Temperature diffusivity and heat conductivity of Langmuir–Blodgett–Kuhn and thin spun-on polymer films

The temperature diffusivity β and heat conductivity κ of thin polymer films were measured at room temperature. Temperature waves were excited at one side of the film and detected at the other side with a pyroelectric foil (PVDF). The dependence of β and κ on chemical and structural parameters have been studied. For the first time, Langmuir–Blodgett–Kuhn multilayer assemblies prepared from “hairy rod” polymers were characterized: μm thin films of stiff polyamides prepared by spincoating exhibit heat conductivities an order of magnitude larger than “classical” polymers.     

以L—B法制造超薄耐热聚合物薄膜的新发展

近年来随着微电子工业的发展,要求发展超薄耐热聚合物薄膜,尤其是聚酰亚胺(PI)超薄薄膜.L-B法能制造超薄PI薄膜.本文叙述了L-B法的发展,并介超了PI耐热聚合物的制法.     

Quantum mechanical calculations of molecular properties and ideal gas heat capacity of difluoromethane

Ideal gas heat capacities are important for the calculation of caloric properties of real fluids. But as shown in the past, they are not always available with required accuracy or are still lacking. In this paper, we combine quantum mechanical calculations and statistical thermodynamics. In order to find a route to a reliable prediction of ideal gas heat capacity data, we applied various quantum mechanical methods differing by computational effort to difluoromethane (CH₂F₂). Only the structural formula and fundamental physical constants enter into the calculations. It is shown that quantum mechanics leads to accurate molecular data. Reliable experimental heat capacity data reveal that an accuracy of better than 0.5% is obtained for the ideal gas heat capacity of difluoromethane.     

The use of advanced calorimetric techniques in polymer synthesis and characterization

Progress in the understanding of polymer synthesis, including the crucial step of initiation and undesired side reactions, and in characterization of polymers, especially their thermal behaviour, are directly related to advances in calorimetric technologies.

In polymer synthesis, since polymerization reactions are highly exothermic, reaction calorimetry (RC) is an appropriate technique for on-line process monitoring. Measurements are non-invasive, rapid, and straightforward. Viscosity increase and fouling at the reactor wall are typical features of many polymerizations. The global heat transfer coefficient, UA, also changes drastically when viscosity increases and affects the accuracy of calorimetric measurements. Our approach was focused on oscillating temperature calorimetry (TOC). Reactions were performed with two different reaction calorimeters, i.e. an isoperibolic calorimeter and a Calvet-type high sensitivity differential calorimeter, respectively. Special attention was paid to the interpretation of the measured signals to obtain reliable calorimetric data. The evolution of heat transfer coefficient was followed by performing two Joule effect calibration experiments, before and after the reaction, and the two values interpolated to obtain the desired profile of UA. A differentiation method based on the convolution of the measured heat flow by the generated one was used for determining the time constants and deconvoluting the measured heat flow.

With respect to polymer characterization, pressure-controlled scanning calorimetry, also called scanning transitiometry, is now a well established technique. The transitiometer was coupled to an ultracryostat to work at low temperature. The assembly was used to follow the pressure effect on phase change phenomena such as fusion/crystallization and glass transition temperature T_g of low molecular weight substances or high molecular weight polymers.     

Recommended vapor pressures for thiophene, sulfolane, and dimethyl sulfoxide

Recommended vapor pressure data for important industrial solvents, thiophene (CAS RN: 110-02-1), sulfolane (CAS RN: 126-33-0), and dimethyl sulfoxide (CAS RN: 67-68-5), were developed by the simultaneous correlation of vapor pressure and related thermal data (heat capacities of condensed phases, ideal gas heat capacities and calorimetrically determined enthalpies of vaporization). For sulfolane and dimethyl sulfoxide, new vapor pressure data were obtained using the static method in the temperature interval from 273 to 308 K. Liquid heat capacities and calorimetric enthalpies of vaporization were taken from the literature and/or determined by Calvet calorimetry. The thermodynamic properties in the ideal gaseous state were calculated using the methods of statistical thermodynamics based on experimental as well as calculated fundamental vibrational frequencies and molecular structure data. Comparisons with literature values are shown for all measured and derived properties.     

