Monohydric alcohol transport in a rubbery poly(urethan)

Steady-state permeation rates and equilibrium sorption measurements were made as a function of temperature for a series of alcohols in a polybutylene adipate polyurethan. The alcohol series included methanol; ethanol; n-propanol; n-, iso-, sec-, and t-butanol; n-pentanol, n-hexanol, and n-heptanol (all at unit activity). Calculated integral diffusivities of the various penetrants correlated well with effective penetrant size. The solubility coefficients for the various alcohols increased as the difference between the solubility parameters of the polymer and penetrant decreased for the normal alcohol series. The solubility coefficients for the branched alcohol isomers were characterized by values lower than those predicted by the correlation for the normal alcohols; possibly steric hindrance limits sorption on specific polymer sites. A detailed analysis of the system ethanol/poly(butylene adipate-polyurethan) revealed a sigmoidal increase of the diffusion coefficient with increasing penetrant concentration, suggesting a competition between penetrant clustering and polymer plasticization. The diffusion process appears to be time dependent as well as concentration dependent. Anomalies in the diffusion behavior that can reasonably be related to polymer segmental relaxation are present to a much larger degree as temperature is increased. Ethanol sorption was further complicated by positive deviation from Henry's law at activities in excess of 0.2.     

Computational evaluation of Henry's constants and isosteric heats of sorption for Lennard-Jones sorbates in Na-Y zeolite

Henry's constants and isosteric heats of sorption at infinite dilution are calculated for Lennard-Jones sorbates, including the rare gases Ar, Kr and Xe, in Na-Y zeolite. Isosteric heats of sorption are calculated as a function of sorbate size by molecular dynamics (MD) as well as from the temperature dependence of Henry's constants. The MD approach samples the low potential energy regions which form part of the dynamically connected pore space. In contrast, the Henry's constants are evaluated from the infinite dilution limit of the Widom particle insertion method and therefore can, in principle, sample all available, low potential energy pore regions regardless of dynamical connectivity. We show that the difference in the results obtained by the two approaches depends significantly on sorbate size. For a certain range in the sorbate size parameter, the extent of consistency between the two approaches will be sensitive to both temperature and the MD run lengths, providing an interesting illustration of the distinction between available and dynamically connected pore volumes.     

Effects of sample history,time, and temperature on the sorption of monomer vapor by PVC

The sorption of vinyl chloride monomer (VCM) vapor by poly(vinyl chloride) (PVC) resin powders has been studied as a function of time, VCM pressure, temperature, and previous PVC history. In fine powders, sorption occurs in two separable stages, a rapid Fickean diffusion and a slow relaxation-controlled process. Hysteresis in interval sorption-desorption experiments and variable resorption behavior can be related to the relaxation-controlled process. The amount of VCM sorbed shows a pronounced variation with postpolymerization thermal history of the PVC sample; this effect seems to result from the freezing-in of differing “hole volumes” under varied conditions of glassification. The heat of VCM sorption by glassy PVC, ?4.3 kcal/mole, is nearly equal to the heat of condensation of VCM. The complex dependence of sorption behavior upon experimental variables can reasonably be interpreted as reflecting changes in hole volume with postpolymerization history.     

Effect of Dichloromethane on Transport,Thermal, and Thermal‐Mechanic Properties of Amorphous Glass Poly(Ether Imide) Films

Abstract

In this work the interaction effect of dichloromethane on amorphous glassy poly(ether imide) (PEI) films was analyzed from the correlation between transport, thermal, and mechanical properties. The resulting sorption curves were anomalous two‐stage in the solvent activity range 0–0.34 and pseudo‐Fickian for the solvent activity range 0.40–0.50. From a generalized diffusion equation to describe the combination of Fickian and Case II mechanisms we found that the velocity of solvent penetration (v) was higher than the diffusion coefficient (D) for all solvent activities studied. It was observed from the cluster function and the mean size cluster that solvent–solvent interactions may occur at higher solvent activities. Thermal differential scanning calorimetry (DSC) and thermal gravimetric analysis [(TGA) and thermal mechanical (DMTA)] characterization showed that the solvent clusters may act as an antiplasticizer, increasing the elastic modulus of the PEI matrix by 1.9 times. Therefore, a shifting of the β transition was observed at higher temperatures around the glass transition.     

