Scanning transitiometry

The importance of temperature-controlled scanning calorimetry for measurements of heat capacity and of scanning transitiometry for simultaneous caloric and pVT analysis has been demonstrated for polymorphic systems [9]. This approach was used to study an enantiotropic system characterized by multiphase (and hindered) transitions, the role of heat capacity as a means to understand homogeneous nucleation, and the creation of (p, T) phase diagrams. The methodology was shown to possess distinct advantages over the more commonly used combination of characterization techniques. 

Nowadays, for a thermodynainicist, /pVT-calorimetry (further referred to as scanning transitiometry, its patented and commercial name ) is the most accomplished experimental concept. It allows direct determinations of the most important thermodynamic derivatives it shows how, in practice, the Maxwell relations can be used to fully satisfy the thermodynamic consistency of those derivatives. Of particular interest is the use of pressure as an independent variable this is typically illustrated by the relatively newly established pressure-controlled scanning calorimeters (PCSC). - Basically, the isobaric expansibility Op(p,T) =il/v)(dv/dT)p can be considered as the key quantity from which the molar volume, v, can be obtained and therefore all subsequent molar thermodynamic derivatives with respect to pressure. Knowing the molar volume as a function of p at the reference temperature, Tg, the determination of the foregoing pressure derivatives only requires the measurement of the isobaric expansibilities as... 

Figure 4 Thermomechanical coefficients a, Kp and Py of n-hexane at 507.2 K determined by volume-controlled scanning transitiometry...

Scanning transitiometry is an extremely useful technique for studying phase transitions. Different transitions, mainly in polymer systems under various constraints of pressure, temperature, or chemical reagents, are reported hereafter. 

Figure 8 Illustration of the scanning transitiometry technique for low-temperature, high-pressure investigation of polymers glass transition. The pressure coefficient of the glass transition temperature is given in the inset...

Fig. 4 Scanning transitiometry setup for in situ simultaneous determination of the thermal and mechanical derivatives. For convenience, two types of cells are shown on the is the standard high pressure cell and on the right is a reaction-type cell that can accommodate various accessories (stirrer, reagents feeding, capillaries, optical hhos ot probes for UV/Vis/near-IR spectroscopic analysis)...

Scanning transitiometry has been used to determine the gas-polymer interaction energy, for instance upon CO2 sorption in MDPE and in PVDF samples (Fig. 9). 

Scanning transitiometry has been used to evaluate the pressure dependence of the isotropic transition temperature T , as well as the transition enthalpy and... 

Abstract Gas polymer interactions play a pivotal role in the formation of different molecular organizations/reorganizations of polymeric structures. Such structural modifications can have a negative impact on the material properties and should be understood in order to prevent them or these modifications are of engineering interest and they should be purposely tailored and properly controlled. Two newly developed techniques, gas-sorption/solubility and scanning transitiometry, are shown to be well adapted to provide the necessary (key) data to better understand and monitor the polymeric modifications observed under the triple constraints of temperature, elevated pressure, and gas sorption. This article illustrates the major contribution of gas polymer interactions in different intercoimected applied and engineering fields of the petroleum industry, polymer science, and microelectronics. 

Practically, the technique utilizes the principle of differential heat flux calorimetry, with which it is possible to operate under four thermodynamic situations where the perfectly controlled variation (or perturbation) of one of the three state variables (p, V, or T) is simultaneously recorded with the thermal effect resulting from the generated perturbation of the system under investigation. The principle of scanning transitiometry [23] offers the possibility to scan, in the measuring calorimetric cell, one of the three independent thermodynamic variables (p, V, or T)... 

Fig. 3 Thermodynamic scheme of scanning transitiometry showing the four possible modes of scanning. Each of these modes delivers two output derivatives (mechanical and thermal), which in turn lead to four pairs of the different thermomechanical coefficients, namely Op, Kj, /8v. Cp, and Cv...

Fig. 10 Three differential modes of scanning transitiometry according to the differential principle of the calorimetric detector, taking into account the respective roles of the measuring (M) and reference (R) vessels and the content of the reference vessel, (a) Thermal I differential without reference sample mode, (b) Thermal II differential with reference sample mode, (c) Thermal II differential comparative mode in this case a direct comparison between two polymers (MDPE and PVDF) samples is possible...

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