Behavior of pressure dependence of melting temperatures in aromatic polyesters: Influence of polymer structure

The thermal behavior of three aromatic polyesters in a homologous series, poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) was studied under hydrostatic pressure up to 200 MPa by using a high pressure differential thermal analysis apparatus. Confining fluid high pressure dilatometer was used to establish the volume–temperature curves (in both solid and liquid regions) from which volume change on melting of these polyesters at atmospheric pressure was determined. Single endothermic peak was seen for PET and PTT, whereas PBT showed double peaks above 50 MPa. Pressure coefficient of melting temperature at atmospheric pressure (dT_m/dp₍₀₎), was obtained from the quadratic fit. The dT_m/dp₍₀₎ for PTT was newly determined to be 0.445 KMPa^?1, whereas for PET and PBT were 0.503 and 0.455 KMPa^?1, respectively, comparable to reported values. The dT_m/dp₍₀₎ exhibited the odd‐even behavior corresponding to odd and even number of methylene groups in the repeat unit. Enthalpy and entropy of fusion had the most influence on this coefficient. Entropy related to conformational and volume change were evaluated and the former was found to have a significant impact on the value of dT_m/dp₍₀₎. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1799–1808, 2009     

Ferroelectric phases in non-symmetric achiral bent liquid crystals towards ambient temperatures: a novel series with oxadiazol as central moiety

Extensive survey carried out in bent liquid crystals (BLCs) exhibiting ferroelectric (FE) phases suggested for the design of non-symmetric (NS) frame. Novel series of BLCs (C₈C_m) with distinct lateral moieties and heterocyclic central (oxadiazole) moiety, viz., octyl 4-(5-(4´-(alkyloxy) biphenyl-4-yl)-1,2,4-oxadiazol-3-yl)benzoates, are reported. NS BLC frame is realised by incorporating differing number of aromatic cores and varied length of end chains in the lateral moieties. Lateral moiety with biphenyl core is prepared by Suzuki coupling. Purity of the BLC product is confirmed by ¹H NMR and elemental analysis. LC phases exhibited by C₈C_m series of BLCs for m = 8, 10, 12, 15 and 16 are characterised by polarisation optical microscopy (POM), differential scanning calorimetry (DSC) and spontaneous polarisation (P_S) techniques. C₈C_m series are found to exhibit SmA, CrystalB, B₂, B₅, SmG and SmE phase variance. SmG occurs as monotropic phase. Temperature variation of P_S(T) studied in FE B₂ and B₅ phases by field reversal method infers a moderate P_S value of ~80–100 nC · cm^?2. Order parameter growth in FE B₂ and B₅ phases is analysed through P_S(T). Normalised order parameter θ_N exhibits asymptotic behaviour with universal temperature T^U. Influence of aromatic cores and length of end chains (in lateral moieties) on the thermal stability of FE phases is discussed in the wake of the data on other BLCs.     

Melting points and other properties of ionic liquids,with emphasis on the pressure dependence

The focus of this letter is on melting points (T _m) of ‘green’ ionic liquids, which have values of T _m around room temperature. To aid in their chemical interpretation, we place some emphasis on T _m as a function of pressure p, in cases where such experimental information is available. Finally, some comments are made on the effects of pressure via isothermal compressibility κ _T and the velocity v _s of sound. Some measurements of κ _T and v _s as a function of p are invoked.     

Ion association and departure from additivity of equivalent conductance as a function of pressure

The equivalent conductance of mixtures of 0.01 equivalent/liter solutions of MgCl₂ and Na₂SO₄ were measured as a function of pressure at 25°C. Departures from additivity are used to infer the pressure dependence of the concentration of MgSO₄ ion pairs. The results are consistent with the pressure dependence of the molal dissociation constant of MgSO₄ obtained from pressure conductance studies on aqueous solutions of MgSO₄.     

金属铜升温熔化过程的分子动力学模拟

采用分子动力学方法模拟了金属铜的升温熔化过程.原子间作用势采用FS (Finnis-Sinclair)势，结构分析采用双体分布函数(PCF)、均方位移(MSD)等方法.计算结果表明,在连续升温过程中，金属铜在1444 K熔化，在该熔化点的扩散系数为4.31×10－9 m2•s－1.上述结论与实验值相当接近，并且比之采用EAM镶嵌原子势所作模拟得到的结果更佳，说明FS势可以用来处理象液铜这样较复杂的无序体系.本文指出了升温速率在金属熔化过程中所起的作用.     

