Melting behavior of poly(tetrahydrofuran)-S and their blends

Melting behavior of poly(tetrahydrofuran)-s (PTHF) and their blend with different molecular masses has been studied by TM-DSC. PTHF and their blend show two endothermic peaks on their curve. The melting peak temperatures T _m1 and T _m2, entropy of fusion ΔS _f1 and ΔS _f2, and mean relaxation time for melting τ_f1 and τ_f2 have been estimated, and their dependence on the molecular mass has been examined. Plots of Tm1 to the reciprocal of their molecular mass fit a simple equation (T _m=a-b/M _n). Plots of T _m2 to their molecular mass also fit the equation with different factors. There seems to be a boundary around molecular mass 1200 in the molecular mass dependence of ΔS _fand τ_f. Effect of blending appeared on the τ_f and the non-reversing heat flow. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of dyeing on melting behavior of poly(lactic acid) fabric

The effect of the dyeing on the melting behavior of poly(lactic acid) fabrics was investigated by differential scanning calorimeter. The DSC melting peaks at 10°C min^-1 of the untreated poly(lactic acid) fabric were observed at a temperature higher than those of the dyed fabrics. The restricting force from the extended tie molecules along the fiber axis seems to decrease in the dyeing process. When the sample was rapidly heated, the crystallites melted at lower temperatures since recrystallization was restricted. It was estimated, based on the heating-rate dependency of melting behavior, that the original crystallites of the untreated sample melted at 146.1°C and those of the dyed samples melted at higher temperatures, suggesting that their crystallites are grown to be more perfect in the dyeing process. This revised version was published online in July 2006 with corrections to the Cover Date.     

窄分子量分布聚四氢呋喃的合成

以发烟硫酸-高氯酸为催化剂,通过四氢呋喃的阳离子开环聚合合成了窄分子量分布的聚四氢呋喃(PTHF)。研究了发烟硫酸和高氯酸用量、反应时间、反应温度等对PTHF分子量(Mn)及其分布(Mw/Mn)的影响。结果表明,减少发烟硫酸或增加高氯酸用量可使Mn上升;反应时间超过3 h后,反应时间对Mn及Mw/Mn的影响不大;于2℃反应Mn有最大值(11 760);反应时间5 h,在N2中聚合的Mw/Mn较小;低转化率(Mw/Mn小于1.2)时,通N2对Mn(4 000~5 500)及Mw/Mn(1.12~1.19)的影响不大。     

Melting behavior of nylon 6 fiber in textiles

The melting process of constrained nylon 6 fibers has been studied to estimate the true melting point of its original crystals. The melting peak became simpler in shape and shifted to higher temperature with increasing fiber-axis restricting force. When heating rate, β, was increased, the temperature where the melting curve initially departs from its baseline, Tsm, decreased steeply in the range of 45 to 60°C min^-1, and increased linearly with increasing β above 60°C min^-1. By linear extrapolation of Tsm to 0°C min^-1, the temperature of ca 190°C was obtained for the melting temperature of the original nylon 6 crystals. This seems to correspond to the zero-entropy-production melting of the most imperfect crystallites of the nylon 6 fabric. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of sodium chloride on the melting temperature of collagen crystalline region in parchments

In order to observe the influence of sodium chloride on the melting temperature of collagen crystalline region in three new parchments, samples were soaked in water (blanks) and NaCl solutions of different concentrations, then removed, dried in air and measured by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The melting temperature of crystalline region of collagen, T _m, was determined as the minimum of the endothermal peak in the range 200–250 °C and as the inflection point of the decrease of storage modulus, respectively. There was observed a decrease in melting temperature of the salt-treated parchments compared to the samples soaked in water, sometimes significant (~20 °C) at certain concentrations of NaCl. Simultaneous TG/DTG/DSC thermal analysis (STA) was also applied for the determination of the amount of sodium chloride in salt-treated parchments, by calculating the mass loss due to the vaporization of NaCl, which occurs above 800 °C. By plotting T _m determined by DSC and DMA versus the NaCl content of the samples, an apparent minimum is observed. Additional information regarding the structural features was also obtained through X-ray diffraction (XRD) and attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR). XRD data put in evidence the preservation of collagen crystalline region in all salt-treated samples, while FTIR measurements did not showed significant modification of collagen. By removing the sodium chloride from the salt-treated parchments through washing with water, there is a return of the melting temperatures to the values of blank samples, demonstrating the reversibility of this phenomenon.     

