Apparent Heat Capacities Research Articles

Heat capacity of six glymes in N,N-dimethylformamide + water mixtures. Solvation of glymes

The paper presents the heat capacities of glyme solutions: monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme, in binary solvents N,N-dimethylformamide + water at four temperatures (293.15 K, 298.15 K, 303.15 K, 308.15 K) obtained using differential calorimeter Micro DSC III, Setaram – France. The concentration of glymes was approximately 0.25 mol/kg. On the basis of the obtained experimental results, the apparent isobaric heat capacities of the glymes were calculated. It was noted that the larger the glyme molecule was, the more pronounced the increase in the value of the apparent molar heat capacity function with the increase in water content in the two-component solvent. The observed changes in apparent isobaric heat capacity as a function of the water content in the mixed solvent are discussed in terms of the hydrophobic nature of the glymes. Moreover, it was shown that the apparent molar isobaric heat capacity of the glymes in pure solvents, i.e. in water and in N,N-dimethylformamide, increases linearly with the increase in the number of oxygen atoms in the glyme molecules i.e. with the size of glyme molecules. Furthermore, a linear correlation was observed between the apparent isobaric molar heat capacity and the enthalpic effect of the hydrophobic hydration of the studied glymes at 298.15 K. The results obtained in this paper are compare with the same obtained for selected cyclic ethers.

Hidden Conformational States and Strange Temperature Optima in Enzyme Catalysis.

The existence of temperature optima in enzyme catalysis that occur before protein melting sets in can be described by different types of kinetic models. Such optima cause distinctly curved Arrhenius plots and have, for example, been observed in several cold-adapted enzymes from psychrophilic species. The two main explanations proposed for this behavior either invoke conformational equilibria with inactive substrate-bound states or postulate differences in heat capacity between the reactant and transition states. Herein, we analyze the implications of the different types of kinetic models in terms of apparent activation enthalpies, entropies, and heat capacities, using the catalytic reaction of a cold-adapted α-amylase as a prototypic example. We show that the behavior of these thermodynamic activation parameters is fundamentally different between equilibrium and heat capacity models, and in the α-amylase case, computer simulations have shown the former model to be correct. A few other enzyme-catalyzed reactions are also discussed in this context.

Generalized Quasi-Random Lattice model for electrolyte solutions: Apparent and partial molal heat capacities

Ionic solutions play an important role in many areas of technology and science, therefore understanding and predicting their thermodynamic behavior has been an essential research topic for an extended period of time. However, complexity and variety of real systems and the need for accurate representation of thermodynamic data hamper the development of models that are truly predictive over wide ranges of concentration, temperature and pressure conditions. In this regard, predictive potentialities of the Quasi-Random Lattice (QRL) model seem worthy of consideration.The QRL model, originally proposed for mean-activity/osmotic coefficients, was recently presented in a generalized form inclusive of formulae for partial/apparent molal enthalpies and volumes. This article follows and presents some further developments concerning partial and apparent molal heat capacities with application to various aqueous 1:1, 2:1, and 3:1 electrolytes. The semi-predictive character of QRL will be confirmed by present results and an improved procedure that yields the main QRL parameterization within a few steps will be illustrated. As a general remark, the experimental information required by QRL is very modest compared to the number of data points typically used with regression analysis.

Isobaric Heat Capacity of Ionic Liquids in Aqueous Solutions. A Review

A review of the available literature data for heat capacity of room temperature ionic liquid aqueous solutions is presented. To show at what extent their behavior departs from that of the ideal mixture, excess and apparent heat capacities are calculated. A comparison between different systems is made in order to elucidate the main factors that affect heat capacity behavior. The experimental results are also compared with available heat capacity data for salts and molecular compounds. Large deviations from ideality appear at low ionic liquid mole fraction. It is found that this nonideal behavior resembles, for most studied systems, that of molecular systems characterized by large hydrophobic domains. The appearance of pseudomicellar structures in diluted ionic liquid solutions seems to be the origin of the anomalies in the behavior of heat capacity.