Some thermodynamic quantities of n-alkanes as a function of chain length

Summary Results from high pressure dilatometry onn-alkanes and linear polyethylene and literature data yield a linear relation between specific volume, entropy and enthalpy of fusion, the reciprocal melting temperature and 1/n, wheren denotes the number of C-atoms per molecule. Extrapolating towards infiniten one always obtains polyethylene data.The differences in the properties ofn-alkanes and polyethylene can be ascribed to the influence of the chain ends. Assuming entropy and enthalpy contributions from these chain ends as made probable by a molecular model one can quantitatively explain then-dependence of the above mentioned quantities including their pressure dependence.With 10 figures and 2 tables     

Internal pressure and solubility parameter as a function of pressure

The main goal of this work was to measure the solubility parameter of a complex mixture, such as a crude oil, especially as a function of pressure. Thus, its definition is explained, as well as the main approximations generally used in literature. Then, the internal pressure is investigated, since it is presented as an alternative of the solubility parameter. In this work, the assumption that internal pressure is a measure of the physical solubility parameter was made, i.e. representing the dispersion and polar forces. As for the pressure influence, it was seen that internal pressure reaches a maximum contrary to solubility parameter.An indirect method was chosen to estimate internal pressure, using thermal expansivities (determined by microcalorimetry) and isothermal compressibilities (determined by density measurements). The uncertainty is within 2% for the expansivity and 0.1% for the density. Five pure compounds (four hydrocarbons and 1 alcohol) were investigated at 303.15 K and up to 30 MPa, as well as a dead crude oil. The “physical” solubility parameter is slightly increasing with pressure (up to 0.8 MPa^1/2 for cyclohexane) and, at 0.1 MPa, the difference with literature data is less than 1 MPa^1/2 for hydrocarbons. On the contrary, the difference reaches 9 MPa^1/2 for ethanol as expected, due to the presence of hydrogen bonding. A dead crude oil was also studied and its solubility parameter is within the expected range.Two cubic equations of states (Peng–Robinson and Soave–Redlich–Kwong) were able to approximate the “physical” solubility parameter of n-heptane (within 0.2 MPa^1/2), providing that the volumes were measured and used as input. The Peng–Robinson equation gave somewhat better results.     

Crystal structures and phase behaviour of acetaldehyde-d4: a study by high-resolution neutron powder diffraction and calorimetry

High-resolution neutron powder diffraction is particularly suited for structure solution and refinement of low-melting point organic crystals of moderate complexity. Here we present the ab initio structure solution and refinement of stable-phase and metastable-phase perdeuterated acetaldehyde (m.p.: 151 K). In the stable phase, the molecule crystallises in the space group P2₁/c (no. 14) with a=3.9069(1) Å, b=5.4224(1) Å, c=12.1868(1) Å, β=94.2970(2)° at 5 K, Z=4. In the metastable phase, the molecule crystallises in the space group Pna2₁ (no. 33) with a=5.1973(1) Å, b=6.9791(1) Å, c=6.9712(1) Å at 5 K, Z=4. The metastable to stable phase transition is characterised by heat capacity measurements.     

Structural and vibrational characterization of the organic semiconductor tetracene as a function of pressure and temperature

