Change In Specific Heat Capacity Research Articles

Thermal, Electrical, Microstructure and Microhardness Properties of the Eutectic Magnesium–Tin

The variation of thermal conductivity with temperature for Sn-2.0 wt.% Mg eutectic alloy was measured to be 68.29 ± 4.09 W/Km with a radial heat flow apparatus. The electrical conductivities of the sample were calculated the Wiedemann–Franz–Lorenz law, Smith–Palmer equation, Bungardt–Kallenbach and Powell empirical correlations by using the thermal conductivity value, respectively.The values of enthalpy of fusion (ΔH) and the change of specific heat capacity (ΔCp) were also obtained by differential scanning calorimeter (DSC), respectively. The microhardness value for the alloy was measured by Vickers microhardness device. The microstructure and composition of the alloy was investigated by using SEM and EDX analysis. According to the results, the defects which depending on composition and temperature could increase the electrical resistivity.

Wave propagation and thermodynamic losses in packed-bed thermal reservoirs for energy storage

This paper presents a numerical and theoretical analysis of thermal wave propagation in packed bed thermal reservoirs for energy storage applications. In such reservoirs, the range of temperatures encountered is usually such that the solid storage medium will exhibit significant changes in specific heat capacity. This in turn results in non-linear wave propagation and may lead to the formation of shock-like thermal fronts. Such effects have an impact on the exergetic losses due to irreversible heat transfer, and should be taken into account during the design and optimisation of the reservoirs. In the present paper, the emphasis is on thermal losses due to irreversible heat transfer. Frictional (pressure) losses and heat leakage between the storage medium and the environment are also important but are not considered here. The implications of the results for storage material, and particle size are discussed briefly in the context of loss minimisation.

Modeling differential scanning calorimetry of thermally degrading thermoplastics

Differential scanning calorimetry (DSC) of thermally degrading thermoplastics is modeled using a discrete population balance equation (PBE). The PBE allows for species mole change due to pyrolysis and bubbling mass loss. Efficient solution is achieved by lumping non-volatile species into a single, notional “polymer” species. Thermodynamic properties are calculated by group additivity techniques, and empirical corrections are made to account for the changes in specific heat capacity and enthalpy upon mixing. Simulation results for high-density polyethylene (HDPE) are compared to literature data for DSC at heating rates of 5, 10, and 20K/min. The model predicts peak energy absorption rates to within 4% at the lowest heating rate. The heat of decomposition was found to be within 17% of literature values at all three heating rates. The predicted pyrolysis gas species distribution agrees well with literature gas chromatography–mass spectrometry (GC–MS) data.

Effect of composition on the thermal behavior of NiMnGa alloys

The methods to determine martensitic transformation temperature, enthalpy and entropy change, specific heat capacity change with temperature, and transformation activation energies of Ni–%29.5Mn–%21Ga, Ni–%29Mn–%21Ga, Ni–%29.5Mn–%20Ga, and Ni–%28.5Mn–%20.5Ga (atomic percentage) alloys were investigated by differential scanning calorimetry. It was observed that the transformation temperature increased with an increase in atomic nickel ratio. Meanwhile, it was detected that the change in enthalpy increases with the amount of nickel. The highest values of entropy change and the heat capacity at room temperature were observed in the alloy having the least amount of nickel in it.

Effect of DNA groove binder distamycin A upon chromatin structure.

