Density and birefringence of a highly stable α,α,β-trisnaphthylbenzene glass

Spectroscopic ellipsometry has been used to understand the properties of α,α,β-trisnaphthylbenzene (ααβ-TNB) glasses vapor-deposited at a substrate temperature of 295 K (0.85 T(g)). In a single temperature ramping experiment, a range of properties of the as-deposited glass can be measured, including density, fictive temperature, onset temperature, thermal expansion coefficient, and birefringence. The vapor-deposited ααβ-TNB glass is 1.3% more dense than the ordinary glass prepared by cooling at 1 K/min, is found to be birefringent, has a fictive temperature 35 K below that of the ordinary glass, and an onset temperature 20 K above that of the ordinary glass. The thermal expansion coefficient of the vapor-deposited ααβ-TNB glass is 14% lower than that of the ordinary glass, indicating that lower portions of the potential energy landscape have more harmonic potential minima than the parts accessible to the ordinary glass.     

铁合金厂回收的硅微粉在不同温度下晶相结构的研究

铁合金厂冶炼过程产生的大量硅微粉烟尘, 可以作为耐火材料和窑具材料的结合剂, 活性剂和矿化剂, 可促进耐火材料固相反应和烧结, 有利于晶型的转变, 提高耐火材料的高温性能。硅微粉在高于或等于1100 ℃不析晶。1200和1300 ℃析晶规律是:首先α-石英转变为α-方石英, 然后转变为α-鳞石英。在1400～1450 ℃首先析出卡片号为290085的石英变体, 然后转变为α-方石英。 而常规转化过程是α-方石英很难形成α-鳞石英, 而且不形成290085的变体, 因此其转化规律与常规不同。在液相存在情况下, 少量α-方石英转变为α-鳞石英, 不同温度下析晶结构探讨为实际生产提供适宜的升温曲线。     

鲁米诺在铂热控微电极上的电致化学发光行为研究

研究了鲁米诺在铂热控微电极上的电致化学发光(ECL)行为。当电极表面温度为25℃时,在0.80 V有一个明显的ECL峰(ECL-2);当电极表面温度高于43℃时,鲁米诺在0.45 V和0.80 V各出现一个ECL峰(ECL-1和ECL-2),而且这两个峰的强度随着电极表面温度的变化而变化。同时,对各ECL信号的发光机理进行了探讨。     

One-electron oxidized nickel(II)-(disalicylidene)diamine complex: temperature-dependent tautomerism between Ni(III)-phenolate and Ni(II)-phenoxyl radical states

The one-electron oxidized species of a Ni(II)-phenolate complex has been shown to be in the Ni(II)-phenoxyl radical state at room temperature and the Ni(III)-phenolate state at < -120 degrees C, indicating that the oxidation state is temperature dependent.     

A non-ionic surfactant as a new solvent for liquid-liquid extraction of zinc(II) with 1-(2-pyridylazo)-2-naphthol

A new method for extracting zinc(II) with 1-(2-pyridylazo)-2-naphthol (PAN) has been developed, based on the fact that a micellar solution of a non-ionic surfactant separates into two phases above a certain temperature, defined as the cloud point. Polyoxyethylene nonyl phenyl ether, (PONPE-7.5; average number of ethylene oxide units 7.5) was used as the surfactant. The cloud point of a 0.40% PONPE-7.5 solution is 1 degrees , and hence the solution is turbid at room temperature. The two phases can be separated by centrifuging for 8 min at room temperature. The zinc chelate of PAN is quantitatively extracted from 50g of the solution into a small volume (about 1 ml) of the lower (surfactant-rich) phase over the pH range 8.0-11.5. After most of the supernatant solution has been removed, the amount of final solution is adjusted to 2.00 g with 0.5 g of 10% of PONPE-20 solution and water. This mixture is transparent at room temperature. The absorbance is measured as 535 nm. Concentration factors of up to 25 can be obtained by choosing appropriate amounts of final ( 2.0 g) and initial solution ( 50 g). This new technique has been applied to the determination of zinc(II) in tap water.     