Neutron powder diffraction and inelastic neutron scattering measurements were performed on crystalline tetracene, a molecular semiconductor of triclinic crystal structure that adopts a herringbone layered motif, as a function of pressure up to 358 MPa. In combination with theoretical and simulated computations, these measurements permit detailed characterization of the structural and vibrational changes of tetracene as a function of pressure. Powder diffraction at 295 K reveals anisotropic modification of the crystal structure with increasing pressure. Particularly, the unit cell parameters associated with the two-dimensional herringbone layers of the solid state structure displayed continuous change at all measured pressures, whereas perpendicular to the herringbone layers the structure remains relatively unchanged. The measured compressibilities along the [1 0 0], [0 1 0], and [0 0 1] crystal axes are −3.8 × 10⁻⁴, −1.9 × 10⁻⁴, and −3.4 × 10⁻⁴ Å/MPa, respectively. Inelastic neutron scattering spectra were collected at several pressures in the 25–75 and 0–25 meV energy ranges using a filter analyzer and a Fermi chopper time-of-flight spectrometer, respectively. Assignment of the spectral peaks to specific intramolecular vibrational modes has been accomplished using ab initio density functional theory calculations and the low energy lattice phonon modes were interpreted from the results of molecular dynamics simulations at 1 atm and 358 MPa. Anisotropic behavior parallel to that observed in the structural measurements is also apparent in both the intramolecular and lattice phonon vibrational dynamics. Intramolecular vibrations having atomic displacements entirely within the plane of the molecule’s aromatic ring remain unchanged with increasing pressure while vibrations with atomic displacements perpendicular to the molecular plane shift to higher energy. The lattice phonons display a similar anisotropy with increasing pressure. Phonon modes propagated within the herringbone layer are significantly shifted to higher energy with increasing pressure relative to the modes with displacements primarily perpendicular to the layers. Overall, both the planar internal geometry and the layered arrangement of the tetracene molecules significantly influence the observed structural and vibrational behavior with increasing pressure.     

19F NMR chemical shifts of CF4 in CO2 over a wide pressure range at different temperatures

¹⁹F NMR chemical shifts of CF₄ in CO₂ under extremely dilute concentrations were precisely determined at 299.8, 314.4 and 328.9 K over a wide range of pressure between 0.4 and 33 MPa. The solvent‐induced chemical shift, where the bulk magnetic susceptibility correction was made, was quantitatively expressed as a function of CO₂ density. Copyright © 2002 John Wiley & Sons, Ltd.     

Dynamics in ferro- and antiferroelectric phases of a liquid crystal with fluorinated molecules as studied by dielectric spectroscopy

For 1-[3-fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-2-[4-2,2,3,3,4,4,4-heptafluorobutoxybutoxy)biphenyl-4-yl]ethane (1F7), built of chiral molecules, results of dielectric measurements of liquid-crystalline and solid phases are presented. Rich polymorphism of liquid-crystalline (SmC*, SmC*_A and SmI*_A) phases as well as of solid (Cr1 and Cr2) phases were observed down to –130°C. At a frequency range from 0.1 Hz to 3 MHz, the relaxation processes were detected in ferroelectric SmC*, antiferroelectric SmC*_A and highly ordered SmI*_A smectic phases. The mechanism of complex dynamics (moleculear and collective) was identified with the help of the bias field. Vitrification of conformationally disordered crystal phase Cr2 was found in accordance with calorimetric observations.     

环氧乙烷和环氧丙烷共聚物及其盐复合物的结晶与熔融

环氧乙烷和环氧丙烷共聚物及其盐复合物的结晶与熔融齐力，林云青，陈东霖（中国科学院长春应用化学研究所长春１３００２２）关键词环氧乙烷环氧丙烷共聚物，高分子固体电解质，结晶，熔融聚环氧乙烷（ＰＥＯ）及其盐复合物等￣［１，２］是一类高分子固体电解质，但ＰＥ...     

熔盐法合成LiNi0.5Mn1.5O4及电化学性能

以一定比例的LiCl-LiNO_3为低熔点共混物,采用熔盐法合成了电化学性能良好的LiNi_(0.5)Mn_(1.5)O_4,XRD表征结果显示产物为单一尖晶石相,SEM表征显示出材料良好的晶形,充放电测试结果显示出材料在4.7V平台附近有较大的可逆容量,在4.1V平台附近仅有较少的可逆容量。文章讨论了影响产物晶形和性能的各种因素,建议通过退火、改变合成气氛来消除4.1V平台的产生;研究结果还显示,容量的损失主要发生在第一次放电过程中在高电位区时的电解液的氧化分解.建议通过更换适合在高电位条件下工作的电解液来克服此问题;同时,通过调整低熔点共混物的配比、气氛、反应时间等条件可以实现对产物的结晶形态和大小进行适当的控制,显示了该方法在制备LiNi_(0.5)Mn_(1.5)O_4材料中的应用前景.     

