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Abstract  

Scanning transitiometry combines three state variables (P,V,T) with a heat effect measured in strictly defined thermodynamic conditions. By slowly scanning one of the state variables when the other one is kept constant, the transitiometer permits to determine simultaneously two thermodynamic derivatives, always one is thermal and the other one mechanical. This study presents a number of applications of scanning transitiometry in various fields (dense liquids, supercritical systems, polymers, food systems) and presents results, often impossible to obtain with other known techniques.

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Basic principle of scanning transitiometry are presented. The new technique is based on a simultaneous recording of both mechanical and thermal variables of a thermodynamic transition induced by scanning one independent variable (p, T orV) while the other independent variable is being kept constant. Examples are given for applications of the new technique in materials science such as simultaneous determination of αp and kt as a function of pressure for a crystalline polyethylene at 363 K, simultaneous determination of heat and volume of transition for isothermal fusion of polyethylene at 423 K and for isobaric phase changes in ¯110S5 liquid crystal (4-n-pentyl-phenyl-thiol-4′-decycloxybenzoate) at 134.6 MPa. A special attention is paid to the determination of αp for dense liquids, theoretical interpretation of its pressure-temperature behavior and the use of the new technique in verification of equations of state for dense condensed systems.

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Abstract  

The effects of nitrogen (N2) pressure on amphiphilic di-block copolymer, PEO114-b-PMA(Az)40, were investigated by scanning transitiometry. The isotropic transition temperature increased with the increase of pressure above 20 MPa. The hydrostatic pressure effects evaluated with the Clapeyron equation were smaller than the value obtained by mercury as a pressurizing medium because the amount of absorbed gas decreases the volume change at the isotropic transition.

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Abstract  

The effects of high pressure carbon dioxide (CO2) on the isotropic transition of three different amphiphilic di-block copolymers, PEOm-b-PMA(Az)n, namely PEO114-b-PMA(Az)40, PEO272-b-PMA(Az)46 and PEO454-b-PMA(Az)47, and on PMA(Az)30 homopolymer have been investigated by scanning transitiometry. Under CO2 pressure, the isotropic transition temperature decreased with the increase of pressure up to around 30 MPa due to CO2 sorption and increased above 40 MPa. Transition entropy of the isotropic transition indicated that the depression of the isotropic transition temperature was caused by the adsorption of CO2 into the azobenzene moieties and that the increase above 40 MPa was caused by the desorption of CO2 into the azobenzene moieties. Comparison between PEOm-b-PMA(Az)n copolymers and PMA(Az) homopolymer clarified PEO domain acted CO2 pathway to approach the equilibrium state rapidly.

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Abstract  

A scanning transitiometer has been used in investigations of 1st and 2nd order phase transformations in polymers. It was demonstrated taking as an example fusion of polyethylene at 200 MPa with a temperature scan as inducing variable that by recording simultaneously the rate of heat exchange and the rate of volume variations it is possible to determine in a single experiment the pressure derivative of temperature of this 1st order phase transition. For phase transformations similar to the 2nd order transitions the transitiometric analysis permits simultaneous measurements of pairs of thermodynamic derivatives which permit determination of pressure effects according to the Ehrenfest equations. For the glass transition in polystyrene at high pressures the pressure effect was similar independently of the pair of thermodynamic derivatives used (heat capacity and thermal expansivity or compressibility and thermal expansibility).

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Journal of Thermal Analysis and Calorimetry
Authors: S. Boyer, J-P. Grolier, L. Pison, C. Iwamoto, H. Yoshida, and T. Iyoda

Abstract  

The present work deals with the interactions between carbon dioxide, used as pressure medium, either in the gas state (GCO2) or in the supercritical state (SCCO2) and amphiphilic di-block copolymers PEOm-b-PMA(Az)n. The effect of pressure on the isotropic transition of the PEOm-b-PMA(Az)n copolymer was investigated using scanning transitiometry (ST). The experimental results were compared with those measured when using ‘relatively inert’ mercury (Hg) as pressure medium. Morphological observation of a PEOm-b-PMA(Az)n thin film submitted to SCCO2 was performed by atomic force microscopy (AFM) to investigate the nano-structure organization. These results indicate the possibility of modifying the nano-structure in a specific way depending on the CO2 physical state.

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