Real-time Dielectric Spectroscopy

On-line real-time microdielectrometry of epoxy/ fibreglass composite curing was reported [260]. DIES may be used for in-line curing or drying reactions, for the determination of water in polyamides, for (water) level indication (axiometrics) and for phase inversion detection in water/oil systems. 

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Ezquerra T A, Roslaniec Z, L6pez-Cabarcos E and Balt i-Calleja F J (1995) Phase separation and crystallization phenomena in a poly(ester-carbonate) block copol5Tner A real-time dielectric spectroscopy and X-ray scattering study, Macromolecules 28 4516-4524. 

The crosslinking kinetics of a thin polymeric layer on a prepolymer of a phthalic acid diallyl ester was studied by real-time dielectric spectroscopy. Activation energies were estimated for the reaction using the temperature dependence of the time constant. The change of the relaxation rate of the dynamic Tg with the reaction time was obtained from dielectric loss data. 20 refs. 

Macromolecular Chemistry Physics 202, No.16, 7th Nov. 2001, p.3228-33 CHARACTERIZATION OF THE CROSSLBVKING KINETICS OF A THIN POLYMERIC LAYER BY REAL-TIME DIELECTRIC RELAXATION SPECTROSCOPY Schonhals A Fritz A Pfeiffer K Berlin,University Micro Resist Technology GmbH... 

This laboratory long ago devised [120] the use of radio-frequency dielectric spectroscopy [121, 122] for the on-line and real-time estimation of microbial and other cellular biomass during laboratory and industrial fermentations. The principle of operation is that only intact cells (see [123] for what is meant in this context by the word viable ), and nothing else likely to be in a fermentor, have intact plasma membranes and that the measurement of the electrical properties of these membranes allows the direct estimation of cellular biomass (Fig. 4). 

Dielectric spectroscopy techniques are promising for numerous applications that require non-invasive, non-destructive, non-contact, and real-time measurements. Non-invasive measurements with gas, liquid, solid, and mixed samples are possible on distance scales from nanometers to meters and a frequency of excitation from microhertz to terahertz. The main advantages of fringing electric field dielectric sensors include one-side access to material under test, convenience of application... 

Andjelic, S. and Fitz, B. D., Study of reorientational dynamics during real-time crystallization of absorbable poly(p-dioxanone) by dielectric relaxation spectroscopy,. Polym. Sd. Polym. Phys. Ed., 38, 2436, 2000. 

Asami, K., Gheorghiu, E., Yonezawa, T., 1999. Real-time moDitoring of yeast cell division by dielectric spectroscopy. Biophys. J. 76, 3345—3348. 

For polymers, dielectric spectroscopy is sensitive to fluctuations of dipoles, which are related to the molecular mobility of groups, segments, or the polymer chain as well [38]. The molecular mobility is taken as a probe for structure. The basic quantity is the complex dielectric function e f) = t (f) - it"(f) as a function of the frequency/and the temperature T. s (/) is the real whereas e"(/) is the loss part i = >f ). A relaxation process is indicated by a step-like decrease of s (/) with increasing frequency and a peak in e"(/). From the maximum position of the peak a mean relaxation rate can be deduced, which corresponds to the relaxation time of the fluctuation of the dipole moment of a given structural imit. For details see reference [49]. All shown measurements were carried out isothermally in the frequency range from 10 to 10 Hz by an ALPHA analyzer (NovocontroF). The temperature of the sample is controlled by a Quatro Novocontrol system with stability better than 0.1 K. 

Although the investigation in this paper mainly concentrated on the time evolution of the 001 reflection and the 4-point pattern in the SAXS region, the measurements of the time dependence of overall diffraction patterns in the WAXS region will be required in order to elucidate the microscopic mechanism of the structure formation in oriented PET. In particular, real-time measurement of the intensity distribution of the meridional reflections of higher order will reveal the detailed mechanism of the structure formation. Real-time relaxation measurements such as dielectric relaxation spectroscopy are also desired for this purpose. 

Abstract. The simultaneous combination of scattering techniques, probing structure, with relaxation techniques, detecting modifications of the amorphous phase dynamics, can be helpful in order to obtain complementary information about crystallization processes in polar polymers. The objective of this contribution is to review the improvements in the combination of real time (wide and small angle) X-ray scattering and dielectric spectroscopy aiming at a better understanding of polymer crystallization. 

Examples of various correlation functions for the diblock copolymer system at high and at low temperatures are shown in Fig. 7. It has been observed that at high temperatures TjN = I), the systems behave like a homogeneous melt. All correlation functions show a single step relaxation. The fastest is the bond relaxation and the slowest is the chain relaxation described by the end-to-end vector autocorrelation function. The relaxation of the block is faster than the whole chain relaxation by a factor of approximately two. Such relations between various relaxation times in the disordered state of the copolymer can be regarded as confirmed experimentally for some real systems, in which the dielectric spectroscopy allows distinction of the different relaxation modes [41]. At low temperatures, drastic changes... 

Due to the generation of charge carriers, conjugated polymers become electrically conductive when irradiated with UV/visible light. The quantum yield for charge carrier generation is increased by additives, such as fullerene compounds. With the aid of time-resolved THz spectroscopy, the time- and frequency-dependent complex conductivity with its real and imaginary parts can be measured. THz radiation is absorbed by the polymer due to the dielectric... 

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