The structure of the electric double layer: Atomistic versus continuum approaches

This article reviews recent forays in theoretical modeling of the double layer structure at electrode/electrolyte interfaces by current atomistic and continuum approaches. We will briefly discuss progress in both approaches and present a perspective on how to better describe the electric double layer by combining the unique advantages of each method. First-principles atomistic approaches provide the most detailed insights into the electronic and geometric structure of electrode/electrolyte interfaces. However, they are numerically too demanding to allow for a systematic investigation of the electric double layers over a wide range of electrochemical conditions. Yet, they can provide valuable input for continuum approaches that can capture the influence of the electrochemical environment on a larger length and time scale due to their numerical efficiency. However, continuum approaches rely on reliable input parameters. Conversely, continuum methods can provide a preselection of interface structures and conditions to be further studied on the atomistic level.     

Effect of temperature on the solubility of carnallite type double salts

A method based on Pitzer's model has been used for calculation of the solubilities of carnallite type double salts crystallizing in the systems MeX–MgX₂–H₂O (Me=Li, NH₄, K, Rb, Cs; X=Cl, Br). The solubility of congruently soluble double salts was also determined experimentally at 25–75°C. The results from studies of the solubility diagrams of ternary carnallite type water-salt systems over a wide temperature range are summarized. It is found that the width of the crystallization region for each of the salts can be explained by the relative differences in the solubilities of the ternary solution components (MeX, MgX₂·6H₂O and MeX·MgX₂·6H₂O) and by a change of temperature, and by the effect of temperature on the solubility. A method is proposed for calculating Pitzer's ternary parameters of interionic interaction (_MN and _MNX) on the basis of experimental data for the solubility in water of the double salts crystallizing in the corresponding ternary water-salt systems.     

Structure of dysprosium monotartrate in aqueous solution from magnetic double refraction and molecular mechanics data

pH-Metering and magnetic double refraction are used to determine the molar constant of magnetic double refraction of dysprosium monotartrate DyH₂L⁺ (H₄L is tartaric acid). A molecular mechanics technique (Dashevskii-Plyamovatyi model) was used to model the structure of the ligand and hydrate surroundings of dysprosium(III) in DyH₂L⁺. Theoretical molar constants of magnetic double refraction calculated from the molecular mechanics data (CONKERR program) were compared with the experimental values; the most probable models of the surroundings of the dysprosium(III) are established.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences, 420062 Kazan'. V. I. Ul'yanov-Lenin Kazan' State University, 420008 Kazan'. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2232–2237, October, 1992.     

Origin of double melting behavior of poly(p‐phenylene succinate)

The origin of double melting behavior of poly(p‐phenylene succinate) (PPSc) was investigated by differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction. As‐polymerized PPSc showed two melting peaks: the low melting (LM) and high melting (HM) peaks at 286 and 311 °C, respectively. When PPSc was annealed at 270 °C, the LM peak constantly shifted toward higher temperatures and grew in its area with annealing time, and eventually merged into the HM peak located at 308 °C. X‐ray diffractograms of PPSc annealed at 270 °C became sharper with increasing the annealing time while the peak positions did not change. The X‐ray diffractograms obtained from the LM and the HM peak exhibited the same diffraction peaks. It was concluded from these results that the double melting behavior of PPSc is due to the distribution of crystals having the same crystal form but differing in size and perfection. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1868–1871, 2000     

还原温度对双介孔钴基催化剂费-托合成性能的影响

通过等体积浸渍法制备了双介孔钴基催化剂,采用XRD、BET、SEM、H₂-TPR等手段考察了催化剂的性质,并研究了还原温度对催化剂结构及费托合成催化性能的影响。结果表明,随着还原温度的提高,催化剂活性位增加,活性增加,但增加到一定程度后活性降低,而甲烷选择性随着还原温度的提高逐渐增加,这是反应过程中催化剂表面存在的钴氧化物,使得水煤气反应变得活跃,烃产物移向低碳烃。     

The photoluminescence of Co-Al-layered double hydroxide

We report a new optical behaviour of pure Co-Al-layered double hydroxide (LDH).It was found that the Co-Al-LDH sample could emit fluorescence without any fluorescent substances intercalated.Its excitation spectrum shows a maximum peak near the wavelength 370nm,the maximum emission peak appears at 430 nm and the photoluminescence colour of the Co-Al-LDH sample is blue.This new optical property will be expected to extend the potential applications of LDHs in optical materials field.     

