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1.
Complementary techniques had to be applied to investigate the binary system tetradecanedioic acid (C14H26O4)–hexadecanedioic acid (C16H30O4), because all the forms observed have the same space group (P21/c; Z = 2). We studied the polymorphism of the two single compounds and of their mixtures by X‐ray powder diffraction, differential‐scanning calorimetry (DSC), infrared spectroscopy (IR), scanning electron microscopy (SEM), and thermo‐optical microscopy (TOM). The two diacids were found to be isopolymorphic. At low temperature, they crystallize in the same ordered C‐form, and, on heating, adopt the ordered Ch‐form, 1° below their melting point. In contrast to similar compounds (unbranched alkanes, alkanols, and fatty acids), the solid–solid and solid–liquid phase‐transition temperatures decrease with increasing chain length. At low temperature, a new monoclinic form, Ci, appears as a result of the disorder of composition in the mixed samples. There are two [C + Ci]‐type solid–solid domains. On heating, the solid domains are related to solid–liquid domains by a peritectic invariant for compositions rich in C14H26O4, and by a eutectic invariant for compositions rich in C16H30O4. At higher temperature, there appears a second peritectic invariant for compositions rich in C14H26O4, together with a metatectic invariant for compositions rich in C16H30O4. All the solid forms observed in this binary system are isostructural. Nevertheless, the equilibrium between them is complex near the melting point, and their miscibility in the solid state is reduced.  相似文献   

2.
A one-dimensional porous electrode (PE) model and additional consideration of the dependence of the local solution conductivity on its gas saturation was used to study the effect of simultaneous hydrogen evolution on distribution of the potential in PE and the overall rate of the target redox reaction. It was found that this effect depends on the ratio of conductivities of the solid κs and liquid κl phases and direction of solution supply and can be both negative (rear supply at any κs and κl, front supply at κs ≫ κl), and positive (front supply at κs ≤ κl). However, variation of the target reaction rate in all cases for PE with a high specific surface area is low (10–40%). It is shown that in the terms of the model of a homogeneous gas-liquid mixture, a weak effect of gaseous hydrogen is related to the specific form of profiles κl(x) far from the earlier considered ideal (or inverse) liquid-phase conductivity profiles.  相似文献   

3.
Melting is a most familiar phenomenon: closely similar patterns of solid/liquid transformation occur on heating innumerable and diverse crystalline substances. While some behaviual trends have been characterized, no melting theory of general applicability has yet found widespread acceptance. The present comparative survey is concerned with the melting of metallic elements, to determine quantitatively the enthalpy and density changes that accompany these solid/liquid transitions. The relationship of melting with other physicochemical processes is considered. Metals were selected as apparently the simplest systems for this analysis, many crystal structures involve the close packing of (at least approximately) spherical atoms. Appropriate physical data are available for a large number of different elements, some 70 are considered here, representing a wide range of melting points, T m. Aspects of the kinetics and mechanisms of melting are discussed. These data comparisons show that melting enthalpies for metals are relatively small. The averages found represent only about 26% of the energy required to heat these solids from 0 K to completion of melting at Tm and only about 5% of the volatilization enthalpy. The density changes on fusion are also relatively small, on average -4.7%. To account for these observations, a representational model of fusion has been formulated. It is suggested that, on melting, the bonding and of local structural dispositions between neighbouring atoms in the liquid and in the solid condensed phases undergo changes that are only limited in extent. Thus, the regular ordered structures, characteristic of crystalline phases, are extensively maintained in the melt at Tm. Melting is ascribed to destabilization of the crystal through excess vibrational energy, resulting in replacement of the overall extended and constant rigid structure of the solid by a dynamic equilibrium between small, locally regular domains in the liquid. Each such structurally ordered domain is a region of one or other of the alternative possible, crystal-type structures of comparable stability. In the liquid, constant transfer of the components between these regular arrays, stabilised by the enthalpy of fusion, within the compact assemblage of domains accounts for the fluidity of the liquid, its inability to withstand a shearing force and the absence of long-range order. Melting is, therefore, identified with relaxation, at T m, of the constraint that only a single lattice form is present (as in a crystal) and the liquid is composed of all the structures that are sufficiently stable to participate in the constant flux of interconverting domains. This model of melting may have wider applicability. The small modifications both of enthalpy and of density on fusion make the formulation of a quantitative model, capable of predicting T m, difficult because minor or secondary controls may be significant in determining the temperature of this physical phase change and the structural changes that occur.  相似文献   