分子转动惯量与正烷烃熔沸点的预测

在分子转动模型基础上,以半经验分子轨道(AM1)方法计算分子的转动惯量及其它结构参数,获得15个正烷烃的沸点和熔点的多元线性回归方程。其中正烷烃的沸点与短轴转动惯量(c)和碳原子数(n)相关 (bp=-147.2-0.01189c+36.17n, R=0.9985, SD=6.97), 而熔点与分子的长轴转动惯量(a)、短轴转动惯量(b,c)及重定向能(E)相关(mp=-260.3+15.70a +19.74b -19.76c +1.30E, R=0.99991, SD=1.07)。分子的长轴转动惯量和重定向能与正烷烃熔点的奇－偶锯齿形规律相关。     

熔盐法合成LiNi0．5Mn1．5O4及电化学性能

以一定比例的LiCl-LiNO3为低熔点共混物，采用熔盐法合成了电化学性能良好的LiNi0.5Mn1.5O4，XRD表征结果显示产物为单一尖晶石相，SEM表征显示出材料良好的晶形，充放电测试结果显示出材料在4．7V平台附近有较大的可逆容量，在4．1V平台附近仅有较少的可逆容量。文章讨论了影响产物晶形和性能的各种因素，建议通过退火、改变合成气氛来消除4．1V平台的产生；研究结果还显示，容量的损失主要发生在第一次放电过程中在高电位区时的电解液的氧化分解，建议通过更换适合在高电位条件下工作的电解液来克服此问题：同时，通过调整低熔点共混物的配比、气氛、反应时间等条件可以实现对产物的结晶形态和大小进行适当的控制，显示了该方法在制备LiNi0.5Mn1.5O4材料中的应用前景。     

Solubilities of cefodizime disodium in aqueous alcohol mixtures at atmospheric pressure and different temperatures

Using dynamic method and the laser monitoring observation technique, the solubility of cefodizime disodium in water + (ethanol, 1-propanol, and 2-propanol) was measured as a function of temperature from 278.15 K to 318.15 K under atmospheric pressure. The experimental data were correlated with a simple model of molecular thermodynamics for solubility of solid in liquid. The model parameters were fitted, and the solution enthalpies Δ_solH and solution entropies Δ_solS were estimated. Δ_solH and Δ_solS are all positive. The endothermic effect of solution process may be due to the fact that the newly bond energy between cefodizime disodium and solvent molecules is not powerful enough to compensate the energy needed to break the original association bond in various solvents, and the system needs to absorb heat from surroundings and manifests as Δ_solH > 0. The reason for the entropy increase during the dissolution process is that the solutes disrupt the alignment of solvent molecules and therefore reduced the degree of order of the system while they were dissolved in various solvents. The positive Δ_solH and Δ_solS revealed that the dissolution process of cefodizime disodium was an entropy-driven process.     

Thermal expansion of polymers submitted to supercritical CO2 as a function of pressure

Interactions of polymers with compressed supercritical CO₂ has been studied by using pressure‐controlled scanning calorimetry (PCSC). Global cubic thermal expansion coefficients (α_{pol‐g‐int}) for medium density polyethylene (MDPE) and poly(vinylidene fluoride) (PVDF) saturated with supercritical CO₂ have been determined at 352.4 K over the pressure range from 0.1 MPa to 100 MPa. In both cases, the isotherms of global α_{pol‐g‐int} exhibit minima near 20 MPa. At pressures below the minimum, α_{pol‐g‐int} for the PVDF–CO₂ system are higher than for the MDPE–CO₂ system, while at pressures above the minimum the opposite was observed. This proves that incorporation of CO₂ in PVDF is stronger than in MDPE. The appearance of the minimum is attributed to the action of compressed CO₂ molecules, which at higher pressures are forced to enter deep inside the interstitial or other voids in the polymer and cause their mechanical distension, which must be associated with an endothermic effect. The measurements have been performed on polymers used for fabrication of pipelines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:185–194, 2006     

Crystal structures of mesogens with a bent molecular shape: 4,6-dichloro-1,3-phenylene bis-[4-(4-n-alkyloxy-phenyliminomethyl)benzoates]

The crystal and molecular structures of hexyloxy (3a) and heptyloxy homologues (3b) of mesogenic 4,6-dichloro-1,3-phenylene bis[4-(4-n-alkyloxy-phenyliminomethyl)benzoates] have been determined by X-ray analyses. Both compounds crystallize in the triclinic space group with two molecules in unit cells of following dimensions. 3a: a=8.340(2), b=13.143(4) and c=19.364(6) Å; =96.36(4), β=93.33(4) and γ=103.07(1)°; 3b: a=8.738(2), b=15.850(4) and c=17.618(5) Å; =115.73(2), β=90.82(2) and γ=95.49(2)°. The structures were solved by direct methods and refined on F² to R values of R1=0.046 (3a) and 0.094 (3b).