Properties of Micellar Solutions of Sodium Decyl Sulfate at Relatively High Concentrations

Heat capacities of aqueous solutions of anionic surfactant sodium decyl sulfate in the 0.28–0.42 mol kg−1 range of molar concentrations and the 278–363 K range of temperatures are studied via precision adiabatic differential scanning microcalorimetry. Specific and apparent heat capacities of solutions at intervals of 0.01 mol kg−1, partial molar heat capacities of the solute and the solvent, and excess partial molar heat capacities are plotted as functions of concentration and temperature. The Kraft boundary is determined. Analysis of the characteristic changes in the above properties reveals structural changes in sodium decyl sulfate micelles that correspond to their shape transforming from cylindrical to plate-like in the region of the third critical micelle concentration.

Experimental investigation of thermal performance of microencapsulated PCM-contained wallboard by two measurement modes

Phase change materials (PCM) as a smart, feasible latent heat storage material has been utilized to reduce the energy demand and improve the thermal comfort of the buildings when incorporated into the building materials. Conventionally, the thermal behavior of the PCM mixed with the solid matrix (mortar or gypsum) is different with the bulk PCM. In this study, we designed an experimental apparatus to characterize the thermal performance of PCMs when they were utilized in their implementation state. Firstly, we investigated the effective thermal conductivity (λ) and the apparent specific heat (Cp) of the PCM-contained wallboard and the common gypsum wallboard, which were dependent on the temperature variation. Dynamic method was used to determine the phase change temperature, and the phase change process of the PCMs-wallboard was studied. Then, an “analogous step method” was proposed to determine the H(t) curves of the PCMs-wallboard, and the results were compared with the dynamic method. Finally, three methods of obtaining H(t) curves were compared and analyzed. From the obtained results, it can be concluded that when adopting the dynamic method appropriate heating rate (according to real application scenario) is necessary. When selecting the analogous step method, reducing the temperature interval can increase the accuracy of the H(t) even though it takes a lot of time. Anyway, both ways are more suitable for real wallboard test, comparing with the theoretical calculation method. The goal of our work is to investigate an appropriate method to evaluate the conductivities, apparent heat capacities, H(t) curves, and the phase change temperature of PCM-contained wallboards in their real application.

A study of the heat capacity of coated metal materials by the laser flash method

Results of laser-flash measurements of the specific heat capacity of samples of metallic materials (12Kh18N9T stainless steel, VZhM-4 nickel superalloy) coated with heat-resistant silicate enamel in a temperature range of 20–1300°C are described. In this temperature range, the coating is characterized by a high emissivity factor with a constant magnitude of 0.9. Analysis of the measurement results for the specific heat capacity of the steel samples and comparison of these results with the reference data and the most reliable literature data reveal that a decrease in the apparent specific heat capacity in a temperature range of 850–1100°C is attributed to an exothermic heat effect. The deviation of the measurement results from the reference data is no more than 3%. New data on the heat capacity of the VZhM-4 nickel alloy are derived. The temperature dependences of the apparent (with allowance for the heat effect of dissolution of the γ' phase) and true specific heat capacities are described. The discrepancy between the calculated and measured values does not exceed 2%.

Volumetric and calorimetric properties of aqueous ionene solutions

The volumetric (partial and apparent molar volumes) and calorimetric properties (apparent heat capacities) of aqueous cationic polyelectrolyte solutions - ionenes - were studied using the oscillating tube densitometer and differential scanning calorimeter. The polyion's charge density and the counterion properties were considered as variables. The special attention was put to evaluate the contribution of electrostatic and hydrophobic effects to the properties studied. The contribution of the CH2 group of the polyion's backbone to molar volumes and heat capacities was estimated. Synergistic effect between polyion and counterions was found.