4.
Abstract

The particular phase in which a liquid crystal system will exist is that which has the lowest free energy at a certain temperature. The free energy may depend on variables such as temperature, pressure, chirality, etc. One way in which the stability of a particular thermodynamic phase, relative to its neighbours, would be manifest is in its temperature range. The effect of chirality, in particular, on the temperature range or stability of blue phases has been well-studied both experimentally and theoretically. To date these studies assume that chirality is the only parameter which will influence the existence of blue phases. However, blue phases with relatively low chirality and broad range, which should in principle only show very narrow blue phases, have been reported. This suggests that factors other than chirality are involved in blue phase stability. In this paper we investigate the phase stability of various blue phase mixtures containing equal amounts of a chiral dopant, via their blue phase temperature range. Correlation between blue phase stability and the elastic constants k 2 and k 22, molecular length of the nematic host, and the order parameter at the blue phase to cholesteric transition is discussed. We have confirmed that for our mixtures the total blue phase temperature range may be related equally to the elastic constant k 22 and the chirality. We also present the first data displaying an odd-even effect in blue phases. Finally, we have found an apparent correlation between the stability of the blue phases and the magnitude of the orientational order parameter of the cholesteric phase at the cholesteric to blue phase transition.  相似文献   

5.
The architecture of the plasma membrane is not only determined by the lipid and protein composition, but is also influenced by its attachment to the underlying cytoskeleton. Herein, we show that microscopic phase separation of “raft‐like” lipid mixtures in pore‐spanning bilayers is strongly determined by the underlying highly ordered porous substrate. In detail, lipid membranes composed of DOPC/sphingomyelin/cholesterol/Gb3 were prepared on ordered pore arrays in silicon with pore diameters of 0.8, 1.2 and 2 μm, respectively, by spreading and fusion of giant unilamellar vesicles. The upper part of the silicon substrate was first coated with gold and then functionalized with a thiol‐bearing cholesterol derivative rendering the surface hydrophobic, which is prerequisite for membrane formation. Confocal laser scanning fluorescence microscopy was used to investigate the phase behavior of the obtained pore‐spanning membranes. Coexisting liquid‐ordered‐ (lo) and liquid‐disordered (ld) domains were visualized for DOPC/sphingomyelin/cholesterol/Gb3 (40:35:20:5) membranes. The size of the lo‐phase domains was strongly affected by the underlying pore size of the silicon substrate and could be controlled by temperature, and the cholesterol content in the membrane, which was modulated by the addition of methyl‐β‐cyclodextrin. Binding of Shiga toxin B‐pentamers to the Gb3‐doped membranes increased the lo‐phase considerably and even induced lo‐phase domains in non‐phase separated bilayers composed of DOPC/sphingomyelin/cholesterol/Gb3 (65:10:20:5).  相似文献   

6.
The morphological development and crystallization behavior of a poly(ethylene terephthalate)/poly(hydroxyl ether of bisphenol A) (phenoxy) blend were studied with time‐resolved light scattering, optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering (SAXS). During annealing at 280 °C, liquid–liquid phase separation via spinodal decomposition proceeded in the melt‐extruded specimen. After the formation of a domain structure, the blend slowly underwent phase homogenization by the interchange reactions between the two polymers. Specimens annealed for various times (ts) at 280 °C were subjected to a temperature drop and the effects of liquid‐phase changes on crystallization were then investigated. The shifts in the position of the cold‐crystallization peaks indicated that the crystallization rate is associated with the composition change of the separated phases as well as the change of the sequence distribution in polymer chains during annealing. The morphological parameters at the lamellar level were determined by a correlation function analysis on the SAXS data. The crystal thickness (lc) increased with ts, whereas the amorphous layer thickness (la) showed little dependence on ts. Observation of a constant la value revealed that a large number of noncrystallizable species formed by the interchange reactions between the two polymers were excluded from the lamellar stacks and resided in the interfibrillar regions, interspherulitic regions, or both. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 223–232, 2008  相似文献   

