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Abstract  

For complex heat capacity measurements, steady state of various types of temperature modulated DSC is theoretically investigated by a set of common comprehensive fundamental equations of heat balance. Heat capacities of heat paths, heat loss to the environment and mutual heat exchange between the sample and the reference material are taken into accounts together with thermal contact effect between the cell and its holder plate. Rigorous and general solutions have been obtained, and useful relations for complex heat capacity measurements have been derived for each type of DSC. They are compared with each other to elucidate unique features of each type of DSC.

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Abstract  

Complex heat capacity, C p *=C p 'iC p '', of lithium borate glasses xLi2O(1–x)B2O3 (molar fraction x=0.00–0.30) has been investigated by Modulated DSC. We have analyzed the shape of C p * by the Cole-Cole plot, performed fitting by the Havriliak-Negami equation, and then determined the parameters related to the non-Debye nature of thermal relaxation. Moreover, the concentration dependence of the thermal properties has been investigated. Glass transition temperatures become higher with the increase of molar fraction of Li2O and shows the board peak around x=0.26. Temperature ranges of glass transitions become narrower with the increase of Li2O concentration.

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Abstract  

To treat data from temperature modulated differential scanning calorimetry (TMDSC) in terms of complex or reversing heat capacity firstly one should pay attention that the response is linear and stationary because this is a prerequisite for data evaluation. The reason for non-linear and non-stationary thermal response is discussed and its influence on complex (reversing) heat capacity determination is shown. The criterion for linear and stationary response is proposed. This allows to choose correct experimental conditions for any complex heat capacity measurement. In the case when these conditions can not be fulfilled because of experimental restrictions one can estimate the influence of non-linearity and non-stationarity on measured value of complex or reversing heat capacity.

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Abstract  

Light heating dynamic DSC was used to study the melting transition of polyethylene. The results show that melting and crystallization are different phenomena from each other in terms of the complex heat capacity. Frequency dependence of the complex heat capacity was examined from 0.01 Hz to 0.2 Hz. It is found that at the lowest frequency the phase of the complex heat capacity exceeds π/2 radians. Thermodynamic considerations were made for the large phase of the complex heat capacity.

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Abstract  

An analysis developed in previous work has been further refined in order to study the effect of heat transfer on the heat capacity and phase angle measurements by TMDSC. In the present model, a temperature gradient within the sample has been taken into account by allowing for heat transfer by thermal conduction within the sample. The influence of the properties of the sensors, the heat transfer conditions between the sensor and sample,and the properties of the sample have been investigated by varying each parameter in turn. The results show that heat capacity measurements are reliable only within a restricted frequency range, for which the experimental conditions are such that the heat transfer phase angle depends linearly on the modulation frequency.

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detailed theory and calculation of complex heat capacity, reversing and non-reversing heat flow are discussed elsewhere [ 39 – 42 ]. Experimental The bio-based resin used in the present study was a commercial epoxidized

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Abstract  

The non-equilibrium process due to irreversible heat exchanges occurring during a temperature modulated differential scanning calorimetry (TMDSC) experiment is investigated in detail. This enables us to define an experimental frequency dependent complex heat capacity from this calorimetric method. The physical meaning of this dynamic heat capacity is discussed. A relationship is clearly established between the imaginary part of this complex quantity and the net entropy created during the experimental time-scale.

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Abstract  

The response of a chemical reaction to temperature modulation has been examined experimentally in an epoxy thermosetting system. The kinetic response appears in the imaginary part of the complex heat capacity determined by TMDSC. From the imaginary part and the ‘non-reversing’ heat flow of reaction, the activation energy has been determined. The value of the activation energy obtained is in good agreement with the value determined from Kissinger's plot utilizing the peak temperatures of the exothermic reaction with different heating rates.

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