BackgroundDistamycin A is a prototype minor groove binder, which binds to B-form DNA, preferentially at A/T rich sites. Extensive work in the past few decades has characterized the binding at the level of double stranded DNA. However, effect of the same on physiological DNA, i.e. DNA complexed in chromatin, has not been well studied. Here we elucidate from a structural perspective, the interaction of distamycin with soluble chromatin, isolated from Sprague-Dawley rat.Methodology/Principal FindingsChromatin is a hierarchical assemblage of DNA and protein. Therefore, in order to characterize the interaction of the same with distamycin, we have classified the system into various levels, according to the requirements of the method adopted, and the information to be obtained. Isothermal titration calorimetry has been employed to characterize the binding at the levels of chromatin, chromatosome and chromosomal DNA. Thermodynamic parameters obtained thereof, identify enthalpy as the driving force for the association, with comparable binding affinity and free energy for chromatin and chromosomal DNA. Reaction enthalpies at different temperatures were utilized to evaluate the change in specific heat capacity (ΔCp), which, in turn, indicated a possible binding associated structural change. Ligand induced structural alterations have been monitored by two complementary methods - dynamic light scattering, and transmission electron microscopy. They indicate compaction of chromatin. Using transmission electron microscopy, we have visualized the effect of distamycin upon chromatin architecture at di- and trinucleosome levels. Our results elucidate the simultaneous involvement of linker bending and internucleosomal angle contraction in compaction process induced by distamycin.Conclusions/SignificanceWe summarize here, for the first time, the thermodynamic parameters for the interaction of distamycin with soluble chromatin, and elucidate its effect on chromatin architecture. The study provides insight into a ligand induced compaction phenomenon, and suggests new mechanisms of chromatin architectural alteration.

Calorimetric and spectroscopic studies of aminoglycoside binding to AT-rich DNA triple helices

Calorimetric and fluorescence techniques were used to characterize the binding of aminoglycosides-neomycin, paromomycin, and ribostamycin, with 5′-dA 12-x-dT 12-x-dT 12-3′ intramolecular DNA triplex (x = hexaethylene glycol) and poly(dA)·2poly(dT) triplex. Our results demonstrate the following features: (1) UV thermal analysis reveals that the T m for triplex decreases with increasing pH value in the presence of neomycin, while the T m for the duplex remains unchanged. (2) The binding affinity of neomycin decreases with increased pH, although there is an increase in observed binding enthalpy. (3) ITC studies conducted in two buffers (sodium cacodylate and MOPS) yield the number of protonated drug amino groups (Δn) as 0.29 and 0.40 for neomycin and paromomycin interaction with 5′-dA 12-x-dT 12-x-dT 12-3′, respectively. (4) The specific heat capacity change (Δ C p) determined by ITC studies is negative, with more negative values at lower salt concentrations. From 100 mM to 250 mM KCl, the Δ C p ranges from −402 to −60 cal/(mol K) for neomycin. At pH 5.5, a more positive Δ C p is observed, with a value of −98 cal/(mol K) at 100 mM KCl. Δ C p is not significantly affected by ionic strength. (5) Salt dependence studies reveal that there are at least three amino groups of neomycin participating in the electrostatic interactions with the triplex. (6) FID studies using thiazole orange were used to derive the AC 50 (aminoglycoside concentration needed to displace 50% of the dye from the triplex) values. Neomycin shows a seven fold higher affinity than paromomycin and eleven fold higher affinity than ribostamycin at pH 6.8. (7) Modeling studies, consistent with UV and ITC results, show the importance of an additional positive charge in triplex recognition by neomycin. The modeling and thermodynamic studies indicate that neomycin binding to the DNA triplex depends upon significant contributions from charge as well as shape complementarity of the drug to the DNA triplex Watson–Hoogsteen groove.

Evidence of an intermediate phase in ternary Ge7Se93-xSbx glasses

The compositional dependence of thermal properties, such as glass transition temperature (T-g), non-reversing enthalpy change (Delta H-NR) and the specific heat capacity change (Delta C-p) of melt quenched Ge7Se93-xSbx (21 a parts per thousand currency sign x a parts per thousand currency sign 31) glasses, has been studied using alternating differential scanning calorimetry (ADSC) which is analogous to modulated differential scanning calorimetry (MDSC). The glass transition temperature, T-g, which is a measure of global connectivity of the glass, has been found to increase with the addition of Sb. In addition, a change in slope has been observed in the composition dependence of T-g at an average coordination aOE (c) r > = 2.40. The experimentally observed compositional variation of glass transition temperature, has been compared with the theoretical predictions from the stochastic agglomeration theory (SAT) and has been found to be consistent. Further, a narrow thermally reversing window is seen in the compositional variation of the relaxation enthalpy (Delta H-NR), which is centered around aOE (c) r > = 2.40. The change in specific heat capacity (Delta C-p) at T-g is also found to exhibit a distinct minima at aOE (c) r > = 2.40, suggesting that the structural rearrangements for the liquid in the glass transition region are minimized around aOE (c) r > = 2.4.

