A new method of fitting approximate vibrational spectra to heat capacities of solids with Tarasov functions

A new, least-squares optimization method with interpolation is devised to fit skeletal vibrational heat capacities to the two parameters θ₁ and θ₃ in the Tarasov function used for heat capacity calculations of linear macromolecules. When heat capacities are available in the proper temperature range, θ₁ and θ₃ can be determined uniquely in a single computer run. Appended to our Advanced THermal Analysis System (ATHAS), this new method offers an improvement in analyzing heat capacity data and facilitates the systematic study of the physical significance of θ₁ and θ₃ values for all polymers and related molecules of the ATHAS data bank.     

Thermophysical properties of macromolecules in the block state

The macromolecules of linear polymers usually consist of regular helices. The paper presents the results of investigation of the concentration, thermal expansion coefficient and vibration amplitude of such helices at different temperatures. These parameters were determined from temperature dependences of the intensity, frequency and halfwidth of regular bands in IR and Raman spectra of polymers.

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Zusammenfassung Die Makromoleküle linearer Polymere zeigen gewöhnlich Helixstruktur. Es wurden Konzentration, Wärmeausdehnungskoeffizient und Schwingungsamplitude derartiger Helizes bei verschiedenen Temperaturen untersucht. Diese Parameter wurden anhand von Intensität, Frequenz und Halbwertbreite der Normalbanden in IR- und Raman-Spektren von Polymeren bestimmt.

     

Specific heat capacity and Debye temperature of zirconia and its solid solution

Specific heat C_P of zirconia and yttria stabilized zirconia doped or not with erbia and ceria was measured from 128 to 823 K and of yttria stabilized zirconia doped with erbia and plutonia from 443 to 1573 K. The new determined data were modelled using Debye theory. Data for the tetravalent oxide and for the studied solid solutions show that the extended Dulong and Petit law in Neumann-Kopp rule is verified for zirconia and the quaternary compounds. The Debye temperature of zirconia (590 K) and its yttria, erbia and ceria doped solid solutions (575-625 K) derived from these C_P measurements between 150 and 823 K is discussed and compared with that reported for other tetravalent metal oxides.     

Conformational contribution to the heat capacity of the starch and water system

The heat capacities of starch and starch—water have been measured with adiabatic calorimetry and standard differential scanning calorimetry and are reported from 8 to 490 K. The amorphous starch containing 11–26 wt % (53–76 mol %) water shows a partial glass transition decreasing from 372 to 270 K, respectively. Even the dry amorphous starch gradually increases in heat capacity above 270 K beyond that set by the vibrational density of states. This gradual increase in the heat capacity is identified as part of the glass transition of dry starch that is, however, not completed at the decomposition temperature. The heat capacities of the glassy, dry starch are linked to an approximate group vibrational spectrum with 44 degrees of freedom. The Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations with the parameters Θ₁ = 795.5 K, Θ₂ = 159 K, and Θ₃ = 58 K for 19 degrees of freedom. The calculated and experimental heat capacities agree better than ±3% between 8 and 250 K. Similarly, the vibrational heat capacity has been estimated for glassy water by being linked to an approximate group vibrational spectrum and the Tarasov equation (Θ₁ = 1105.5 K and Θ₃ = 72.4 K, with 6 degrees of freedom). Below the glass transition, the heat capacity of the solid starch—water system has been estimated from the appropriate sum of its components and also from a direct fitting to skeletal vibrations. Above the glass transition, the differences are interpreted as contributions of different conformational heat capacities from chains of the carbohydrates interacting with water. The conformational parts are estimated from the experimental heat capacities of dry starch and starch—water, decreased by the vibrational and external contributions to the heat capacity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3038–3054, 2001     

Computation of the generalized Debye functionsδ(x,y) andD(x,y)

Automatic computer programs (BASIC-PLUS) are developed to calculate Debye functions also for non integer exponents. Functions of this type occur in the heat capacity analysis of polymer crystals, if simple continuum approximations are used. The heat capacity of completely crystalline polyethylene is calculated and compared with experimental data.     

Modeling the heat flow and heat capacity of modulated differential scanning calorimetry

Modulated differential scanning calorimetry (MDSC) uses an abbreviated Fourier transformation ?r the data analysis and separation of the reversing component of the heat flow and temperature signals. In this paper a simple spread-sheet analysis will be presented that can be used to better understand and explore the effects observed in MDSC and their link to actual changes in the instrument and sample. The analysis assumes that instrument lags and other kinetic effects are either avoided or corrected for.     

The structure of diluted binary solutions of amides according to the heat capacity data

The specific heat capacities of hexamethylphosphoric triamide, diethylpropionamide, their aqueous solutions, and mixtures of hexamethylphosphoric triamide with formamide were measured in the temperature range from 288.15 to 318.15 K. The dependences of the partial molar heat capacity of aqueous solutions of amides on the composition of the mixture have maxima in the region of 0.02–0.04 molar fractions of amide. The maximum on a similar dependence for solutions of hexamethylphosphoric triamide corresponds to the concentration of 0.01 molar fractions. The conclusion on the formation of solvates (hydrates) in the systems studied was made. The heat capacity coefficients of pair and triple interactions were calculated in terms of the McMillan-Mayer theory. A change in the heat capacity characteristics with the temperature change was analyzed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2479–2483, December, 1998.     