Temperature modulated differential scanning calorimetry (TMDSC) in the region of phase transitions. Part 1: theoretical considerations

For temperature modulated differential scanning calorimetry (TMDSC) a simple model, the low pass filter, is presented which allows to see and calculate the influence of heat transfer into the sample on magnitude and phase shift of the modulated part of the measured heat flow rate and the heat capacity determined from it. A formula is given which enables to correct the measured magnitude of the periodic heat flow rate function and the calculated heat capacity in dependence on the thermal resistance and heat capacity of the sample. The correction becomes very important in regions where the heat capacity changes considerably as in the melting region. The approach is successfully tested with model substances with well-known excess heat capacity in the transition region.     

耐热聚氯乙烯的耐热机理研究

用悬浮聚合方法制得了氯乙烯 N 苯基马来酰亚胺 ( 丙烯腈 )共聚物 ,研究了该共聚物的维卡软化点、玻璃化温度、动态力学行为以及形态结构 .发现当耐热组分达到一定含量时 ,耐热性能的增加幅度发生变化、出现两个动态力学内耗峰、形态上出现双连续相结构 .基于这些实验现象 ,提出了“刚性有效网架”可以使耐热性能大幅度提高的观点 ,并探讨了耐热机理 ,给出了物理模型 .讨论了相容性对“刚性有效网架”形成的影响     

Phenomenological study on heat and mass coupling mechanism of waxy crude oil pipeline transport process

Based on the phase equilibrium model of the paraffin wax precipitation in the process of oil pipeline transportation, theory and method of non-equilibrium thermodynamics were applied to obtain the linear phenomenological equations for the cross-interaction of heat and mass transfer during pipeline transport, which were derived from the irreversible entropy production rate equation. Then, the analysis of the irreversible heat flow and the mass flow were carried out, and the mathematical expressions of the phenomenological coefficient of liquid phase, the phenomenological coefficient of solid phase flow, and the heat flow phenomenological coefficient were obtained. Taking a waxy crude oil transportation pipeline in Daqing Oilfield as an example, based on the analysis of liquid–solid phase equilibrium, the irreversible linear phenomenological mechanism of heat and mass coupling in waxy crude oil pipeline transportation was analyzed in detail from three levels: phenomenological coefficients which reflect characteristic of the effect of force on flow in heat and mass transfer; thermodynamic forces which trigger heat and mass transfer; transmitted heat and mass flow density, providing a theoretical basis for the further study of the wax deposition in the process of pipeline transportation.     

Effect of polymer as cosolvent on chemical reactions in solution—II. Effects of polyoxyethylene and polystyrene on the reaction of dansyl chloride with primary amino-ended polyoxyethylene in chloroform

The second-order rate constants for the reaction of 5-dimethylamino-1-naphthalenesulphonyl chloride (dansyl chloride) with primary amino-ended polyoxyethylene in chloroform were measured in the presence of polymers such as polyoxyethylene and polystyrene and compared with those in the presence of low molecular weight models, diethoxyethane and toluene respectively. Both polymers exhibit the polymer effect which is characterized by acceleration of the reaction depending on the degree of polymerization of the polymer cosolvent and on the fraction of the cosolvent. The effect by polymer cosolvents on chemical reactions between a low molecular weight species and a polymer is explained generally in terms of the thermodynamics of polymer solutions.     

Design and construction of an adiabatic calorimeter for samples of less than 1 cm in the temperature range T = 15 K to T = 350 K

A small-scale adiabatic calorimeter has been constructed as part of a larger project to study the thermodynamics of nanomaterials and to facilitate heat capacity measurements on samples of insufficient quantity to run on our current large-scale adiabatic apparatus. This calorimeter is designed to measure the heat capacity of samples whose volume is less than 0.8 cm³ over a temperature range of T = 13 K to T = 350 K. Heat capacity results on copper, sapphire, and benzoic acid show the accuracy of the measurements to be better than ±0.4% for temperatures higher than T = 50 K. The reproducibility of these measurements is generally better than ±0.25%.     