Preparation of zeolite-incorporated PDMS membranes for pervaporation separation of isopropanol-water mixtures

ZSM-5 zeolite-incorporated poly(dimethyl siloxane) membranes were prepared and molecular dispersion of zeolite in the membrane matrix was confirmed by scanning electron microscopy. After studying the behavior of membrane swelling at 30°C, the membranes were subjected to pervaporation separation of isopropanol-water mixtures at 30, 40 and 50°C. The effects of zeolite loading and feed composition on the pervaporation performances of the membranes were analyzed. Both permeation flux and selectivity increased simultaneously with increasing zeolite content in the membrane matrix. This was discussed on the basis of the enhancement of hydrophobicity, selective adsorption, and the establishment of molecular sieving action. The membrane containing the highest zeolite loading (30 mass%) exhibits the highest separation selectivity of 80.84 and flux of 6.78 × 10^?2kg/m²h at 30°C for 5 mass% of isopropanol in the feed. From the temperature dependency of diffusion and permeation values, the Arrhenius activation parameters were estimated. A pure membrane (M) exhibits higher E_p and E_D values compared to zeolite-incorporated membranes, signifying that permeation and diffusion require more energy for transport through a pure membrane, owing to its dense nature. Obviously, zeolite-incorporated membranes require less energy due to their molecular sieving action attributed to the presence of straight and sinusoidal channels in the framework of zeolite. All the zeolite-incorporated membranes exhibit positive ΔH_s values, suggesting that the heat of sorption is dominated by the Henry's mode of sorption.     

Sorption of Organic Solvents in Poly(Dimethyl Siloxane) Membrane. I. Permeant States Quantification using Differential Scanning Calorimetry

The permeant states of various solvents in poly(dimethyl siloxane) (PDMS) film were evaluated using low temperature differential scanning calorirnetry (DSC) on both vapor and liquid penetrants. Water, cyclohexane, benzene, toluene, and m‐xylene may be present in the freezable and nonfreezable state. At low sorption levels, solvents sorbed in PDMS were in the nonfreezable state until a threshold value was reached. Beyond that, the increased solvent sorption values all occurred in a freezable state. The partition pattern between the freezable and nonfreezable states for a vapor penetrant showed an identical trend with that for the liquid penetrant. The maximum nonfreezable amount of solvent in PDMS depended on the solvent's chemical compatibility with the membrane but not on the sorption temperature. Compared with that at 10°C, the higher solvent solubility at 25°C was due to the increase in the freezable solvent content without any change in the maximum nonfreezable content. The permeant states for equilibrium and nonequilibrium samples did not differ from one another.     

Effect of quenching temperature on the structure of isotactic polypropylene films

Films of isotactic polypropylene (iPP) were quenched at different temperatures. Wide-angle x-ray diffractograms for these samples show the presence of the smectic form of iPP at low quenching temperatures and the appearance of mono-clinic form on increasing the thickness of the substrate and the quenching temperature. A quenching temperature higher than 80°C produces only the monoclinic form of iPP, whereas at intermediate temperatures we obtain three-phase amorphous-smectic-crystalline systems. Except for the two-phase amorphous-crystalline system obtained at high temperatures, density values alone do not allow us to obtain the three-phase fractions. We studied the transport properties, sorption, and diffusion of CH₂Cl₂ vapor in these systems to investigate the thermodynamic state of the amorphous component. The behavior of the amorphous component with respect to the diffusion of CH₂Cl₂, which proved identical in all the samples, led us to conclude that at low penetrant activity the smectic phase is not permeable, and therefore we were able to obtain the amorphous fraction in each sample. This value together with density values allowed the determination of the complete composition in terms of three phases for every sample. The crystalline fraction expressed as % mono-clinic form is very well correlated with the reciprocal of the half-height broadening of the (110) diffraction peak at about 2e = 14°.     

Adsorption and diffusion of cyclopentane in silicalite-1: a thermodynamic and kinetic study

The adsorption isotherm, differential thermal gravimetry (DTG), thermal gravimetry (TG), diffusion and thermodynamic parameters of cyclopentane at various adsorption coverages have been investigated using microgravimetric technique over a range of temperature. The differences in equilibrium adsorption capacity and in diffusion coefficient at different temperature are discussed in terms of the characteristics of silicalite-1 and the features of cyclopentane molecule. The heat of sorption Q_st varies significantly with sorption coverage indicating that the adsorption and diffusion mechanism is complex. The dependences of thermodynamic properties like free energy change (ΔG) and entropy change (ΔS) on sorption coverage show a sharp decrease and increase suggesting that the adsorption sites of the silicalite-1 are not energetically uniform to cyclopentane. Two desorption peaks in the DTG and TG curves suggest that two heterogenous binding sites surely exist in silicalite-1 to cyclopentane.     