Fire model for fibre reinforced plastic composites using apparent thermal diffusivity (ATD)

A new model has been developed for the prediction of thermal profiles for fibre reinforced plastic composites exposed to high one sided heat flux. The model involves expressing the thermal diffusivity of the composite as a function of temperature. Apparent thermal diffusivity (ATD) can take into account the decomposition of the resin, which is endothermic, as well as the consequent changes in specific heat capacity and thermal conductivity of the composite. This offers the possibility of significantly simplifying computational procedures needed for modelling thermal behaviour with decomposition. Temperature profiles were measured at different depths through the thickness of a chopped strand mat/polyester composite and compared with the results obtained with the ATD model. The results were also compared with predictions of the COM_FIRE model, a previously developed heat transfer model for fibre reinforced composites in fire, based on the Henderson equation.

Thermal unfolding of the archaeal DNA and RNA binding protein Ssh10

The reversible thermal unfolding of the archaeal histone-like protein Ssh10b from the extremophile Sulfolobus shibatae was studied using differential scanning calorimetry and circular dichroism spectroscopy. Analytical ultracentrifugation and gel filtration showed that Ssh10b is a stable dimer in the pH range 2.5–7.0. Thermal denaturation data fit into a two-state unfolding model, suggesting that the Ssh10 dimer unfolds as a single cooperative unit with a maximal melting temperature of 99.9°C and an enthalpy change of 134kcal/mol at pH 7.0. The heat capacity change upon unfolding determined from linear fits of the temperature dependence of ΔHcal is 2.55kcal/(molK). The low specific heat capacity change of 13cal/(molK residue) leads to a considerable flattening of the protein stability curve (ΔG (T)) and results in a maximal ΔG of only 9.5kcal/mol at 320K and a ΔG of only 6.0kcal/mol at the optimal growth temperature of Sulfolobus.

Thermal, electrical and magnetic studies of magnetite filled polyurethane shape memory polymers

Thermal, electrical and magnetic properties of polyurethane shape memory polymer (SMP) samples filled with 0–40 vol% magnetite particles prepared by mixing and injection molding were investigated. Shape recovery in the shape memory polymer was initiated by a magnetizing field of H = 4.4 kA/m at a frequency f = 50 Hz. Electric resistivity was decreased by magnetite particles from ρ el ≈ 10 10 Ω m to ρ el ≈ 10 6 Ω m. The percolation threshold is achieved at a magnetite concentration of approximately 30 vol%. Thermal conductivity increases from 0.19 W/m K to 0.60 W/m K with magnetite fraction in the polymer. Thermal conductivity values are compared with several theoretical and semi empirical models. The Agari–Uno model shows a very good correlation to measured values. Changes in specific heat capacity with temperature were also measured and could be correlated with the morphology of the polymer. With a hysteresis recorder the power losses in magnetization reversal of the filled SMP were estimated. Using measured specific heat capacity and power losses the time for an increase of sample temperature from room temperature up to shape recovery temperature was calculated to be t ≈ 4 min. Time dependent photographic pictures of the shape recovery process showed a good accordance between the calculated and observed time for the shape recovery.