Ion transport in sulfonated polymers

As the focus on proton exchange fuel cells continues to escalate in the era of alternative energy systems, the rational design of sulfonated polymers has emerged as a key technique for enhancing device efficiency. Although the synthesis and characterization of a wide variety of sulfonated polymers have been extensively reported over the last decade, quantitative understanding of the factors governing the ion transport properties of these materials is in its infancy. In this article, we describe the current understanding of the thermodynamics and ion transport in sulfonated polymers. Various strategies for accessing improved transport properties of sulfonated polymers are presented by focusing on their structure-property relationship. The major accomplishment of obtaining well-defined morphologies for these sulfonated polymers is highlighted as a novel means of controlling the transport properties. Recent studies on the thermodynamics, morphologies, and anhydrous transport properties of sulfonated block copolymers comprising ionic liquids, geared towards high temperature polymer electrolyte membranes as a prospective technology, are also expounded. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Experimental and theoretical study of thermodynamic properties of levoglucosan

The heat capacity of levoglucosan was measured over the temperature range (5 to 370) K by adiabatic calorimetry. The temperatures and enthalpies of a solid-phase transition and fusion for the compound were found by DSC. The obtained results allowed us to calculate thermodynamic properties of crystalline levoglucosan in the temperature range (0 to 384) K. The enthalpy of sublimation for the low-temperature crystal phase was found from the temperature-dependent saturated vapor pressures determined by the Knudsen effusion method. The thermodynamic properties of gaseous levoglucosan were calculated by methods of statistical thermodynamics using the molecular parameters from quantum chemical calculations. The enthalpy of formation of the crystalline compound was found from the experiments in a combustion calorimeter. The gas-phase enthalpy of formation was also obtained at the G4 level of theory. The thermodynamic analysis of equilibria of levoglucosan formation from cellulose, starch, and glucose was conducted.     

Determination of the activity of a molecular solute in saturated solution

Prediction of the solubility of a solid molecular compound in a solvent, as well as, estimation of the solution activity coefficient from experimental solubility data both require estimation of the activity of the solute in the saturated solution. The activity of the solute in the saturated solution is often defined using the pure melt at the same temperature as the thermodynamic reference. In chemical engineering literature also the activity of the solid is usually defined on the same reference state. However, far below the melting temperature, the properties of this reference state cannot be determined experimentally, and different simplifications and approximations are normally adopted. In the present work, a novel method is presented to determine the activity of the solute in the saturated solution (=ideal solubility) and the heat capacity difference between the pure supercooled melt and solid. The approach is based on rigorous thermodynamics, using standard experimental thermodynamic data at the melting temperature of the pure compound and solubility measurements in different solvents at various temperatures. The method is illustrated using data for ortho-, meta-, and para-hydroxybenzoic acid, salicylamide and paracetamol. The results show that complete neglect of the heat capacity terms may lead to estimations of the activity that are incorrect by a factor of 12. Other commonly used simplifications may lead to estimations that are only one-third of the correct value.     

Prediction of the decay resistance of heat treated wood on the basis of its elemental composition

The effect of heat treatment temperature on the elemental composition of Scots pine sapwood (Pinus sylvestris) has been investigated in the range of temperatures between 220 and 250 °C. The results revealed an important increase of carbon content, while oxygen content significantly decreases. Independently of the heat treatment temperature, elemental composition is strongly correlated with the mass losses due to thermal degradations. Carbon content as well as O/C ratio seem to represent valuable markers to estimate wood degradation after heat treatment. Heat treated specimens were exposed to fungal decay using the brown rot fungus Poria placenta and the weight losses due to fungal degradation were determined. Correlations between weight losses recorded after fungal exposure and elemental composition indicated that carbon content or O/C ratio can be used to predict wood durability conferred by heat treatment allowing us to envisage the development of a proper method to evaluate the quality of heat treated wood and predict its durability. These results also confirm that chemical modifications of wood cell wall polymers are the main factors responsible for wood durability improvement against fungal decay after heat treatment.     