7.
The absolute rate constants for the intermolecular hydrogen abstraction reactions of secondary hydrogens by secondary alkylperoxy radicals in hexadecane autoxidation, k3, have been determined in the temperature range of 120–190°C using the stirred flow reactor technique. Absolute rate constants determined in this study for hexadecane are in good agreement with those determined for other hydrocarbons in liquid phase, on a per hydrogen basis, at lower temperatures. Arrhenius parameters for k3/H derived from this study are A = 108.6 M?1 s?1 and Ea = 16.0 kcal/mol. The values of these parameters provide experimental confirmation for previous estimates made from both lower temperature reactions in the liquid phase and higher temperature reactions in the gas phase. © 1994 John Wiley & Sons, Inc.  相似文献   

8.
s-Butoxy radicals have been generated by reacting fluorine with s-butanol: Over the temperature range 398.6 to 493.3 K the s-butoxy radical decomposes by two different pathways to yield acetaldehyde and propionaldehyde, acetaldehyde being the major product: The ratio k1/k2 was found to be temperature dependent. An Arrhenius plot of the data (398.6 to 493.3 K) yields the relative Arrhenius parameters, E1 - E2 = ?11.2 ± 0.8 kJ mol?1 and (A1/A2) = 0.59 ± 0.14. The ratio of rate constants k1/k2 was shown to be independent of total pressure (80–600 torr) and of the pressure of s-butanol (2–13 torr). The kinetic results for these s-butoxy decomposition reactions are discussed in relation to the literature data and in terms of the thermochemistry of the reactions.  相似文献   

9.
The results of studies concerning two- and three-phase systems in an agitated vessel are presented. The aim of our research was to investigate the effect of the physical properties of the liquid phase on the value of the volumetric gas-liquid mass transfer coefficient in mechanically agitated gas-liquid and gas-solid-liquid systems. Our experimental studies were conducted in a vessel with an internal diameter of 0.288 m. The flat bottom vessel, equipped with four baffles, was filled with liquid up to a height equal to the inner diameter. The liquid volume was 0.02 m3. Three high-speed impellers of a diameter equal to 0.33 of the vessel diameter were used: Rushton turbine (RT), Smith turbine (CD 6), or A 315 impeller. The measurements were carried out in coalescing and non-coalescing systems. Distilled water and aqueous solutions of an electrolyte (sodium chloride) of two different concentrations were used as the liquid phase. The gas phase was air. In the three-phase system, particles of sea sand were used as solid phase. The measurements were conducted at five different gas-flow rates and three particle loadings. Volumetric gas-liquid mass transfer coefficients were measured using the dynamic method. The presence and concentration of an electrolyte strongly affected the value of the gas-liquid mass transfer coefficient in both two- and three-phase systems. For all agitators used, significantly higher k l a coefficient values were obtained in the 0.4 kmol m−3 and 0.8 kmol m−3 aqueous NaCl solutions compared with the data for a coalescing system (with distilled water as the liquid phase). The k l a coefficient did not exhibit a linear relationship with the electrolyte concentration. An increase in the sodium chloride concentration from 0.4 kmol m−3 to 0.8 kmol m−3 caused a considerable decrease in the volumetric mass transfer coefficient in both the two-phase and three-phase systems. It was concluded that the mass transfer processes improved at a certain concentration of ions; however, above this concentration no further increase in k l a could be achieved.  相似文献   