The melting temperature of the most common models of water

The melting temperature of ice I(h) for several commonly used models of water (SPC, SPC/E,TIP3P,TIP4P, TIP4P/Ew, and TIP5P) is obtained from computer simulations at p = 1 bar. Since the melting temperature of ice I(h) for the TIP4P model is now known [E. Sanz, C. Vega, J. L. F. Abascal, and L. G. MacDowell, Phys. Rev. Lett. 92, 255701 (2004)], it is possible to use the Gibbs-Duhem methodology [D. Kofke, J. Chem. Phys. 98, 4149 (1993)] to evaluate the melting temperature of ice I(h) for other potential models of water. We have found that the melting temperatures of ice I(h) for SPC, SPC/E, TIP3P, TIP4P, TIP4P/Ew, and TIP5P models are T = 190 K, 215 K, 146 K, 232 K, 245 K, and 274 K, respectively. The relative stability of ice I(h) with respect to ice II for these models has also been considered. It turns out that for SPC, SPC/E, TIP3P, and TIP5P the stable phase at the normal melting point is ice II (so that ice I(h) is not a thermodynamically stable phase for these models). For TIP4P and TIP4P/Ew, ice I(h) is the stable solid phase at the standard melting point. The location of the negative charge along the H-O-H bisector appears as a critical factor in the determination of the relative stability between the I(h) and II ice forms. The methodology proposed in this paper can be used to investigate the effect upon a coexistence line due to a change in the potential parameters.     

X‐ray studies on the double melting behavior of poly(butylene terephthalate)

The double melting behavior of poly(butylene terephthalate) (PBT) was studied with differential scanning calorimetry (DSC) and wide‐angle X‐ray analysis. DSC melting curves of melt‐crystallized PBT samples, which we prepared by cooling from the melt (250 °C) at various cooling rates, showed two endothermic peaks and an exothermic peak located between these melting peaks. The cooling rate effect on these peaks was investigated. The melt‐crystallized PBT sample cooled at 24 K min^?1 was heated at a rate of 1 K min^?1, and its diffraction patterns were obtained successively at a rate of one pattern per minute with an X‐ray measurement system equipped with a position‐sensitive proportional counter. The diffraction pattern did not change in the melting process, except for the change in its peak height. This suggests that the double melting behavior does not originate from a change in the crystal structure. The temperature dependence of the diffraction intensity was obtained from the diffraction patterns. With increasing temperature, the intensity decreased gradually in the low‐temperature region and then increased distinctly before a steep decrease due to the final melting. In other words, the temperature‐dependence curve of the diffraction intensity showed a peak that is interpreted as proof of the recrystallization in the melting process. The peak temperature was 216 °C. The temperature‐dependence curve of the enthalpy change obtained by the integration of the DSC curve almost coincided with that of the diffraction intensity. The double melting behavior in the heating process of PBT is concluded to originate from the increase of crystallinity, that is, recrystallization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2005–2015, 2001     

Molecular relaxation in the blends of polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide) at low temperature

Molecular relaxation behavior in terms of the α, β, and γ transitions of miscible PS/PPO blends has been studied by means of DMTA and preliminary work has been carried out using DSC. From DSC and DMTA (by tan δ), the observed α relaxation (T_α or T_g) of PS, PPO, and the blends, which are intermediate between the constituents, are in good agreement with earlier reports by others. In addition, the β transition (T_β) of PS at 0.03 Hz and 1 Hz is observed at −30 and 20°C, respectively, while the γ relaxation (T_γ) is not observed at either frequency. The T_β of PPO is 30°C at 0.03 Hz and is not observed at 1 Hz, while the T_γ is −85°C at 0.03 Hz and −70°C at 1 Hz. On the other hand, blend composition-independent β or γ relaxation observed in the blends may be a consequence of the absence of intra- or intermolecular interaction between the constituents at low temperature. Thus it is suggested that at low temperature, the β relaxation of PS be influenced solely by the local motion of the phenylene ring, and that the β or γ relaxation of PPO be predominated by the local cooperative motions of several monomer units or the rotational motion of the methyl group in PPO. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1981–1986, 1998     