Effect of network connectivity on thermal properties of As30Te70– x Tl x glasses

Alternating differential scanning calorimetry (ADSC) studies were undertaken to investigate the effect of Tl addition on the thermal properties of As30Te70– x Tl x (6 ≤ x ≤ 22 at%) glasses. These include parameters such as glass-transition temperature (T g), changes in specific heat capacity (ΔC p) and relaxation enthalpy (ΔH NR) at the glass transition. It was found that T g of the glasses decreased with the addition of Tl, which is in contrast to the dependence of T g in As–Te glasses on the addition of Al and In. The change in heat capacity ΔC p through the glass transition was also found to decrease with increasing Tl content. The addition of Tl to the As–Te matrix may lead to a breaking of As–Te chains and the formation of Tl+Te−AsTe2/2 dipoles. There was no significant dependence of the change of relaxation enthalpy, through the glass transition, with composition.

Predictors of glass transition in the biodegradable poly‐lactide and poly‐lactide‐co‐glycolide polymers

AbstractThe biodegradable polylactide (PLA) and polylactide‐co‐glycolides (PLGAs) are being widely investigated for use as scaffolds in bone and ligament reconstruction. The glass transition temperatures (Tg) for these polymers are generally greater than 37°C, causing PLA and PLGA devices to possess brittle characteristics in physiological conditions. To evaluate the possibility of obtaining PLGA polymers with Tg values below 37°C, we evaluated the determinants of Tg in PLA and PLGA copolymers. The Tg, changes in specific heat capacity (ΔCp), and enthalpic relaxation (ΔHg) in two consecutive heating cycles were correlated with lactide/glycolide content and intrinsic viscosity [η] for PLA, PLGAs 90:10, 75:25, 65:35, and 50:50. A linear correlation was observed between Tg and intrinsic viscosity, with 0.1 dL/g increase in viscosity resulting in an increase in Tg by about 3.55°C. The selection of PLA and PLGA copolymers with [η] values <0.19 dL/g, corresponding to a viscosity average molecular weight of <70 kDa, will obtain PLA/PLGA polymers with Tg values below 37°C. The lowest attainable Tg values were found to be 28–30°C. Intrinsic viscosity also correlated with ΔCp differences between aged and rapidly cooled polymers, and is therefore important in predicting free volume changes within these polymers upon aging. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1983–1987, 2006

A heat exchanger model that includes axial conduction, parasitic heat loads, and property variations

High performance heat exchangers are a critical component in many cryogenic systems and the performance of these devices is typically very sensitive to axial conduction, property variations, and parasitic heat losses to the environment. This paper presents a numerical model of a heat exchanger in which these effects are explicitly modeled. The governing equations are derived, nondimensionalized, discretized, and solved on an exponentially distributed grid. The resulting numerical model is simple to implement and computationally efficient and can therefore easily be integrated into complex system models. The numerical model is validated against analytical solutions in the appropriate limits and then used to investigate the effect of heat exchanger end conditions (adiabatic vs fixed temperature) and radiation parasitics. The numerical model, which explicitly considers the combined effect of several loss mechanisms as they interact, is compared to simple models that consider these effects separately. Finally, the model is applied to an example heat exchanger core under a specific set of operating conditions in order to demonstrate its utility. This numerical model may also be used to examine the effect of property variations including temperature driven changes in specific heat capacity, metal conductivity, parasitic heat load, and heat transfer coefficients and is therefore useful in the design of a variety of cryogenic system components including counter- and parallel-flow heat exchangers for gas liquefaction, mixed-gas refrigeration, and reverse Brayton systems.