耐压多样品微量衍生反应装置在气相色谱-质谱联用法分析极性杂环胺中的应用

设计并制作了耐压多样品微量衍生反应装置。在该装置中采用N-(叔丁基二甲基硅烷基)-N-甲基三氟乙酰胺(MTBSTFA,含1%叔丁基二甲基氯硅烷)硅烷化试剂高温衍生极性杂环胺,衍生产物可以直接在气相色谱-质谱联用仪上分析。使用该装置,既可以在比试剂沸点高的温度下实现衍生反应,也可以实现多个微量样品的同时衍生。着重考察了衍生化过程中反应瓶的顶空体积、试剂蒸发面积、温度、时间等实验条件的影响。结果表明,在90 ℃衍生时,与普通衍生装置相比,使用耐压衍生装置可以有效地减小挥发损失,显著增大衍生产量;在150 ℃衍生时,由于试剂挥发损失严重导致普通衍生装置无法使用,而采用耐压衍生装置却可以实现定量衍生,但通过加温加压方式来加快衍生反应速率的效果并不十分明显。     

Temperature effects in the environmental stress cracking of polyethylene

An already existing model describing three types of behavior in the environmental stress cracking (ESC) of polyethylene (PE) subjected to uniaxial tensile loading at 25°C has been extended to cover the temperature range 25-50°C. Three effects have been observed and are found to be qualitatively consistent with the model. The transition between “pure” ESC (zone 1) and liquid-flow-controlled behavior (zone 2) occurs at shorter times for higher temperatures—an effect mainly due to reduced liquid viscosity. “Pure” ESC is less temperature dependent than failure occurring without the liquid playing a significant role (zone 3). This has been attributed to a compensation of reduced mechanical resistance of the polymer at higher temperatures, by reduced stress concentrations at the crack tip due to local absorption of the liquid. The transition time between zones 2 and 3 increases with temperature. Although it is surprising at first sight, this effect is shown to be compatible with the ESC model.     

Random binary brush architecture enhances both ionic conductivity and mechanical strength at room temperature

The ionic conductivity and the mechanical strength are two key factors for the performance ofpoly(ethylene oxide) (PEO) based polyelectrolytes.However,crystallized PEO suppresses ion conductivity at low temperature and melted PEO has low mechanical strength at high temperature.Here,random binary brush copolymer composed of PEO-and polystyrene (PS)-based side chains is synthesized.PEO crystallinity is suppressed by the introduction of PS brushes.Doping with lithium trifluoromethanesulfonate (LiTf) induces microphase separation.Due to a random arrangement of the brushes,the microphase segregation is incomplete even at high salt loading,which provides both high ionic conductivity and high mechanical strength at room temperature.These results provide opportunities for the design of polymeric electrolytes to be used at room temperature.     

A highly sensitive and nonradioactive mutation detection method based on vertical gradient temperature single-strand conformation polymorphism.

The single-strand conformation polymorphism (SSCP) method is widely used for mutation detection. The sensitivity of the method depends on several factors, most importantly on the temperature at which electrophoresis of single-stranded DNA (ssDNA) takes place. The temperature has a profound effect on the folded conformation of ssDNA. The temperature factor is predominantly determined empirically in conventional SSCP, which can be very tedious especially when a large number of different DNA samples need to be screened. We have devised a novel SSCP method based on a vertical gradient temperature (VGT), which automatically subjects ssDNA to various temperatures in the same electrophoresis. The theory behind VGT-SSCP protocol is that when ssDNA is subjected to run in a wide range of gradient temperature, it will automatically acquire optimal resolution at an optimal temperature to distinguish between the wild type and the mutant type ssDNA. The sensitivity level of mutation detection of VGT-SSCP depends on whether the corresponding optimal secondary structure of a mutant DNA strand is within the preset gradient temperature range. In summary, the VGT-SSCP is a simple and robust nonradioactive method that is more sensitive than constant-temperature SSCP in detecting unknown mutations.     

二氧化硅-聚-γ-巯丙基硅氧烷-铂络合物对不饱和化合物的硅氢加成的催化活性和稳定性

<正> 文献指出带有二苯膦、二甲基胺或氰基基团的聚苯乙烯、聚烯丙基氯和聚甲基丙烯酸酯的铂或铑的络合物可用来作为烯烃的非均相硅氢加成催化剂。我们曾经发现二氧化硅-聚-γ-氨丙基硅氧烷-铂络合物(简称为Si-NH_2-Pt)也是一种对烯烃的硅氢加成具有高活性及选择性的催化剂。     

Temperature variation effects on the determination of acidity constants through the internal standard–capillary electrophoresis method

The internal standard (IS) CE (IS‐CE) method is an interesting alternative to other methods for the determination of acidity constants of compounds. Although some of the advantages of this method have been already reported, the method has not been tested yet as regards to temperature effects. This has been the aim of this work, where it is demonstrated that the method can be applied successfully for the determination of pK_as at different temperatures, if the acidity constant of the IS at the desired temperature is known. The fact of obtaining the acidity constants at different temperatures allows the calculation of some thermodynamic quantities, such as the molar standard enthalpy and the molar standard entropy in a fast way. It is also demonstrated that if the IS and the test compound have similar standard enthalpy increment, the IS compensates uncontrolled possible temperature fluctuations (e.g., due to Joule heat) inside the capillary obtaining reliable acidity constant values at the desired temperature.     