On the link between conformational changes, ligand binding and heat capacity

BackgroundConformational changes coupled to ligand binding constitute the structural and energetics basis underlying cooperativity, allostery and, in general, protein regulation. These conformational rearrangements are associated with heat capacity changes. ITC is a unique technique for studying binding interactions because of the simultaneous determination of the binding affinity and enthalpy, and for providing the best estimates of binding heat capacity changes. Scope of reviewStill controversial issues in ligand binding are the discrimination between the “conformational selection model” and the “induced fit model”, and whether or not conformational changes lead to temperature dependent apparent binding heat capacities. The assessment of conformational changes associated with ligand binding by ITC is discussed. In addition, the “conformational selection” and “induced fit” models are reconciled, and discussed within the context of intrinsically (partially) unstructured proteins. Major conclusionsConformational equilibrium is a major contribution to binding heat capacity changes. A simple model may explain both conformational selection and induced fit scenarios. A temperature-independent binding heat capacity does not necessarily indicate absence of conformational changes upon ligand binding. ITC provides information on the energetics of conformational changes associated with ligand binding (and other possible additional coupled equilibria). General significancePreferential ligand binding to certain protein states leads to an equilibrium shift that is reflected in the coupling between ligand binding and additional equilibria. This represents the structural/energetic basis of the widespread dependence of ligand binding parameters on temperature, as well as pH, ionic strength and the concentration of other chemical species. This article is part of a Special Issue entitled Microcalorimetry in the BioSciences — Principles and Applications, edited by Fadi Bou-Abdallah.

Thermal properties of non-crystallizable oil-in-water highly concentrated emulsions

In this work, a differential-scanning-calorimetry (DSC) technique is applied to studying the thermal properties of highly concentrated oil-in-water (O/W) emulsions of two immiscible liquids (castor oil and water) with high viscosity ratios (3400/1 for O/W), similar densities (0.974/1 for O/W) and stabilized by a non-ionic surfactant. A low-energy mixing process was used to produce highly concentrated emulsions (typically more than 90% O/W) with different mean droplet sizes, dependent on the emulsification time. The oil is non-crystallizable, thus only very thin water-surfactant films and water-surfactant solutions at the Plateau border and node regions between the compressed oil droplets crystallize under freezing. We show that the DSC technique is able to reveal the influence of interfacial energy phenomena (i.e., surface-to-volume effects) on the supercooling degree and on the apparent specific heat capacities of the concentrated emulsions.

Thermodynamique des systèmes micellaires Partie III : Capacités calorifiques apparente et partielle des alcanoates de sodium

Thermodynamics of micellar systems Part III : Apparent and partial heat capacities of sodium alkanoates To obtain the heat capacities of the aqueous solutions of the sodium carboxylates, we carry out microcalorimetric heat capacities measurements. The aim of this work is to calculate the quantities of the apparent and partial molar heat capacities, and also to define the critical micellar concentrations. The variations of the partial molar heat capacities by increment -CH2 allows us to give prove for products supposed to form true micelles and products do not form micelles. To discuss the solute-solvent and solutesolute interactions we used the standard apparent molar heat capacities.

Thermodynamics of aqueous L-proline solutions at 273–323 K

Enthalpies of dissolution of L-proline in water were measured calorimetrically at 283–313 K. The experimental temperature of dissolution of proline in water at the studied temperatures was shown to be almost independent of its concentration over the range 0.01–0.11 mol/kg. Standard enthalpies of dissolution and standard heat capacities of dissolution were calculated over this temperature range. The heat capacity of dissolution was ascertained to increase in the row glycine, proline, and alanine. The partial molar heat capacity of proline in water was determined and compared with the values obtained by extrapolation of the apparent heat capacities. The changes in entropy and reduced enthalpy and the Gibbs energy over the temperature range from 273 to 323 K were determined using familiar thermodynamic relations. The data for glycine and alanine were compared.