Molecular-Level Thermodynamic Switch Controls Chemical Equilibrium in Sequence-Specific Hydrophobic Interaction of 35 Dipeptide Pairs

Applying the Planck-Benzinger methodology, the sequence-specific hydrophobic interactions of 35 dipeptide pairs were examined over a temperature range of 273–333 K, based on data reported by Nemethy and Scheraga in 1962. The hydrophobic interaction in these sequence-specific dipeptide pairs is highly similar in its thermodynamic behavior to that of other biological systems. The results imply that the negative Gibbs free energy change minimum at a well-defined stable temperature, 〈 T s〉, where the bound unavailable energy, TΔ S o = 0, has its origin in the sequence-specific hydrophobic interactions, are highly dependent on details of molecular structure. Each case confirms the existence of a thermodynamic molecular switch wherein a change of sign in Δ Cp o( T) reaction (change in specific heat capacity of reaction at constant pressure) leads to true negative minimum in the Gibbs free energy change of reaction, Δ G o( T) reaction, and hence a maximum in the related equilibrium constant, K eq. Indeed, all interacting biological systems examined to date by Chun using the Planck-Benzinger methodology have shown such a thermodynamic switch at the molecular level, suggesting its existence may be universal.

Thermodynamic molecular switch in micelles

It is well known that essentially all macromolecular interactions function over a well-defined temperature range. The Gibbs free energy change, Δ G °( T), for macromolecular interaction shows a complicated behavior, wherein Δ G °( T) changes from positive to negative, then reaches a negative value of maximum magnitude (favorable), and finally becomes positive as temperature increases. This communication demonstrates that the critical factor is a temperature-dependent Δ C p °( T) (specific heat capacity change) of reaction, which is positive at low temperature but switches to a negative value at a temperature well below the ambient range. This thermodynamic molecular switch determines the behavior patterns of the Gibbs free energy change, and hence a change in the equilibrium constant, K eq, and/or spontaneity. The subsequent, mathematically predictable changes in Δ H °( T), Δ S °( T), Δ W °( T) and Δ G °( T) give rise to the classically observed behavior patterns in biological systems. This communication will also demonstrate the existence of a thermodynamic molecular switch in both nonionic surfactants, (OPE) i where i=1, 3, 8, and 10 and ionic n-DTAB surfactants in H 2O, D 2O, 3 M urea and 2 M dioxane, over the experimental temperature range of 285–360 K, based on Chun's development of the Planck–Benzinger methodology (P.W. Chun, Int. J. Quantum Chem.: Quantum Biol. Symp. 15 (1988) 247; P.W. Chun, Manual for Computer-Aided Analysis of Biochemical Processes with Florida 1-2-4, University of Florida copyright reserved, 1991; P.W. Chun, J. Phys. Chem. 86 (1994) 6851; P.W. Chun, J. Biol. Chem., 270 (1995) 13925; P.W. Chun, J. Phys. Chem. 100 ( ̄ 1996) 7283; P.W. Chun, in: 212th National American Chemistry Society Meeting, Orlando, Fla, American Chemical Society, Biophysical Chemistry, poster 283, 1996; P.W. Chun, J. Phys. Chem. B 101 (1997) 7835; P.W. Chun, Methods in Enzymology, vol. 295, 1998, pp. 12, 227; P.W. Chun, Int. J. Quantum Chem.: Quantum Biol. Symp., 75 (1999) 1027; P.W. Chun, Int. J. Quantum Chem.: Quantum Biol. Symp. (2000); P.W. Chun, Biophysical J., 75 (2000) 416; P.W. Chun, Cell Biochem. Biophys. (2000)). In the case of micellar size distribution, the change in inherent chemical bond energy, ΔH °( T 0), in micellar interaction is small. In contrast, the thermal agitation energy (heat capacity integrals), is much larger and roughly the same over a broad size distribution. This qualitative trend differs markedly from results seen for biochemical interactions, yet the underlying mathematical interpretation is the same.

