Calorimetric-dielectric measurements

Outline of Calorimetric-Dielectric Measurements of Absolute Masses of Adsorbates... 

Figure 1.23. Experimental setup for calorimetric-dielectric measurements of pure gas-adsorption-equiUbria (impedance calorimeter). IFT U Siegai, 2001, German Patent DE 10019122 A 1.

J.U. Keller, W. Zimmermann, A. Schein, R. Staudt Determination of absolute gas adsorption isotherms by eombined calorimetric and dielectric measurements. Adsorption (2002) in print. 

Determination of Absolute Gas Adsorption Isotherms by Combined Calorimetric and Dielectric Measurements, Adsorption, 9 (2003) p. 177-188. 

The glass transition temperature for polymer blends often shows broadening (broader relaxation spectra for dynamic mechanical and dielectric measurements and broader transitions for calorimetric measurements). These observation are generally observed for borderline misci-... 

In addition to X-ray and neutron-diffraction structural characterization, the physical properties of iron oxides have been studied by a wide variety of techniques. Most common are conventional transport, optical, dielectric, calorimetric and magnetic measurements. In addition, NMR and Mossbauer are widely used. 

Poly (diethyl siloxane) was suggested by Beatty et al. 1651 based on DSC, dielectric, NMR, and X-ray measurements to possess liquid crystalline type order between about 270 and 300 K. The macromolecule shows two large lower temperature first order transitions, one at about 200 K, the other at about 270 K166 ll,7). The transition of the possible mesophase to the isotropic liquid at 300 K is quite small and irre-producible, so that variable, partial crystallinity was proposed 165) [measured heat of transition about 150 J/mole1S8)], Very little can be said about this state which may even consist of residual crystals. It is of interest, however, to further analyze the high temperature crystal phase between 200 and 270 K. It is produced from the, most likely, fully ordered crystal with an estimated heat and entropy of transition of 5.62kJ/mol and 28J/(Kmol), respectively [calculated from calorimetric data 1S6)... 

The dielectric relaxation of bulk mixtures of poly(2jS-di-methylphenylene oxide) and atactic polystyrene has been measured as a function of sample composition, frequency, and temperature. The results are compared with earlier dynamic mechanical and (differential scanning) calorimetric studies of the same samples. It is concluded that the polymers are miscible but probably not at a segmental level. A detailed analysis suggests that the particular samples investigated may be considered in terms of a continuous phase-dispersed phase concept, in which the former is a PS-rich and the latter a PPO-rich material, except for the sample containing 75% PPO-25% PS in which the converse is postulated. 

A. Kyritsis, P. Pissis, J. L. Gomez Ribelles, and M. Monleon Pradas, Polymer-water interactions in poly(hydroxyethyl acrylate) hydrogels studied by dielectric, calorimetric and sorption isotherm measurements, Polym. Gels Networks 3, 445-469 (1995). 

Figure 11. T0 as a function PVC concentration as defined from initial rise in E", z, and Cp by dynamic mechanical (H), dielectric (O), and calorimetric (%) measurements, respectively...

Changes in physical state may be observed from changes in thermodynamic quantities, which can be measured by calorimetric techniques, dilatometry, and thermal analysis. Spectroscopic methods are also available for the determination of changes in molecular mobility around transition temperatures. In addition to the changes in thermodynamic quantities and molecular mobility, a glass transition has significant effects on mechanical and dielectric properties. 

There have been numerous studies employing calorimetric(19), dynamic mechanical, ( ) dielectric, ( ) and morphological(23,24) techniques to elucidate the solid-state behavior of styrene-ethylene oxide block copolymers. These measurements have focused on transition-temperature phenomena, and they have provided reference data on the bulk properties of the copolymers. The evidence accumulated to date indicates that PS and PEO are incompatible in the bulk. While this appears true, in general, one cannot rule out the possibility that PS and PEO have some limited degree of miscibility in the copolymers. It is also unknown, at this time, what influence an interface (e.g., the air-polymer interface) has... 

Fij . 11. Dielectric absorption of carboxyhemoglobin solutions o, experimental measurements of (A — k )/s ciuve A, k — k ) g, nnd curve B, J e"lg, calculated from equation i of Oncley Ferry and Shack, using the constants, recorded in Table 1 of their paper, for the calorimetric method. (J. Shack, Ph. D. dissertation Harvard University 1939-) From Oncley, Ferry and Shack (85). See also Oncley ( 3), page 444. 

Both the dielectric and the calorimetric results were found to be quite well reproducible in the whole concentration range studied but for two concentration values, C=0.270 and 0=0.353> where time dependent phenomena were observed upon ageing of the samples. Because of the latter effect, the two analyses were performed by taking the measurements respectively, 3-7-10-15-20 and 30 days after the preparation of each concentration tested. The latter study had the aim to follow the spontaneous evolution of the system until time independent both dielectric and calorimetric behaviors were obtained. The dielectric study of the time dependent phenomena was carried out at the fixed frequency of 10 KHz. 

The assignment of the alpha relaxation was additionally confirmed by AC-calorimetric measurements on thin films of POHOAc [31], The effect of confinement on the overall dynamics of POHOAc is given in Fig. 24, showing the dielectric spectra for different film thicknesses, ranging from 310 nm down to 17 nm. While the beta and the gamma relaxations, as local processes, are not affected with decreasing film thickness (except a decrease of the dielectric... 

Whatever the scenario followed, it is accepted that two distinct processes occur above and below the crossover as shown clearly, e.g. for PHMA by dielectric, shear and calorimetric measurements that established that the cooperativity onset took place in the crossover region [49]. 

In the last decade Mishchenko and co-workers have made extensive calorimetric measurements, primarily in solvents of low dielectric constant, and many of these data have been compiled by Mishchenko and Poltoratskii. Several of the papers deal with methanol or methanol-water solutions. For the most part their investigations cover wide concentration ranges, from... 

Physical properties of the first-shell water of macromolecular water shell differ from the bulk water properties. Some of them can be measured experimentally. They are the phase transition temperature, dielectric constant, NMR relaxation parameters, calorimetric characteristics, kinetic characteristics, such as self-diffusion coefficient and some others. The rrrain factors that define protein structure are residue sequence, hydration, iorric arrd hydrophobic irrleractions. 

For studies of polymers cmifined inside nanoporous host systems, the most comprehensive study was reported for polyfdimethyl siloxane) and polyfmethylphenyl siloxane) down to 5 nm by neutron scattering and dielectric and calorimetric measurements [165], An increase of molecular mobility, implying a decrease of Tg, was observed on decreasing the pore size. The increment of the specific heat capacity at the glass transition normalized by the mass of cmifined polymers also decreases with pore size, indicating a concomitant decrease of the cooperative length scale with a decrease of Tg. An explanation has been offered [163]. 

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