Component heat capacities for lamb, beef and pork at elevated temperatures

The design of cooking and cooling processes requires knowledge of the thermal properties of the food product. The heat capacity of food may be estimated by summing the apparent heat capacities of its components. This paper reports the apparent heat capacities of protein and fat components from lamb, beef and pork measured by a differential scanning calorimeter over the temperature range 30–85 °C. These measurements extend the range of available heat capacity data for individual components of meats.

Thermal properties of aliphatic nylons and their link to crystal structure and molecular motion

The phase behavior of semicrystalline, aliphatic nylons is analyzed on the basis of differential scanning calorimetry, DSC, and quasi-isothermal, temperature-modulated DSC, TMDSC. The data of main interest are the apparent heat capacities, Cp, in the temperature range from below the glass transitions to above the isotropization. Based on the contributions of the vibrational motion to Cp, as is available from measurements in our laboratory, the ATHAS Data Bank, and multifaceted new TMDSC results, as well as on information on the crystal structures, NMR, molecular dynamics simulation of paraffin crystals, and quasi-elastic neutron scattering, the following observations are made: (a) In semicrystalline nylons the glass transition of the mobile-amorphous phase is broadened to higher temperature. The additionally present rigid-amorphous phase, RAF, undergoes a separate, broad glass transition at somewhat higher temperature. (b) The transition of the RAF, in turn, overlaps usually with an increase in large-amplitude motion of the CH2-groups within the crystals and latent heat effects due to melting, recrystallization, and crystal annealing. (c) Above the glass transitions of the two non-crystalline phases, Cp of the crystals approaches and exceeds that of the melt. This effect is due to additional entropy contributions (disordering) within the crystals, which may for some nylons lead to a mesophase. In case a mesophase is formed, the Cp drops to the level of the melt as is common for mesophases. (d) Some locally reversible melting is present on the crystal surfaces, but seems to be minimal for the mesophase. (e) The increasing amount of large-amplitude motion in the crystals is described as a third glass transition, occurring over a broad temperature range below the melting or disordering transition from crystal to mesophase.

Origin of heat capacity changes in a "nonclassical" hydrophobic interaction.

Origin of heat capacity changes in a "nonclassical" hydrophobic interaction.

Apparent Specific Heat Capacity of Chilled and Frozen Meat Products

In this article, apparent specific heat capacities of meat and meat products, minced beef, hamburger patties, soudjouk, minced turkey meat, turkey sausage, and turkey soudjouk, were measured at temperatures ranging from −60°C to +40°C, using a differential scanning calorimeter. Experimental data were compared with values calculated from different predictive models given in the literature. Measured apparent specific heat capacities were also mathematically interpreted as a function of temperature, moisture and fat content by application of nonlinear regression analysis for frozen and unfrozen samples. The developed models were found to be in good agreement with the experimental data.

Reversing and Nonreversing Heat Capacity of Poly(lactic acid) in the Glass Transition Region by TMDSC

A study of the glass transition of an amorphous and a semicrystalline poly(lactic acid) (PLA) is performed with adiabatic calorimetry, differential scanning calorimetry (DSC), and temperature-modulated DSC (TMDSC). The reversing, total, and nonreversing apparent heat capacities of samples with different contents of l- and d-lactic acid and with various thermal histories were evaluated. Different modes of TMDSC analyses of amorphous and semicrystalline PLA were compared to the total heat capacity from standard DSC. The enthalpy relaxation and the cold crystallization in the glass transition region are largely irreversible. The melting is largely irreversible, but a 100% reversing fraction is observed at low temperatures from 375 to 420 K, which becomes small inside the major melting peak at about 440 K. From the TMDSC of amorphous PLA, the combined information on endothermic and exothermic enthalpy relaxation and glass transition were deconvoluted into the reversing and nonreversing components. The glass t...

