energy at the surface, we have devised a simple technique of floating essentially flat cholesteric drops in the isotropic phase. Using this configuration we study the electromechanical coupling which produces a rotation of the structure under the action of a DC electric field. Using measurements on samples with different values of the pitch the relevant electromechanical coefficient of the materials investigated is found to satisfy the relation v E = ?0·6 × 10?12(q/m?1)J m?2, where q is the wavevector of the helix, whose sign is positive (negative) for a right (left) handed structure, confirming that v E is hydrodynamic in origin.  相似文献   

14.
The decomposition of polybromostyryl carbanions (PBS?), obtained by anionic polymerization of 4-bromostyrene in tetrahydrofuran (THF), was investigated in the dark in a temperature range of ?6–?21°C. It was accompanied by the evolution of bromine anions and by the formation of polymeric allylic carbanions (λmax = 575 nm; εmax = 6800 eq?1·L·cm?1). The reaction mechanism was elucidated. The rate constant of the unimolecular rate-determining step of the process was 1.3 × 10?5 s?1 and 9.7 × 10?5 s?1 at ?21 and ?6°C, respectively. Its apparent energy of activation Eapp = 18.38 Kcal/mol. The polybromostyrenes with allylic carbanions at their ends may decompose further. Their “dark” decomposition yielded 1,3-butadiene-1,3-diphenyl-macromers. The mechanisms of decomposition of the PBS? carbanions and the dark decomposition of the polybromostyryl allylic carbanions are analogous. The rate constant of the latter process was 2.5 × 10?6 s?1 at ?6°C. The anionic polymerization of prepared macromers can be initiated in THF at ?78°C by α-methylstyryl carbanions, which do not react, however, with PBS? carbanions. “Comblike” polymacromers were prepared in which each branch had a molecular weight of about 50,000. The overall molecular weight of the polymacromer was estimated to be about 1 × 106. It has been assumed that the 2–1 mode of addition to the diene group of the macromer is predominant during its polymerization. The 3–4 mode of addition followed by proton shift represents the termination step. The 4–3 mode of addition was ruled out on the basis of spectroscopic evidence.  相似文献   

15.
We demonstrate that Blue‐diode‐based pulse amplitude modulation (PAM) technology can be used to measure the photosynthetic electron transport rate (ETR) of purple sulfur bacteria (Thermochromatium tepidum, Chromatiaceae). Previous studies showed that PAM technology could be used to estimate photosynthesis in purple nonsulfur bacteria and so PAM technology can be used to estimate photosynthesis of both kinds of purple photosynthetic bacteria. The absorptance of Thermochromatium films on glass fiber disks was measured and used to calculate actual ETR. ETR vs Irradiance (P vs E) curves fitted the waiting‐in‐line model (ETR = (ETRmax × E/Eopt) × exp (1?E/Eopt)). Yield (Y) was only ≈ 0.3–0.4. Thermochromatium saturates at 325 ± 13.8 μmol photons m?2 s?1 or ≈15% sunlight and shows photoinhibition at high irradiances. A pond of Thermochromatium would exhibit classic surface inhibition. Photosynthesis is extremely low in the absence of an electron source: ETR increases in the presence of acetate (5 mol m?3) provided as an organic carbon source and also increases in the presence of sulfite (3 mol m?3) but not sulfide and is only marginally increased by the presence of Fe2+. Nonphotochemical quenching does occur in Thermochromatium but at very low levels compared to oxygenic photo‐organisms or Rhodopseudomonads.  相似文献   

16.
In DMSO/water (4:1), photolysis of the dihydroxy-Sn (IV)-mesoporphyrin dimethyl ester (SnP)/methyl viologen (MV2+)/ethylene diamine tetraacetic acid (EDTA) ternary system produces methyl viologen cation radical with a quantum yield of 0.67, much higher than that of systems with other metal complexes of mesoporphyrin dimethyl ester. Neither EDTA nor MV2+ quenches the stationary fluorescence of SnP, implying that the reaction does not take place at the singlet state. With flash photolysis we obtain the T-T absorption spectrum of SnP (λmax 440 nm). By following the decay of this absorption, the triplet life time of SnP is estimated to be 41 μs. The life time is related to the concentration of either MV2+ or EDTA. Good linear relationships are obtained by plotting τ0τ vs. the concentration of MV2+ or EDTA (Stern-Volmer plot), from which we determine the quenching constants: kq(MV2+) =5.5 × 107 mol?1, s?1; kq (EDTA) =2.7 × 107 mol?1, s?1. The data suggests that upon photolysis of the above ternary system, both oxidative quenching and reductive quenching of the triplet state of the sensitizer are occurring. From the measured phosphorescence spectrum (λmax 704 nm) and the ground state redox, potentials (Ered1/2?-0.84V, Eox1/2?+1.43 V, vs. Ag/AgCl, KCl (sat.)), we obtain the redox potential of triplet SnP to be E(P+/P*T)?-0.33 V, E(P*T+/P?)?+0.92 V. Matching this data with the redox potential of MV2+ and EDTA, we establish the fact that during the photolysis of the SnP/MV2+/EDTA ternary system, both oxidative and reductive quenching are thermodynamically favorable processes. This is also the reason why the SnP sensitized reaction is much more efficient relative to other mesoporphyrin derivatives.  相似文献   