Influence of the structure of soft and stiff chain fragments on properties of segmented polyurethanes. I. Phase morphology

AbstractModel segmented polyurethanes (SPUs) prepared from either oxypropylene glycol oligomer or butylene adipate glycol oligomer, both of molar mass 2 kg/mol (soft fragments, SFT), and three different diisocyanates (all‐trans 4,4'‐dicyclohexylmethane diisocyanate, t, t‐HMDI‐1.0; HMDI with 20% of trans isomers, t, t‐HMDI‐0.2; and 4, 4'‐diphenylmethane diisocyanate, MDI) (stiff fragments, STF) were characterized by specific heat capacity measurements in the temperature interval 140‐540 K, and by wide‐angle and small‐angle X‐ray scattering at room temperature. Limited miscibility of SFT and STF chain components resulted in incomplete separation into a regular three‐dimensional macrolattice of STF‐rich microdomains and SFT‐rich microphases. The composition of STF‐rich microdomains was estimated by fitting the softening temperatures to the Couchman's equation, whereas the relative contents of SFT‐rich and STF‐rich microphases were assessed by comparing the specific heat capacity change at the glass transition temperatures to corresponding additive values. The overall degree of microphase separation, as well as the mean macrolattice spacings between STF microdomains decreased in the order, MDI > t, t‐HMDI‐1.0 ≫ t, t‐HMDI‐0.2. The conformation of STF fragments within the STF‐rich microdomains changed from nearly extended (for MDI) through slightly contracted (for t, t‐HMDI‐1.0) to strongly contracted (for t, t‐HMDI‐0.2).

DSC studies on specific heat capacity of irradiated ethylene-propylene elastomers—II. EPDM

Changes in the specific heat capacity of ethylene-propylene-diene terpolymer (EPDM) containing 3.5% ENB were investigated over a temperature range from 340 up to 440 K. Exposure to gamma radiation was carried out at various doses up to 600 kGy. Evaluation of c p was done using O'Neill's method with aluminia as standard. Specific heat capacity of EPDM changed differently if irradiation was performed in air or in vacuum. The shape of c p = F( T) curves depends on the competition of scission and crosslinking and on later reactions involving long life radicals. Radiation resistance of EPDM can be evaluated by determination of change in specific heat capacity.

Lithium borate glasses: a quantitative study of strength and fragility

Methods for quantifying the strength/fragility of glass-forming systems are described, with particular reference to the alkali borates. One parameter used is the limiting slope of the log viscosity versus T ∗/T plot as T approaches T ∗ , the temperature at which the viscosity is 10 12 Pa s. A comparison is made with ΔC p / C p1 , the normalised change in specific heat capacity at T g, as an alternative measure of the degree of fragility in these glass-forming systems. Both approaches indicate that increasing alkali oxide content results in increasing fragility within the borate system, although anomalous correlations can result when different glassy system are compared. The extent to which the limiting viscosity slope and ΔC p / C p1 probe different aspects of structural change and fragility is briefly explored.

Calorimetric and circular dichroic studies of the thermal denaturation of beta-lactoglobulin.

The thermal denaturation of beta-lactoglobulin in aqueous solutions at pH 5.5 and 2.0 was investigated by differential scanning calorimetry (DSC) and circular dichroic (CD) measurements. By calorimetry, the denaturation temperatures (Td), denaturation enthalpies, and specific heat capacity changes for thermal denaturation in the temperature range scanned, i.e., 20-100 degrees C. The unfolding process was found to be only partially reversible. Analysis of the far-ultraviolet CD spectra reveals that with increasing temperature the mean residue ellipticity [( theta]) becomes less negative, which reflects unfolding of the native protein. At the highest temperature of CD measurements, i.e., 80 degrees C, conformational changes are to a large extent reversible.

Changes of specific heat capacity and heat capacity during weathering

An approach is presented which must be followed in the study of a deep-weathering profile. The present research pursues the evaluation of changes in specific heat capacity and heat capacity during weathering. For the first step to obtain the values of specific heat capacity and heat capacity in practical use, the mutual relationships among vertical changes in various kinds of rock properties are investigated in a weathering profile of granite. Two derivable formulas for estimating the values of specific heat capacity and volumetric heat capacity in weathered rock have been theoretically derived from the values of some properties. The changes of specific heat capacity and volumetric heat capacity in rock during natural weathering are also evaluated on the basis of the available data of physical properties.