Experimental evidence for a temperature dependent transition between normal and inverse equilibrium isotope effects for oxidative addition of H2 to Ir(PMe2Ph)2(CO)Cl

The equilibrium isotope effect (EIE) for oxidative addition of H(2) and D(2) to Ir(PMe(2)Ph)(2)(CO)Cl has been measured over a large temperature range, thereby demonstrating that the inverse (<1) EIE previously observed at ambient temperature becomes normal (>1) at high temperature (>90 degrees C). The temperature dependence of the EIE for oxidative addition of H(2) and D(2) to Ir(PH(3))(2)(CO)Cl has been calculated using the geometry and vibrational frequencies obtained from DFT (B3LYP) calculations on Ir(PH(3))(2)(CO)ClH(2) and Ir(PH(3))(2)(CO)ClD(2), and is in accord with the experimentally observed transition from an inverse to normal EIE for oxidative addition of H(2) and D(2) to Ir(PMe(2)Ph)(2)(CO)Cl: the EIE is calculated to be inverse between 0 and 510 K, reach a maximum value of 1.15 at 867 K and then slowly decrease to unity as the temperature approaches infinity. This deviation from simple van't Hoff behavior, and the occurrence of a maximum in the EIE, is the result of the entropy term being temperature dependent. At low temperature, the enthalpy term dominates and the EIE is inverse, whereas at high temperatures the entropy term dominates and the EIE is normal. The observation of both normal and inverse EIEs for the same system indicate that inferences pertaining to the magnitude of an isotope effect at a single temperature may require more detailed consideration than previously realized.     

Structure study and luminescence thermochromism in hexanuclear 6-methyl-2-pyridinethiolato copper(I) crystals

The structure of hexanuclear 6-methyl-2-pyridinethiolato copper(I) [Cu6(6-mpyt)(6)] crystals has been studied by the X-ray diffraction analysis. These crystals show highly efficient luminescence whose color changes drastically from red to green-blue with lowering temperature from room temperature (RT) to liquid nitrogen temperature (LNT). This is a new example of luminescence thermochromism for hexanuclear copper(I) cluster compounds. Two relaxed luminescence bands appear predominantly: one (CC-band), red luminescence appearing in the lower-energy region around 1.8 eV at higher temperature, is assigned to the transition between intramolecular orbitals (MO) of a Cu cluster center (CC), and the other (CT-band), green-blue luminescence appearing at the higher energy side of 2.6 eV than the CC-band at lower temperature, is assigned to a charge transfer (CT) transition from the CC-MO to a ligand MO. Additionally, the CT band can be deconvoluted to two subbands CT(L) and CT(H). The intensities of the CC- and the CT-bands change complementarily with temperature via a thermal activation process, giving the thermochromism. All of these band shapes can be fitted by a Gaussian function, and their widths are fairly large obeying the hyperbolic cotangent law. These features reflect our system to be a strong electron-lattice coupling one. The relaxation process of the photoexcited states is discussed in terms of a configuration coordinate model.     

Metal-directed synthesis and photophysical studies of trinuclear v-shaped and pentanuclear x-shaped ruthenium and osmium metallorods and metallostars based upon 4'-(3,5-dihydroxyphenyl)-2,2':6',2''-terpyridine divergent units

A new series of V-shaped trinuclear metallorods and X-shaped pentanuclear metallostars has been prepared by the reaction of metal complexes bearing pendant phenolic functionalities with complexes containing electrophilic ligands. Specifically, {M(tpy)2} motifs (M=Ru or Os; tpy=2,2':6',2'-terpyridine) bearing one or two pendant 3,5-dihydroxyphenyl substituents at the 4-position of the central ring of the tpy have been reacted with the complexes [Ru(tpy)(Xtpy)]2+ (X=Cl or Br) to form new ether-linked species. The energy transfer from ruthenium to osmium in these complexes has been investigated in detail and the efficiency of transfer shown to be highly temperature dependent; the energy transfer is highly efficient at low temperature, whereas at room temperature nonradiative and nontransfer deactivation of the excited {Ru(tpy)2}* domains is most significant.     