10.
A thermophysical study of the sulfur containing amino acids l-cysteine and l-cystine has been carried out by differential scanning calorimetry (DSC). Heat capacities of both compounds were measured in the temperature interval from T = 268 K to near their respective melting temperatures. DSC and variable temperature powder X-ray diffraction analysis (PXRD) gave evidence for a solid–solid phase transition close to the melting point only in the l-cysteine sample. DSC experiments show that this solid–solid transition is not reversible in the temperature interval T = 235–485 K and presents a behavior depending on heating temperature, time, and rate. This behavior is also supported by variable-temperature PXRD. The patterns for the commercial samples, at room temperature, are consistent with those simulated for the orthorhombic and hexagonal polymorphic forms from the single-crystal X-ray analysis.  相似文献   

11.
Quan Bai  Xindu Geng 《Chromatographia》2001,54(5-6):335-338
Summary Based on a stoichiometric displacement model for retention (SDM-R) in liquid chromatography, the two linear plots, log/(a constant relating to the affinity of one mole of solute to the stationary phase) andZ (the total moles of the displacing agent released at the interface between stationary phase and solute molecules as one mole of the solute is absorbed by the stationary phase) of small solutes and biopolymers versus the reciprocal of absolute temperature, l/T, in reversed-phase liquid chromatography were theoretically derived and experimentally proved to be linear and to have a common point called the temperature convergent point. The two linear plots could be used instead of the plot of logk to l/T which is normally only valid for small solutes but not for biopolymers for investigations of chromatographic thermodynamics and temperature convergence. The average convergence temperature (T conv) of biopolymers was theoretically derived to equal the ratio between the slope and the intercept from either one of the two linear plots and to be 130.8±9.3°C for five proteins which are very close to those of biopolymers by calorimetry. A new methodology to investigate chromatographic thermodynamics and possibly for investigating the temperature convergence of biopolymers in the process of protein folding is also presented.  相似文献   

12.
A series of N-alkyl-N-alkyl′-pyrrolidinium-bis(trifluoromethanesulfonyl) imide (TFSI) room temperature ionic liquids (RTILs) has been investigated by means of thermogravimetric analysis (TG), differential scanning calorimetry, FT-IR spectroscopy, and X-ray diffraction analysis. These compounds exhibit a thermal stability up to 548–573 K. The mass loss starting temperature, T ml, falls in a narrow range of temperatures: 578–594 K. FT-IR spectra, performed before and after 24 h isothermal experiments at 553 and 573 K, have confirmed their great thermal stability. Below the ambient temperature, these compounds exhibit a complex behavior. N-methyl-N-propyl-pyrrolidinium-TFSI is the sole liquid which crystallizes without forming any amorphous phase even after quenching in liquid nitrogen. Its crystalline phase has a melting point, T m, of 283 ± 1 K. When the amorphous solid is heated, the N-butyl-N-ethyl-pyrrolidinium-TFSI presents a glass transition temperature, T g, at 186 K followed by a cold crystallization, T cc, at 225 K, and a final T m at 262 K. The N-butyl-N-methyl-pyrrolidinium-TFSI exhibits a T g between 186 and 181 K, its cold crystallization leading to two different solid phases. Solid phase I has a melting point T I,m = 252 K and phase II, T II,m = 262 K. When the amorphous phase is obtained at a cooling rate of 10 K/min, its T cc is 204 K, and a metastable solid phase (III) is obtained which transforms into the phase II at 226 K. However, when the sample is quenched, the amorphous phase transforms into phase II at T cc = 217 K and phase I at 239 K. P15-TFSI exhibits the most complicated pattern as, on cooling, it leads to both a crystallized phase at 237 K and an amorphous phase at 191 K. On heating, after a T g at 186 K and a T cc at 217 K, two solid–solid phase transitions are observed at 239 K and 270 K, the final T m being 279 K.  相似文献   

