Time-domain dielectric spectroscopy

This chapter concentrates on the results of DS study of the structure, dynamics, and macroscopic behavior of complex materials. First, we present an introduction to the basic concepts of dielectric polarization in static and time-dependent fields, before the dielectric spectroscopy technique itself is reviewed for both frequency and time domains. This part has three sections, namely, broadband dielectric spectroscopy, time-domain dielectric spectroscopy, and a section where different aspects of data treatment and fitting routines are discussed in detail. Then, some examples of dielectric responses observed in various disordered materials are presented. Finally, we will consider the experimental evidence of non-Debye dielectric responses in several complex disordered systems such as microemulsions, porous glasses, porous silicon, H-bonding liquids, aqueous solutions of polymers, and composite materials. 

Time Domain Dielectric Spectroscopy Time Domain Reflectometry... 

The observation of slow, confined water motion in AOT reverse micelles is also supported by measured dielectric relaxation of the water pool. Using terahertz time-domain spectroscopy, the dielectric properties of water in the reverse micelles have been investigated by Mittleman et al. [36]. They found that both the time scale and amplitude of the relaxation was smaller than those of bulk water. They attributed these results to the reduction of long-range collective motion due to the confinement of the water in the nanometer-sized micelles. These results suggested that free water motion in the reverse micelles are not equivalent to bulk solvation dynamics. 

The successful development of the time-domain dielectric spectroscopy method (generally called time-domain spectroscopy, TDS) [79-86] and broadband dielectric spectroscopy (BDS) [3,87-90] have radically changed the attitude towards DS, making it an effective tool for investigation of solids and liquids on the macroscopic, mesoscopic, and, to some extent, microscopic levels. 

In order to actually cover 19 decades in frequency, dielectric spectroscopy makes use of different measurement techniques each working at its optimum in a particular frequency range. The techniques most commonly applied include time-domain spectroscopy, frequency response analysis, coaxial reflection and transmission methods, and at the highest frequencies quasi-optical and Fourier transform infrared spectroscopy (cf. Fig. 2). A detailed review of these techniques can be found in Kremer and Schonhals [37] and in Lunkenheimer [45], so that in the present context only a few aspects will be summarized. 

Time Domain Spectroscopy (T.D.S.).—Transient dielectric methods for the study of molecular motions occurring in less than 10 s are a relatively recent addition to the chemist s armoury. The availability of tunnd diode pulse-geam ators and wide-band sampling oscilloscopes led to the devdop-ment in the 1960 s of pulse reflection techniques known as time domain reilectometry (Ld.r.). The value of these methods was soon recognized in the fields of electronic and communication engineering for the qualitative analysis of transmission line systems and by 1965 had been used for... 

Time Domain Spectroscopy Basic Theory Experimental Methods Application to Dielectric Measurements Polar Liquids... 

Jiang Z, Li M, Zhang X-C (2000) Dielectric constant measuement for thin Aims differential time-domain spectroscopy. Appl Phys Lett 76 3221-3223... 

Fordedal H, Midttun O, Sjoblom J, Kvalheim OM, Schildberg Y, Voile JL. A multivariate screening analysis of W/O emulsions in high external electric fields as studied by means of dielectric time domain spectroscopy. II. Model emulsions stabilized by interfacially active fractions from crude oils. J. Colloid Interface Sci 1996 182 117-125. 

T. Sun, S. Gawad, N. G. Green and H. Morgan, Dielectric spectroscopy of single cells time domain analysis using Maxwell s mixture equation, J. Phys. D. Appl Phys., 40, 1-8 (2007). 

These authors noted that the intermediate power law (i.e., t l+y, with a small positive 7) of the OKE data was formally equivalent to the excess wing in the frequency-dependent susceptibility, the latter discussed in the dielectric literature since 1951. Brodin and Rossler argued that the intermediate power law observed in the OKE data was in essence a manifestation of the excess wing of the corresponding frequency-domain data, known long since from broadband dielectric spectroscopy and anticipated from DLS studies of supercooled liquids [83]. More recently, these authors showed that the excess wing was an equally common feature of the DLS data and discussed the merits of the Mode coupling theory analysis of the time and frequency-domain data [84]. 

Dielectric relaxation spectroscopy can probe the very broad time domain between 10 and 10 s. In principle, therefore, this method can be used... 

In this section we have demonstrated the potential of time-domain dielectric spectroscopy in obtaining information about both the structiue and dynamics of ionic and nonionic microemulsions on different temporal scales. 

Figure 2 Aqueous droplets dispersed in crade oil and sub-jected to an electric field (a) no field (b) 5 s, 1 kV/cm -droplet orientation in chains along the direction of the field. The droplets become small net dipoles in the dielectric oil continuum and are attracted to each other, forming chains in the direction of the field. High field strengths will cause interdroplet membrane rupture and coalescence. The principle has been utilized for measuring emulsion stability (i.e., resistance to electrically forced breakdown) in the high voltage-time domain spectroscopy (HiV-TDS) (71,72) and conductivity techniques (73).

One of the methods used to study emulsions has been the use of dielectric spectroscopy. The permittivity of the emulsion can be used to characterize an emulsion and assign a stability (1,42,48—54). The Sjoblom group has measured the dielectric spectra using time-domain spectroscopy (TDS) technique. A sample is placed at the end of a coaxial line to measure total reflection. Reflected pulses are observed in time windows of 20 ns, Fourier transformed in the frequency range from 50 MHz to 2 GHz, and the complex permittivity calculated. Water or air can be used as reference sample. The total complex permittivity at a frequency (co) is given by ... 

T Jakobsen. Cblathrate Hydrates Studied by Means of Time-domain Dielectric Spectroscopy. Thesis, University of Bergen, Norway, 1996. 

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. 

Feldman, Y., Ermolina, I., Hayashi, Y., 2003. Time domain dielectric spectroscopy study of biological systems. IEEE Trans. Dielectr. Elecfr. Insul. 10, 728—753. 

Polevaya Y, Ermolina I, Schlesinger M, Ginzburg BZ, Feldman Y (1999) Time domain dielectric spectroscopy study of human cells II. Normal and malignant white blood cells. Biochim Biophys Acta 1419 257-271... 

---