17.
The crystalline elastic modulus of poly(cis 1,4-isoprene) has been measured by x rays and calculated by molecular mechanics. The experimental modulus is E = (2.3 ± 0.3) × 109N m?2. The calculated modulus is E = (8.8 ± 0.1) × 109N m?2 for chains in S+ cis S?T conformation and E = (6.1 ± 0.1) × 109N m?2 for chains in S+ cis S+T conformation. The modulus calculated for a statistical structure including both conformation is E = (6.7 ± 0.1) × 109N m?2. The experimental modulus is thought to be a lower limit because of partial crystallinity of the sample. The chief mechanism of deformation is rotation around single bonds adjacent to the double bond.  相似文献   

18.
Stress relaxation has been studied in networks of dihydroxy-terminated polybutadiene (mostly cis:trans:vinyl = 34:40:26) crosslinked by triphenyl methane-4,4′,4″-triisocyanate and containing about 9.5% by weight of unattached linear random styrene-butadiene copolymer with various molecular weights (from 1.4 to 3.3 × 105) and with styrene content and butadiene microstructure chosen to match the average solubility parameter of the end-linked network. Stress relaxation measurements were made also on networks containing no unattached species and containing 9.3% hydrocarbon oil, and on the various uncrosslinked linear polymers. The stretch ratio was 1.25 and the Young's relaxation modulus was calculated from the neo-Hookean stress-strain relation. For the uncrosslinked linear polymers, the relaxation modulus E11(t) corresponds to a rather narrow distribution of relaxation times whose magnitudes were approximately proportional to the 3.4 power of viscosity-average or weight-average molecular weight; for one polymer, the time dependence agreed closely with the prediction of the Doi-Edwards theory modified for a small degree of molecular weight distribution. The disengagement times calculated from the Doi-Edwards theory as modified by Graessley appeared to be of the correct order of magnitude. The contribution of the unattached species in the networks E1(t) was calculated by difference; after multiplication by (1?v)?1, where v2 is the volume fraction of network, and correction for the difference in monomeric friction coefficient associated with the difference in fractional free volume in the two environments, E1(t) was compared with E11(t) for each linear polymer. The relaxation was slower in the network than in the uncrosslinked polymer by about an order of magnitude, but the form of the relaxation modulus was similar in both environments except for two linear polymers for which the relaxation in the network became very much slower at long times. This behavior appeared to be correlated with a broader molecular weight distribution.  相似文献   

19.
Picolinealdehyde salicyloylhydrazone reacts with vanadium(V) to produce a yellow 1:1 complex (λmax = 400 nm, ? = 2.17 × 104 liters · mol?1 cm?1) in aqueous ethanolic solution. The yellow complex can be extracted into chlorobenzene (λmax = 425 nm, ? = 2.16 × 104 liters · mol?1 cm?1) and used for the spectrophotometric determination of trace amounts of vanadium. Interferences have been investigated. The method has been applied to the determination of vanadium in steel and in lead concentrates.  相似文献   

20.
Photosynthetic bacteria are attractive for biotechnology because they produce no oxygen and so H2‐production is not inhibited by oxygen as occurs in oxygenic photoorganisms. Rhodopseudomonas palustris and Afifella marina containing BChl a can use irradiances from violet near‐UV (VNUV) to orange (350–650 nm) light and near‐infrared (NIR) light (762–870 nm). Blue diode‐based pulse amplitude modulation technology was used to measure their photosynthetic electron transport rate (ETR). ETR vs Irradiance curves fitted the waiting‐in‐line model—ETR = (ETRmax × E/Eopt) × exp (1 ? E/Eopt). The equation was integrated over pond depth to calculate ETR of Afifella and Rhodopseudomonas in a pond up to 30 cm deep (A376, 1 cm = 0.1). Afifella saturates at low irradiances and so photoinhibition results in very low photosynthesis in a pond. Rhodopseudomonas saturates at ≈15% sunlight and shows photoinhibition in the surface layers of the pond. Total ETR is ≈335 μmol (e?) m?2 s?1 in NUV + photosynthetically active radiation light (350–700 nm). Daily ETR curves saturate at low irradiances and have a square‐wave shape: ≈11–13 mol (e?) m?2 day?1 (350–700 nm). Up to 20–24% of daily 350–700 nm irradiance can be converted into ETR. NIR is absorbed by water and so competes with the bacterial RC‐2 photosystem for photons.  相似文献   

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