Importance of heat capacity effects in the association of hydrocarbon moieties in aqueous solution

Values are reported for changes in heat capacity that accompany the formation of hydrocarbon-hydrocarbon dimers and hydrocarbon-polar hydrocarbon derivative dimers in dilute aqueous solution. Highly negative C _p ^o are obtained; the enthalpy changes, endothermic at room temperature, tend to decrease to zero in the range 50 to 80°C. A discussion is given of the importance of heat capacity effects in relation to the stability of hydrophobic association complexes.     

An adiabatic low-temperature calorimeter for heat capacity measurement of small samples

A small sample adiabatic calorimeter for measuring heat capacities in the temperature range 60–350 K using the Nernst method has been constructed. The sample cell of the calorimeter is 6 cm³ in the internal volume, equipped with a miniature platinum thermometer and surrounded by two adiabatic shields. Two sets of 6-junction chromel-copel thermocouples were mounted between the cell and the shields to indicate the temperature differences between them. The adiabatic conditions of the cell were automatically controlled by two sets of temperature controller. A mechanical pump was used to pump out the vapour of liquid nitrogen in the cryostat to solidify N₂ (1), and 60 K or even lower temperature was obtained. The performance of this apparatus was evaluated by heat capacity measurements on α-alumina. The deviations of experimental results from a smoothed curve lie within ±0.2%, while the inaccuracy is within ±0.5% compared with the recommended reference data in the wole temperature range.     

Heat capacity of poly(vinyl methyl ether)

The heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (?25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ₁ = 647 K, Θ₂ = Θ₃ = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by C_p(liquid) = 72.36 + 0.136 T in J K^?1 mol^?1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing C_p of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005     

Evaluation of the Compatibility of EPDM and IIR I. Specific heat capacity

The thermal effect of mixing of EPDM and IIR was studied by differential scanning calorimetry over the temperature range between 335 and 435 K. O'Neill's method was used for calculating the specific heat capacity with alumina as standard. The greater the butyl rubber content, the lower the heat capacity. The presence of butyl rubber induces a marked thermal instability because of isobutylene units. It is possible that a rearrangement occurs in the molecular sequence, accompanied by secondary reactions involving free radicals. The contribution of each component to the cP of the tested polymeric systems is discussed. Differences between theoretical and experimental specific heat capacities increase as the operation temperature is raised. The relationship between the contributions of the two components to the specific heat capacity values of mixtures can be described by a first order equation, named the law of reciprocal thermal affinity. This aspect can be ascribed to the interaction of various reacting entities, which form certain units with low molar heat capacity. This revised version was published online in July 2006 with corrections to the Cover Date.     

2-碘-3-硝基甲苯的低温热容和热力学性质

通过精密自动绝热热量计测定了2-碘-3-硝基甲苯(C~7H~6INO~2)在79～373K温区的摩尔热容。实验结果表明,这个化合物在331～340K温度区间有一个固-液熔化相变,其熔化温度、摩尔熔化焓、摩尔熔化熵以及该样品的化学纯度分别为：(339.311±0.13)J·mol^-^1·K^-^1和99.73%。用热容多项式议程进行数值积分获得了该物质在298.15～370K温区每隔5K的热力学函数值。用DSC分析对它的固-液相变过程作了进一步的研究。     

Volume and heat capacity studies to evidence interactions between cyclodextrins and nicotinic acid in water

Density and heat capacity of the water+cyclodextrin (CD), water+nicotinic acid (NA) and water+CD+NA mixtures were determined at 298.15 K. CDs with different cavity size and alkylation were selected. From the experimental data the apparent molar properties were calculated. Assuming the formation of inclusion complexes of 1:1 stoichiometry, these properties were modeled and provided the stability constants of CD/NA inclusion complexes and the corresponding property change. The binding of NA with the smallest sized α-cyclodextrin (α-CD) generates more stable complexes accompanied by the lower volume and the heat capacity changes. These results are in agreement with earlier proposed binding mode according to which deep insertion of NA into α-CD takes place and it is governed by the hydrophobic-hydrophilic forces. The volume and the heat capacity changes caused by the interactions of CDs with NA were interpreted in terms of cosphere overlap model and the release of water molecules from the CD cavity due to the NA incorporation.     

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.     

Dynamic disorder in the crystal structure of an organic semiconductor: an unusual phase transition involving the heat capacity

(E,E)-1-[2-(4-Nitrophenyl)ethenyl]-4-[2-(2,4-dimethoxyphenyl)ethenyl]benzene was characterised by X-ray diffraction and shown to be dynamically disordered at room temperature. The structure was re-determined over a range of temperatures to infer the thermodynamic parameters related to this disorder. A phase transition of third order according to the Ehrenfest classification scheme was discovered. To the best of our knowledge, this is the first experimentally observed phase transition of formal third order. It can be explained by the involvement of long-range lattice vibrations.     