Advanced AC calorimetry of polycaprolactone in melting region

The new capabilities of AC calorimetry, when working at frequencies above the classical limit were demonstrated. The appropriate frequency range of classical AC calorimetry was substantially enlarged. It was shown that the advanced AC calorimetry can be applied for studying dynamic heat capacity of polymers in the frequency range 0.1–1 Hz. Thus, the processes with characteristic time as short as ca. 5 s was registered. The advanced AC technique was applied for investigation of the melting kinetics in polycaprolactone. It was found that melting in polycaprolactone is related to an activated process. The activation of the melting process after a step heating is described by a stretched exponent and the decay of the melting by only one exponent at short times. The dependencies of the exponent on temperature and thermal treatment were investigated at frequencies in the range 0.1–1Hz and modulation amplitudes 0.005–0.2 K.     

Determination of the permittivity of nematic liquid crystals in the microwave region

Two 3 mm thick microscope glass plates, having one face plus their two long edges coated by a thick metallic film, are spaced 75 μm apart by mylar spacers. Because of the metallic coatings on the inner faces the structure acts as a single metallic slit. The space between the two coated plates is filled with aligned nematic liquid crystal (E7, Merck/BDH) and the cell is inserted in an absorber aperture. This single metallic slit geometry supports resonant modes when microwaves are incident with their polarization (E-field) perpendicular to the slit. The structure gives a set of Fabry-Perot-like resonant transmission frequencies. These frequencies move when a voltage is applied between the two plates, the liquid crystal being first aligned homogeneously, then realigning homeotropically with the applied field. By minotoring these changes a fast and easy to use procedure for determining the permittivity and its anisotropy for nematic liquid crystals in the microwave region has been developed. The parameters determined for E7 are ε_e = 3.17 (n_e = 1.78 ± 0.01) and ε_o = 2.72 (n_o = 1.65 ± 0.01), (Δn ≈ 0.13) in the 40.0–60.0 GHz region.     

Development of synthetic double helical polymers and oligomers

There is growing interest in the design and synthesis of artificial helical polymers and oligomers, in connection with biological importance as well as development of novel chiral materials. Since the discovery of the helical structure of isotactic polypropylene, a significant advancement has been achieved for synthetic polymers and oligomers with a single helical conformation for about half a century. In contrast, the chemistry of double helical counterparts is still premature. This short review highlights the recent advances in the synthesis, structures, and functions of double helical polymers and oligomers, featuring an important role of supramolecular chemistry in the design and synthesis of double helices. Although the artificial double helices reported to date are still limited in number, recent advancement of supramolecular chemistry provides plenty of structural motifs for new designs. Therefore, artificial double helices hold great promise as a new class of compounds. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5195–5207, 2009     

Performance data of the double pendulum interferometer

The paper describes the optical and electronical concept of a new type of interferometer. The performance of the instrument was demonstrated by measurements of gas absorption spectra and laser emissions. Measured data are compared to theoretical line-by-line calculations.     

Thermal characterization of the intercalation compound ofp-toluenesulfonate into a layered double hydroxide

On intercalation ofp-toluenesulfonate (PTS) into Mg/Al (0.73/0.27) layered double hydroxide (LDH), the layer expanded from 4.77 Å to 17.7 Å, indicating that the plane of PTS was perpendicular to the plane of the LDH layers. Thermal treatment of the PTS intercalate resulted in 82% of the included PTS being evolved as decomposition products. This value was higher than the value of 32.5% obtained with sodium PTS and 43.8% with a mixed sample of PTS and Mg/Al (0.73/0.27) LDH. It was considered that the intercalated PTS in Mg/Al (0.73/0.27) LDH was easy to decompose because interaction between intercalated PTS and Mg/Al (0.73/0.27) LDH was smaller than that between sodium and PTS in sodium PTS.