Properties of composite materials for thermal analysis involving fires

Inverse heat transfer analysis was used to determine thermal and physical properties of a coupon size glass reinforced vinyl ester composite sample from ambient to 800 °C. The decomposition of the coupon sample was measured to occur over the same temperature range as measured for fragment and powder samples in a thermogravimetric analyzer (TGA); however, the rate of change in mass was different resulting in different Arrhenius decomposition kinetic parameters. The specific heat capacity determined using a coupon sample was 15% higher than that measured in the differential scanning calorimeter (DSC). The apparent specific heat capacity, which includes the sensible and latent portions of the heat capacity, was calculated from the coupon sample data as well as the TGA and DSC data. These apparent specific heat capacities were input into a transient heat conduction model to predict the temperature profile through a sample. Though different apparent specific heat capacities were calculated, all model predictions were within 10% of the data.

Asphaltene phase behavior: prediction at a crossroads

Recent results from SAXS, X-ray transmission, and differential scanning and other calorimetry experiments with neat asphaltenes and asphaltene + hydrocarbon mixtures highlight the structural and behavioral complexity of asphaltenes, however defined, at diverse length scales. Much of this complexity spans the temperature range of importance for reservoir fluid applications, and calls into question many aspects of existing thermodynamic models for them. Apparent heat capacities, for neat asphaltenes, can drop below those of rigid organic crystals revealing the presence of significant exotherms. Of equal importance, typical molecular and submolecular analysis techniques: C13NMR, fluorescence, elemental analysis, ‘molar mass’ do not appear to correlate with asphaltene behaviors in their native oils or in solvent solutions at infinite dilution. Maya and athabasca asphaltenes provide an excellent illustration of this phenomenon. Our understanding of the phase behavior of neat asphaltenes and the behavior of asphaltenes in fluids is at a crossroads.

Apparent molar heat capacities and apparent molar volumes of Pr(ClO 4) 3(aq), Gd(ClO 4) 3(aq), Ho(ClO 4) 3(aq), and Tm(ClO 4) 3(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa

Acidified aqueous solutions of Pr(ClO 4) 3(aq), Gd(ClO 4) 3(aq), Ho(ClO 4) 3(aq), and Tm(ClO 4) 3(aq) were prepared from the corresponding oxides by dissolution in dilute perchloric acid. Once characterized with respect to trivalent metal cation and acid content, the relative densities of the solutions were measured at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa using a Sodev O2D vibrating tube densimeter. The relative massic heat capacities of the aqueous systems were also determined, under the same temperature and pressure conditions, using a Picker Flow Microcalorimeter. All measurements were made on solutions containing rare earth salt in the concentration range 0.01 ⩽ m/(mol · kg −1) ⩽ 0.2. Relative densities and relative massic heat capacities were used to calculate the apparent molar volumes and apparent molar heat capacities of the acidified salt solutions from which the apparent molar properties of the aqueous salt solutions were extracted by the application of Young's Rule. The concentration dependences of the isothermal apparent molar volumes and heat capacities of each aqueous salt solution were modelled using Pitzer ion-interaction equations. These models produced estimates of apparent molar volumes and apparent molar heat capacities at infinite dilution for each set of isothermal V φ,2 and C p φ,2 values. In addition, the temperature and concentration dependences of the apparent molar volumes and apparent molar heat capacities of the aqueous rare earth perchlorate salt solutions were modelled using modified Pitzer ion-interaction equations. The latter equations utilized the Helgeson, Kirkham, and Flowers equations of state to model the temperature dependences (at p=0.1 MPa) of apparent molar volumes and apparent molar heat capacities at infinite dilution. The results of the latter models were compared to those previously published in the literature. Apparent molar volumes and apparent heat capacities at infinite dilution for the trivalent metal cations Pr 3+(aq), Gd 3+(aq), Ho 3+(aq), and Tm 3+(aq) were calculated using the conventions V 2 ∘(H +(aq)) ≡ 0 and C p2 ∘(H +(aq)) ≡ 0 and have been compared to other values reported in the literature.