The molecular structures of 3a and 3b are discussed in detail, especially in view of the correlation between molecular conformation (banana- or rod-shaped molecules) and liquid crystalline behaviour (observed mesophases). It can be shown for 3a and 3b that the molecules are not strongly bent and not so far from the rod-like shape. Crystal packing of the mesogens is characterized by a parallel arrangement of the strongly interlocked molecules.     

Diffusion of linear aliphatic esters in polyethylene as a function of chain length of the esters,pressure and temperature

Diffusion of linear aliphatic mono- and diesters (C _N ) havingN main chain atoms (N=13–68) in bulk medium-density polyethylene (MDPE) has been studied under hydrostatic pressures up to 2500 bar at temperatures between 60°C and 125°C. Three triglycerides, phenyl stearate, and p-aminoazobenzene (pAAB, 80°C) as the diffusants and low-density (LDPE) and high-density (HDPE) polyethylenes as polyethylene substrate were used for comparison. Diffusion coefficientD was determined from concentration distribution of the diffusants through stacked PE sheets as substrate. Regarding the linear esters at 90°C, the relationshipD N holds at constant pressures. Under the atmospheric pressure, became –2.10 in accordance with de Gennes's proposal (1971)D N ^–2 as well as with the experimental results reported by Klein and Briscoe (1979) forN larger than 30.D's for the glycerides deviate from the relationshipD N ^–2 toward the smaller values by comparison at the sameN. The exponent is pressure-dependent. It decreases with increasing pressure according to =–2.10–0.000942P, whereP is measured by the unit of bar. Plots of lnD vsP for all the diffusants show linear relationships with negative slopes, from which activation volume for the diffusion V was calculated. At 90°C, V increases slowly with increasingN and increasingV _Ki, the intrinsic molecular volume of the diffusant, from 39.3 cm³/mol for ethyl caprate (C ₁₃,V _Ki=136 cm³/mol) to 76.8 cm³/mol for behenyl behenate (C₄₅,V _Ki=466 cm³/mol). Observed V s are explainable on the basis of the reptation mode of the chain molecule diffusion. V s for C₂₅ and C₄₅ are found to increase with increasing degree of crystallinity where MDPE, heat-treated MDPE, LDPE, and HDPE were used. The results obtained by varying temperature are as follows. V for C₄₅ was always found to be larger than C₂₅. Both decreased linearly with increasing temperature, giving two linear lines with different slopes whose extensions intersected at 132°C, the melting point of the MDPE, where the difference in V disappeared. The apparent activation energiesE _Ds for the diffusion of C₂₅ and C₄₅ increased linearly with increasing pressure, whose slopes are explainable according toE _D=E ₀+PV [1-(dln V /dlnT) _P ].     

Specific volume of polysulfone as a function of temperature and pressure

The pressure–volume–temperature (PVT) properties of a commercial polysulfone derived from bisphenol A and 4,4′-dichlorodiphenylsulfone are studied experimentally and theoretically in the temperature range 30–370°C and for pressures to 2000 kg/cm². PVT surfaces are determined for an annealed glass, formed under zero pressure, and for the melt. Two glass-transition lines must be distinguished: T(P) which is the intersection of the glass and melt PVT surfaces, and T_g(P), which is obtained by pressurizing the melt isothermally. The application of Ehrenfest-type equations to these transitions are discussed. The Prigogine–Defay ratio r = Δ_kΔC_p/TV(Δα)² at P = 0 is found to be equal to 0.95 (±20%), using ΔC_p data determined on identical samples. The melt data is compared with the Simha–Somcynski hole theory, using the reducing parameters V^* = 0.788 cm³/g, T^* = 12,560°K, P^* = 10,875 bar. The hole fraction appearing in the theory is found to be constant along T(P), but the glass PVT relationship cannot be reproduced by using the Simha–Somcynsky theory together with the assumption that the hole fraction remains constant in the glass. At P = 0 the hole fraction must be allowed to decrease with decreasing temperature, but at a slower rate than in the melt.