Electrical properties dielectric spectroscopy

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 or culture capacitance measurement is used as an on-line, non-invasive method for biomass estimation (see the chapter by Sonnleitner in this issue - the section on electrical properties) and responds mainly to living cells [43,44]. Observed difficulties in using the signal as a pure biomass concentration sensor, i.e. deviations from the simple correlation with cell density, were attributed to dependencies on the physiological state [43], and could be used to discriminate different populations in yeast cultures [45]. Connections with morphological features could be found for budding yeast... 

Concerning the two-layer model, the thickness and properties of each layer depend on the nature of the electrolyte and the anodisation conditions. For the application, a permanent control of thickness and electrical properties is necessary. In the present chapter, electrochemical impedance spectroscopy (EIS) was used to study the film properties. The EIS measurements can provide accurate information on the dielectric properties and the thickness of the barrier layer [13-14]. The porous layer cannot be studied by impedance measurements because of the high conductivity of the electrolyte in the pores [15]. The total thickness of the aluminium oxide films was determined by scanning electron microscopy. The thickness of the single layers was then calculated. The information on the film properties was confirmed by electrical characterisation performed on metal/insulator/metal (MIM) structures. 

The rates of change (slopes of the curves) of many important properties (such as the refractive index, surface tension, and gas permeabilities) as a function of temperature, the value of the dielectric constant, and many other optical and electrical properties, often change considerably at Tg. These changes enable the measurement of Tg by using techniques such as refractometry and dielectric relaxation spectroscopy. Refractometry provides results which are similar to those obtained from dilatometry, because of the correlation between the rates of change of the specific volume and of the refractive index with temperature. Dielectric relaxation spectroscopy is based on general physical principles which are similar to those in dynamic mechanical spectroscopy, the main difference being in its use of an electrical rather than a mechanical stimulus. 

This paper is primarily concerned with the techniques usually described as time domain spectroscopy (TDS) or time domain reflectom-etry (TDR). These have been most commonly applied to studies of time or frequency dependent behavior of dielectrics with negligible ohmic or d.c. conductance, but can be used for substances with appreciable conductance and indeed for studies of any electrical properties which can be characterized by an effective admittance or impedance. 

In this paragraph, electric oscillations are our concern. The experimental tool is impedance spectroscopy. It provides infoimation on electric properties and electrochemical processes proceeding in materials. We are focusing in the following on electric properties of polymer electrolytes that form dielectrics. 

M. E. Baird, Electrical Properties of Polymeric Materials, Plastics Institute, London, 1973. P. Hedvig, Dielectric Spectroscopy of Polymers, Halsted, New York, 1975. 

Structural properties can be investigated by small-angle neutron scattering (SANS) [3-5] or by quasi-elastic light scattering (QELS) [6-8]. Interphasal properties can be studied by dielectric spectroscopy and electrical conductivity mea-... 

Kochetov R, Andritsch T, Morshuis PHF, Smit JJ (2012) Anomalous behaviour of the dielectric spectroscopy response of nanocomposites. IEEE Trans Diel Electr Insnl 19 107-117 Kojima Y, Usuki A, Kawasumi M, Okada A, Fukushima Y, Kurauchi T, Kamigaito O (1993) Mechanical properties of nylon 6-clay hybrid. J Mater Res 8 1185-1189 Kolesov SN (1980) The influence of morphology on the electric strength of polymer insulation. IEEE Trans Electr Insul 15 382-388... 

Besides spectroscopy methods, other techniques have also been proposed for the in-line monitoring of the water content in single vials among them, dielectric measurements (Suherman et al, 2002) seem the most promising, at least for detection of the endpoint the electrodes can be placed outside the vial to reduce interference with the process. Monitoring of electric properties, and in particular of the product resistance (or inductance), has also been proposed. The technique seems suitable especially for substances that show a sharp eutectic melting, as in this case... 

Impedance spectroscopy (IS) is a versatile and powerfiil characteization technique for the investigation of frequency dependent electrical properties of materials and interfaces. It can be used to investigate the dynamics of boimd or mobile charge, both in the bulk and in interfacial regions of any kind of soUd or Uquid material with electronic, ionic, semiconducting, mixed electronic-ionic conductivity or even dielectric properties (Macdonald, 1987a). 

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