13.
This paper reports on the enantioseparation of racemic phenylalanine or D-phenylalanine and Lphenylalanine via a hollow fibre-supported liquid membrane (HFSLM) and the results are compared with the mathematical model. The enantioseparation results, of 80 % and 73 %, showed the highest extraction and stripping of l-phenylalanine from the feed phase and the enantiomeric excess (% ee) of 60 % from 6 mmol L?1 of initial rac-phenylalanine in the feed solution. The optimum parameters were feed solution at pH 5, 6 mmol LL?1 of O,O′-dibenzoyl-(2S,3S)-tartaric acid ((+)-DBTA) as the extractant in octanol as the liquid membrane, and deionised water as the stripping solution. Equal flow-rates of feed and stripping solutions of 100 mL minL?1 were adjusted in a batch operation mode for 50 min at ambient temperature. From the calculation, the equilibrium constants of extraction (K ex) and mass transfer coefficients in the feed phase (k f) and in the liquid membrane phase (k m) were found to be 1.81 L mmol?2, 3.50 × 10?2 cm s?1, and 1.40 × 10?2 cm s?1, respectively. Finally, the change in concentrations of d,l-phenylalanine over time in the feed and stripping solutions by mathematical model were estimated and compared with the experimental results. The values thus calculated were in agreement with the experimental data with the average deviation of approximately 3 %.  相似文献   

14.
Abstract

Ultrasonic sound velocities and densities were measured for the binary mixtures of p-chlorotoluene with l-alcohols. The alcohols included: l-propanol, l-butanol, l-pentanol, l-hexanol and l-heptanol. Isentropic compressibilities, ks and deviation in isentropic compressibility, Ks from ideal behaviour have been calculated from the results. The deviation in isentropic compressibility has been ascribed to competition between structure-breaking and structural effects to different extents.  相似文献   

15.
Abstract

The connexion between the equation of state of a classical fluid of non-polarizable ions, the character of the screening, and the appearance of long range oscillations in the chargetharge radial distribution function is examined. While considerations of stability lead to the usual inequalities for the inverse static dielectric function and the compressibility of the charged fluid, the square of the inverse screening length k 3, does not need to be positive for thermodynamic stability. Through a study of an approximate equation of state for a twocomponent fluid of charged hard spheres, the regions of negative and positive k 2 in the pressuredensity plane are related to a liquid phase and to an ionized-gas phase, respectively. The model fluid displays a gas-liquid critical point, above which the transition between the two types of screening is continuous. This behaviour of the charged-hard-spheres fluid is contrasted with the transition of a real ionic liquid to the molecular gaseous phase.  相似文献   

16.
The melting curve of NH4HF2 I rises from 125.2°C at atmospheric pressure to a triple point II/I/liquid at 9.3 kbar, 220°C. The I/II phase boundary is terminated at a triple point III/I/II at ∼45 kbar, 295°C. The melting curve of the new phase NH4HF2 II passes through a broad maximum at ∼39 kbar, 306°C, and is terminated at a triple point III/II/liquid at 46.3 kbar, 301°C. The melting curve of NH4HF2 III rises with pressure. The NH4HF2 III may be a dense hydrogen-bonded phase. Liquid NH4HF2 appears to be anomalous in several respects, and has a high compressibility relative to the solid phases.  相似文献   

17.
Two kinds of ionic self‐assembled complexes of linear or branched poly(ethyleneimine) (lPEI or bPEI) with Percec‐type dendrons [(3,4,5)16G1‐COOH] were prepared as lPEI‐(3,4,5)16G1‐x and bPEI‐(3,4,5)16G1‐x , where x is the mole ratio of the carboxyl groups of the dendritic amphiphile to the amino groups at the PEI chain. The crystal and mesomorphous structures and thermal properties of these complexes were investigated with X‐ray diffraction (XRD), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), and polarized optical microscope (POM). Both the lPEI and bPEI complexes exhibited the same αH crystal phase and similar lamellar mesomorphous phase, irrespective of the branching of the polymer backbone and the binding degree. The lPEI series complexes lPEI‐(3,4,5)16G1‐x , however, had more ordered lamellar stacking than that of the bPEI‐(3,4,5)16G1‐x complexes, so the thermotropic liquid crystal phase SmA was formed only in the lPEI‐(3,4,5)16G1‐x complexes beyond the melting point of the tail crystal of the dendritic amphiphile. No liquid crystalline phase was found from the bPEI‐(3,4,5)16G1‐x complexes. The results suggest that the branching of polymer backbone plays a key role to the formation of thermotropic liquid crystal in the polymer–dendritic amphiphile complex. The present finding is significant for the design of functional nanostructures based on the ionic complexation of polymers and amphiphiles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011  相似文献   