Anomalous thermal conductivity of frustrated heisenberg spin chains and ladders

We study the thermal transport properties of several quantum-spin chains and ladders. We find indications for a diverging thermal conductivity at finite temperatures for the models examined. The temperature at which the nondiverging prefactor kappa((th))(T) peaks is, in general, substantially lower than the temperature at which the corresponding specific heat c(V)(T) is maximal. We show that this result of the microscopic approach leads to a substantial reduction for estimates of the magnetic mean-free path lambda extracted by analyzing recent experiments, as compared to similar analyses by phenomenological theories.     

Transport properties of poly(ethylene terephthalate)/Rodrun 3000 blends

The transport properties of incompatible blends of poly(ethylene terephthalate) (PET) and a thermotropic liquid crystalline polymer (TLCP) composed of 40 mol% of PET and 60 mol% of p-hydroxybenzoic acid (Rodrun 3000) have been investigated using dichloromethane as permeant. Films, obtained by a blown film extrusion process, were analyzed and compared with the same samples stored 2 and 15 days at 60°C. With respect to the as-blown films, blends submitted to physical aging show a decrease in permeability by a percentage that increases with the amount of the LC phase present and a larger contribution derived from the polymeric matrix. The decrease of permeability is essentially attributed to a lowering of sorption because diffusional behavior for the different samples is the same.     

双温度氩-氮等离子体热力学和输运性质计算

获得覆盖较宽温度和压力范围内的等离子体热力学和输运性质是开展等离子体传热和流动过程数值模拟的必要条件.本文通过联立Saha方程、道尔顿分压定律以及电荷准中性条件求解等离子体组分;采用理想气体动力学理论计算等离子体热力学性质;基于Chapman-Enskog方法求解等离子体输运性质.利用上述方法计算了压力为0.1, 1.0和10.0 atm (1 atm=101325 Pa),电子温度在300—30000 K范围内,非局域热力学平衡(电子温度不等于重粒子温度)条件下氩-氮等离子体的热力学和输运性质.结果表明压力和非平衡度会影响等离子体中各化学反应过程,从而对氩-氮等离子体的热力学及输运性质有较大的影响.在局域热力学平衡条件下,计算获得的氩-氮等离子体输运性质和文献报道的数据符合良好.     

Sorption of Organic Solvents in Poly(Dimethyl Siloxane) Membrane. II. Effect of Sorption on the Polymer Crystals upon Cooling

Polymer crystalline properties in poly(dimethyl siloxane) (PDMS) film after solvation by various solvents was determined using low temperature differential scanning calorimetry (DSC). At various solvent uptake levels, the crystalline thermal properties of the solvated polymer were modified to different extents as revealed by the shifts in crystalline melting point (T_m) and its enthalpy (ΔH_m). Water uptake in PDMS was very limited (<0.01 g/g) and T_m did not significantly change during the sorption process. For toluene and cyclohexane penetrants, T_m moved toward a much lower temperature depending on the sorption levels. At low solvent uptakes, the T_m values decreased linearly with solvent uptakes due to formation of a miscible phase. Beyond a threshold, the T_m remained stable and an additional penetrant fusion peak appeared, implying the onset of a microphase separation phenomenon. The ΔH_m values for the swollen membranes were decreased, with the exception of the water penetrant. This indicates that a lower percentage of polymer chains were involved in the crystalline domain for swollen PDMS.     

Field dependent specific heat and longitudinal magnetization of the quantum magnet layer Cs2CuCl4: Anisotropy effects

We have addressed the specific heat and magnetization of an anisotropic spin-1/2 triangular Heisenberg antiferromagnet Cs₂CuCl₄ in the presence of magnetic field at finite temperature. We have investigated the behavior of thermodynamic properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on thermodynamic properties has also been studied via the bosonic model by Green’s function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the specific heat and longitudinal magnetization in the gapped field induced spin-polarized phase for various magnetic fields and anisotropy parameters. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. Our results show temperature dependence of specific heat includes a peak so that its temperature position goes to higher temperature with increase of magnetic field. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum.     

Thermodynamics and Phase Transition of Topological Dilatonic Lifshitz-Like Black Holes

It is known that scalar-tensor gravity models can be studied in Einstein and Jordan frames. In this paper, a model of scalar-tensor gravity in Einstein's frame is considered to calculate the Lifshitz-like black hole solutions with different horizon topologies. Thermodynamic properties and first order van der Waals-like phase transition are studied, and it is found that the Lifshitz parameter affects the phase structure. In addition, thermal stability is investigated by using the behavior of heat capacity and various methods of geometrical thermodynamics.     