Thermodynamics of inelastic deformation of amorphous and crystalline phases in linear polyethylene

Thermodynamic parameters (work W _def and heat Q _def) of inelastic deformation (uniaxial compression up to ɛ_def = 50%) are measured for six samples of high-molecular-mass linear PE at room temperature under the regime of active loading. Energy excess ΔU _def accumulated by the samples subjected to loading are calculated in terms of the first law of thermodynamics. All thermodynamic characteristics linearly increase with crystallinity χ of PE, thus making it possible to extrapolate their values to χ = 0 and 100% and to find the contributions of the amorphous and crystalline phases of the polymer to the overall thermodynamics of deformation. Both of the PE phases contribute to W _def and ΔU _def, while the crystalline phase alone contributes to heat Q _def. At ɛ ≥ 30%, the energy contribution from the amorphous phase exceeds that from the crystalline phase. A comparison between the plastic behavior of PE crystals and glassy polymers demonstrates that PE crystallites are easier deformed (requires less work W _def) than glassy polymers. At the same time, the amorphous phase of PE is harder to deform (requires more work W _def and stores more energy ΔU _def) than noncrystalline rubbers, apparently because of the deformation of tie chains. The thermodynamic characteristics of deformation are compared for three materials: crystalline metals, PE, and glassy polymers. The similarities and differences in their plastic behaviors are considered.     

Heat flux calorimetry in intermetallic compound–H2(g) systems: heat measurements and modeling in the low pressures range

A heat conduction calorimeter has been used to determine enthalpies of solid–gas reactions in systems, such as intermetallic compounds–H₂(g). It is shown that the significance of the heat measurements must be carefully analyzed by controlling several parameters, which may influence the heat transfer conditions during the absorption and desorption reactions.

For this type of reaction, the measured heat flow is strongly dependent on the heat transfers through the gas phase in the low pressure range (Knudsen regime). It is demonstrated, experimentally and confirmed with simple models, that heat measurements can provide erroneous enthalpies due to our inability to account for the unavoidable modifications of the heat losses in the transition region. Experiments were carried out on the ZrNi–H₂ system.     

Some elements in specific heat capacity measurement and numerical simulation of temperature modulated DSC (TMDSC) with R/C network

One important application of temperature modulated DSC (TMDSC) is the measurement of specific heat of materials. In this paper, a thermal resistance/capacitance (R/C) numerical model is used to analyze the effects of experimental parameters and calibration on the measurement of specific heat in TMDSC under isothermal conditions. The actual TMDSC experiments were conducted with sapphire and pure copper samples, respectively. Both simulation and experiments showed that in TMDSC, the measured sample specific heat is a non-linear function of many factors such as sample mass, the heat transfer properties of the TMDSC instrument, temperature modulation period, the heat capacity difference between calibration material and the test material, but modulation amplitude has very little effect on the results. The typical behavior of a heat flux type TMDSC can be described as a low pass filter in terms of specific heat capacity measurement when the instrument heat transfer properties are taken into account. At least for metallic materials, where the temperature gradient inside the sample can normally be ignored, the sample should be chosen in such a way that its total heat capacity (mass times specific heat) is close to that of the calibration material in order to get a more accurate result. Also, a large modulation period is beneficial to improving the test accuracy.     

Inverse-gas chromatography and the thermodynamics of sorption in polymers

In this review, the development of inverse gas chromatography (IGC) is briefly described, the role of A.A. Tager??s studies is indicated, and the principles of using the IGC method to solve problems of the thermodynamics of sorption of gases and vapors in polymers are formulated. The IGC method was originally developed by Guillet??s school to study the thermodynamics of sorption in polymers above their glass-transition temperatures; later, it was generalized and extended to the study of sorption processes below the glasstransition temperature in high-fractional free-volume polymers. These polymers exhibit specific features, such as strong exothermicity of mixing (??H _m ? 0), dependence of ??H _m on the size of the sorbate molecule, and high solubility coefficients. Chromatographic studies of sorption in the AF1600 amorphous perfluorinated polymer above and below its glass-transition temperature made it possible to test a new thermodynamic model that describes the sorption of gases and vapors in glassy polymers.