Temperature induced restoration of fluorescence from oxidised single-walled carbon nanotubes in aqueous sodium dodecylsulfate solution

Fluorescence intensity from single walled carbon nanotubes in aqueous sodium dodecylsulfate solution is shown to be strongly temperature dependent in the range 5-60 degrees C. Emission peaks corresponding to particular nanotube species which have been quenched due to oxidation by aerated water show sharp transitions at distinct temperatures as the sample is heated. The temperature at which the transition occurs is found to be species dependent and has been interpreted as being proportional to the valence band edge potential of the nanotube. The results are explained quantitatively using the Nernst equation to measure the increase in reduction potential of the solution as the temperature is raised. The removal of dissolved O(2) and CO(2) is thought to be a significant driving force in the reversal of the redox reaction which causes oxidation of the nanotubes.     

Clouding phenomenon and SANS studies on tetra-n-butylammonium dodecylsulfate micellar solutions in the absence and presence of salts

Clouding phenomenon in aqueous micellar solutions of an anionic surfactant tetra-n-butylammonium dodecylsulfate (TBADS) has been observed as a function of surfactant concentration. Small-angle neutron scattering (SANS) experiments in these systems show clustering of micelles as the temperature approaches the cloud point (CP). The individual micelles and the clusters of micelles coexist at CP. The clustering of micelles depends on the surfactant concentration and temperature. It is proposed that clustering is due to depletion of H-bonded water present around the butyl chains at the micellar surface. This is associated with entropy gain which is considered to be the major thermodynamic factor related to micellar aggregation. The structures (clusters) that emerge depend on the relative lengths of the alkyl chains of the counterion and can be tuned by the temperature.     

Low-temperature reaction of trialkoxysilanes on silica gel: a mild and controlled method for modifying silica surfaces

The room temperature reaction of 4-(triethoxysilyl)butyronitrile, 4-TBN ((C2H5O)3Si(CH2)3CN), on weakly hydrated silica samples pretreated at 393 K has been studied by desorption experiments and by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy at different aging times under various water partial pressures. The reaction is demonstrated by the decrease of desorption of 4-TBN with time and the simultaneous disappearance of the 2980 and 1394 cm(-1) signals in the DRIFT spectra, assigned to the CH3 moiety of the ethoxy functions. Water partial pressure is shown to have a crucial effect on the rate and efficiency of the process as, after 6 days, for samples kept at room temperature under vacuum, ca. 50% of the silane has reacted, while for those kept in a water-saturated atmosphere the silane reaction reaches 96%. Although the silane appears to be irreversibly bonded to the surface, no definite conclusion may be drawn from these preliminary results as to the nature of the bonding (grafting or coating). These samples are compared to modified silicas prepared according to conventional methods. The same extent of silane reaction (50%) is achieved for preadsorbed samples kept under vacuum and either cured at 473 K for 30 h or kept at room temperature for 6 days. A mild and controlled modification of silica by triethoxysilanes can thus be achieved by first physisorbing known amounts of the modifying silanes from an organic solvent on pretreated silica and then letting the samples mature for a few days at room temperature in a water-saturated atmosphere.     

Benzhydryl as an efficient selective nitrogen protecting group for uracils

Regioselective N-substitution of the less active nitrogen within uracil analogues has been achieved following preliminary N-protection at the more active N-position with a benzhydryl protecting group. This protecting group is stable to concentrated HCl (aqueous) at reflux temperature, TFA at room temperature, and Pd-C-catalyzed normal pressure hydrogenation at room temperature; the benzhydryl group can be removed quantitatively and selectively with a 10% triflic acid solution in TFA at 0 degree C.     

Moisture sorption in polyamide 6.6: Experimental investigation and comparison to four physical-based models

Water sorption in polyamide 6.6 has been characterized for a wide range of temperature (25°C to 80°C) and various water activities using a Dynamic Vapor Sorption testing machine. Complex sorption mechanisms govern the water uptake in the material. The competition between two main temperature dependant mechanisms has been observed: a Henry's sorption mechanism that mainly governs the sorption curve at low water activities, and a second mechanism at high water activities that could be related to the formation of water clusters. It is observed that the temperature dependency can mainly be attributed to the Henry's contribution. Four physically based models are then used and identified thanks to the extended experimental database. It is shown that a simple Flory-Huggins model is not able to capture the experimental observations at very high water activities for all the temperatures tested. The ENSIC model is a better choice, but good prediction for very high water activity cannot be obtained. Both modified Park and GAB models can accurately predict the volume fraction of water for the whole ranges of water activity and temperature, although the modified Park model should be preferred considering the number of parameters and the mathematical simplicity.     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物的微相分离与结晶

本工作研究了多分散和单分散聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物(PEO-PS-PEO)的结晶行为,及这些试样按非晶型嵌段共聚物进行微相分离后再结晶的结晶特点.