Extension of Planck's law of thermal radiation to systems with a steady heat flux

Planck's law of thermal radiation is limited to equilibrium systems that have a definite temperature and do not carry any heat flux. Here we extend it to steady‐state systems with a constant heat flux. The obtained formulas explicitly describe the spectrum of thermal radiation in every direction and provide a sound basis for the self‐consistent analysis of radiative heat transport across interfaces, gaps, layered and other important structures.     

Structural organization of syndiotactic polystyrene films crystallized in the α form

Syndiotactic polystyrene films were obtained by melt crystallization in the α form. Samples with different crystallinity were produced by varying the thermal treatment of the melt. The structural organization was analyzed by x rays, transport properties, and Fourier transform infrared measurements. The α form is characterized by chains in zigzag planar conformation; it is transformed in dichloromethane into a crystalline form having the chains in a helical conformation. The vapor activity for this transition was obtained for all the crystalline samples. The fraction of impermeable phase, derived from sorption measurements, was consistently found to be higher than the fraction of crystalline phase derived from x rays. This led to the suggestion that in these samples, besides the crystalline phase, there is also a fraction of mesophase, impermeable to dichloromethane vapors at low activity. At activity higher than a critical value this phase becomes permeable, allowing the conformational transition. At activity a = 1, in liquid dichloromethane, the crystalline phase also becomes permeable, and complete transformation into the helical structure is observed.     

Dual-Mode Sorption of Inorganic Acids in Polybenzimidazole (PBI) Membrane

The sorption behaviors of sulfuric, perchloric, and phosphoric acids in polybenzimidazole membranes have been investigated. The results of sorption isotherms are consistent with the general form of a dual-mode sorption isotherm. The dual-mode sorption parameters were found using a least-squares program by fitting experimental data to a dual-mode equation. Results indicate a correlation between permeant properties like acidity, size, and the affinity constant in Langmuir-mode sorption species. Moreover, the results show that the size of the permeants has the dominant effect on Henry's constant. The obtained results for , site saturation constant, in Langmuir-mode sorption in the case of perchloric and phosphoric acids, reveals that the two acid molecules interact with two N?H basic groups in the polybenzimidazole repeat units. But in the case of sulfuric acid, it is shown that sulfuric acid neutralizes some of the basic groups in the polymer by its strong second hydrogen and the obtained value for was 1.25.     

Investigating the thermal conductivity of materials by analyzing the temperature distribution in diamond anvils cell under high pressure

Investigating the thermal transport properties of materials is of great importance in the field of earth science and for the development of materials under extremely high temperatures and pressures. However, it is an enormous challenge to characterize the thermal and physical properties of materials using the diamond anvil cell (DAC) platform. In the present study, a steady-state method is used with a DAC and a combination of thermocouple temperature measurement and numerical analysis is performed to calculate the thermal conductivity of the material. To this end, temperature distributions in the DAC under high pressure are analyzed. We propose a three-dimensional radiative-conductive coupled heat transfer model to simulate the temperature field in the main components of the DAC and calculate in situ thermal conductivity under high-temperature and high-pressure conditions. The proposed model is based on the finite volume method. The obtained results show that heat radiation has a great impact on the temperature field of the DAC, so that ignoring the radiation effect leads to large errors in calculating the heat transport properties of materials. Furthermore, the feasibility of studying the thermal conductivity of different materials is discussed through a numerical model combined with locally measured temperature in the DAC. This article is expected to become a reference for accurate measurement of in situ thermal conductivity in DACs at high-temperature and high-pressure conditions.     

非简谐振动对SiC类石墨烯热输运性质的影响

考虑到原子的非简谐振动,应用固体物理理论和方法,计算了SiC类石墨烯的简谐系数和非简谐系数,得到它的德拜温度、热容量和热导率等随温度的变化规律,探讨了原子非简谐振动对它的热输运性质的影响.结果表明:SiC类石墨烯的德拜温度随温度的升高而在117-126 K之间线性增大,定容比热随温度升高而非线性增大,热导率随温度升高而非线性减小,温度较低时变化较快,而温度较高时变化较慢,并随着温度升高而趋于常量;考虑到非简谐振动后,SiC类石墨烯的德拜温度、定容比热和热导率的值分别大于、小于和大于简谐近似的相应值,温度愈高,其差值愈大,即温度愈高,非简谐效应的影响愈显著;二维平面状的SiC类石墨烯的定容比热和热导率随温度的变化规律,与三维块状SiC晶体总体趋势相同,只是具体数值不同.