18.
Three aldohexose monosaccharides, d-glucose, d-mannose, and d-galactose, were examined by scanning temperature dielectric analysis (DEA) from ambient temperatures through their melts. Phase transitions, including glass transition (T g) and melting temperature (T m), were evaluated by differential scanning calorimetry (DSC). The monosaccharides were found to exhibit thermally-induced dielectric loss spectra in their amorphous-solid phase before melting. Activation energies for electrical charging of each of the monosaccharides were calculated from an Arrhenius plot of the tan delta (e″/e′, dielectric loss factor/relative permittivity) peak frequency versus reciprocal temperature in Kelvin. The DEA profiles were also correlated with the DSC phase diagrams, showing the changes in electrical behavior associated with solid–solid and solid–liquid transitions.  相似文献   

19.
Laccase of Coriolus zonatus   总被引:1,自引:0,他引:1  
Laccase is one of the lignolytic enzymes found in liquid cultures of the fungus Coriolus zonatus in defined medium. The enzyme was isolated from culture liquid and characterized. Laccase from C. zonatus is a single-chain protein with a molecular mass of 60 kDa. Carbohydrate moiety of enzyme consisted of mannose, galactose and N-acetyl-glucosamine in a ratio of 6:2:0,6 respectively, and comprised 10% of the entiremolecule lsoelectric point was detected at pH 4.6. Laccase was found to have a pH optimum of 4.9 and temperature optimum of 55°C. Substrate specificity studies were conducted with catechol, K-ferrocyanide, hydroquinone, and sinapinic acid as substrates. The highest efficiency of catalysis was observed with sinapic acid as the substrate. The kinetic constants k cat and K28 of this reaction were 624 s−1 and 7 μM, respectively.  相似文献   

20.
We have studied the phase behavior of homologous series of diglycerol fatty acid esters (Qn‐D, for n=10, 12, 14, and 16, where n represents the carbon number in the alkyl chain length of amphiphile) in aqueous solution as a function of temperature and surfactant concentration. The different equilibrium phases present over a wide range of composition and temperature studied were characterized by means of visual observation under normal and polarized light, and x‐ray scattering techniques at small (SAXS) and wide angle (WAXS) regions. In diglycerol monocaprate (Q10‐D) and diglycerol monolaurate (Q12‐D)/H2O systems, lamellar liquid crystal (Lα) phase is present in the surfactant rich region and it swallows an appreciable amount of water. The amount of water swallowed by the Lα phase was determined by plotting the interlayer spacing, d, as a function of reciprocal of the surfactant weight fraction Ws . In the dilute regions, dispersion of Lα phase in water is observed over a wide range of temperature. At higher temperatures, the Lα phase melts to isotropic two‐liquid phases in water rich region whereas to isotropic reverse micellar solution (Om) in surfactant rich region. The Lα‐Om transition temperature is increased on increasing the hydrocarbon chain length of the surfactant from Q10‐D to Q12‐D. There is surfactant solid phase in equilibrium with water up to 25°C in diglycerol monomyristate (Q14‐D)/H2O system and the solid phase could solubilize 25 wt% water. The melting temperature of solid phase is practically constant in a wide range of compositions. Both the solid present region and the extent of water solubilization are increased in diglycerol monopalmitate (Q16‐D)/H2O system. At lower surfactant concentrations, excess water appears and dispersion of solid in water is formed. The structure of the solid is identified by WAXS measurement and it is confirmed to α‐solid. Normal vesicular aggregates are formed in Lα+W regions in the Q14‐D/H2O system at 25°C.  相似文献   

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