Two-phase coexisting state of n-hexatriacontane in the first-order phase transition

The small crystal of n-hexatriacontane was observed by a polarizing microscope in the rotator phase transition temperature region. In the temperature region, the rotator phase coexists with the solid phase (low-temperature ordered phase). The boundaries of two phases move reversibly with the temperature change. The area fractional change of the rotator phase can be described by the Debye relaxation. The relaxation time decreases and the relaxation strength increases as the sample temperature is raised. The relaxation time agrees well with that of the dynamic specific heat, which was measured in the frequency range of 0.0003≤f/Hz≤0.05.     

Catabolic capacity of Saccharomyces cerevisiae in relation to the physiological state and maintenance requirement

The importance of the physiological state for the catabolic capacity during carbon- and energy-starving conditions was studied. Endogenous metabolism was low in cells depleted of carbon and energy source. This does not necessarily mean that these cells do not have the capacity for a higher catabolic activity. To measure the catabolic capacity of starved cells, carbon- and energy-depleted cells were suspended in synthetic fresh water and the respiratory and fermentative rates were examined after addition of glucose. The catabolic capacity was studied in cells of different physiological states. Stationary phase cells, which were depleted of their carbon and energy source for 6 h, showed a lower respiratory capacity, but almost as high a fermentative capacity as cells originating from the logarithmic phase of growth on glucose. With extended starvation time of stationary phase cells, the fermentative capacity decreased, while the respiratory capacity increased. Transition phase cells, characterised by a metabolic shift from a mixed respiratory-fermentative catabolism to a purely respiratory catabolism, showed, when newly harvested, a lower fermentative capacity than log phase cells with a mixed respiratory-fermentative catabolism. However, the fermentative capacity decreased during starvation of carbon and energy source for log phase cells, whereas transition phase cells increased the fermentative capacity to the same level as that of newly harvested log phase cells after 4 days without carbon or energy source.

The addition of glucose to stationary phase cells under non-growth conditions (no nitrogen source) resulted in ATP production rates of between 50% and almost 100% of the ATP produced by newly harvested log phase cells under the same conditions. Much higher rates of ATP production were attained for these different types of physiological states than can be explained by maintenance energy requirements. The suggested explanation for this over-consumption of energy during non-growth conditions in response to energy excess is metabolic uncoupling. This behaviour is discussed in relation to maintenance energy requirements during different environmental conditions.     

Enthalpy and heat capacity parameters of ammonium bromide interaction with hexamethylphosphotriamide in water

Thermal effects of solution of ammonium bromide in hexamethylphosphotriamide (HMPT)-water mixtures at 4° C, 15°C, and 46°C in the region of minor additions of the nonaqueous component were investigated for the first time by calorimetry. Variations of heat capacity in the course of solution were calculated using previous data for 25°C and 40°C. The curves of the heat capacity of solution (transfer) and temperature variation of transfer entropy versus composition have a minimum near the region of the existence of the 1:20 HMPT:water clathrate. The enthalpy, heat capacity, and temperature variations of the entropy coefficients of electrolyte amide pair and three-particle interactions in water were calculated in terms of MacMillan-Mayer theory. Within the framework of the group additivity method it is shown that the heat capacity coefficient of the bromide ion-HMPT pair interaction is negative and dictates temperature variations of enthalpy for ammonium bromide and tetraalkylammonium interactions with HMPT in water.     

Thermal expansivity,volume and the effect of pressure on the isobaric heat capacity of 1-hexanamine-1 hexanol mixtures from 0.1 to 400 MPa at 303 K up to 453 K

Thermal expansivities of liquid mixtures of 1-hexanol and 1-hexanamine have been determined as a function of pressure up to 400 MPa over the temperature range from 303 to 453 K. Measurements were performed in a pressure-scanning calorimeter by the stepwise technique. Compressibilities of the mixtures under study were determined at 303 K using the technique described before. Molar volumes under atmospheric pressure were determined for each mixture from the density measurements with a Paar instrument. From both the molar volume as a function of pressure at 303 K and the thermal expansivities the effects of pressure on the isobaric heat capacity were determined over the whole pressure and temperature range under study.

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Zusammenfassung Im Temperaturbereich 303–453 K wurde der thermische Ausdehungskoeffizient flüssiger Gemische aus 1-Hexanol und 1-Aminohexan als Funktion des Druckes bis 400 MPa bestimmt. Die Messungen wurden in einem Druck-Scanningkalorimeter nach der Schritt-für-Schritt-Methode ausgeführt. Die Kompressibilität der untersuchten Gemische wurde bei 303 K mittels der bereits beschriebenen Methode bestimmt. Mittels Dichtemessungen in einem Paar-Gerät wurde für jedes Gemisch das molare Volumen bei Atmosphärendruck ermittelt. Anhand der Druckabhängigkeit des molaren Volumens bei 303 K sowie der thermischen Ausdehnungskoeffizienten wurde der Einflu\ des Druckes auf die isobare Wärmekapazität im gesamten untersuchten Druck- und Temperaturintervall bestimmt.