Thermally stimulated current spectroscopy measurements

The measurement and control of electrostatic charge has been studied more extensively on textile materials than on hair fibers. Methods reported in the literature for static charge measurements include resistivity measurements, Faraday cage [197], dielectric losses, and TSC (thermally stimulated current) spectroscopy [198],... 

Note that thermally stimulated current spectroscopy cannot be applied to conductive materials with a resistance smaller than lO Q/m thickness. In addition, the presence of space charges in the sample can produce artefacts. For solid samples the upper temperature limit of measurement is the onset of flow, which presents itself as a large current discharge. This discharge is due to the sample behaving like a battery and draining the charges accumulated at the surfaces. 

The presence of cooperative motion of chain segments present in intercalated polymer chains can be examined using various analytical techniques such as Differential Scanning Calorimetry (DSC), thermally stimulated current (TSC) and dielectric spectroscopy. DSC measurements on an intercalated PEO, (Mw= 100,000)/montmorillonite hybrid (20 wt. % polymer), indicated the absence of... 

Table 14.3 Structural properties of ASD measurable by thermally stimulated current (TSC) spectroscopy and possible hurdles...

Figure 6.12. Schematic of the apparatus used for thermally stimulated current (TSC) studies. The basic concept apphes also for slow time-domain spectroscopy measurements.

The previous section reviewed the advances of what may be termed the classical technique of dielectric spectroscopy, which has, as its modes of operation, measurements either at constant temperature or at constant frequency. Recently a technique which does not operate with these restrictions has been developed, particularly by van Tumhout This technique is variously termed thermally stimulated discharge (TSD) or thermally stimulated current (TSC). In its simplest form a material in the form of a disc with electrodes in intimate contact on opposite faces is heated to some forming temperature Tf. At this stage the sample is polarized by applying a strcsng electrostatic field ( 30 kV/cm) for an extended period. All polarization processes which are active at, or below the tenqjerature Tf and within the time the fidd has been on, will contribute to an overall polarization the material within the field is polarized. If the field were now removed at the temperature Tf, the polarization could be disdiarged as in the step response technique of the previous section. However, in TSD the temperature is reduced to some value < Tf with the field still on. Any polarization process which is non-active at but active between and Tf has thereby been frozen-in at T < Tg, even when the field is removed as in the TSD tech-... 

The organization of the present chapter is as follows. Dielectric techniques for molecular dynamics studies, in particular broadband dielectric spectroscopy (DS) and thermally stimulated depolarization currents (TSDC) techniques are shortly presented in the next section. Section 3, devoted to ionic conductivity measurements and analysis, focuses mostly on analysis, as the measuring techniques and equipment are often similar to those used for DS. The microphase separation and morphology of segmented PUs is discussed in the following Section 4, which completes the first introductory part of the chapter. Results obtained with selected PTE are presented in Section 5, followed by a larger Section 6 devoted to PU ionomers with ionic moieties in either of the HS and SS. PU ionomers of the latter type are often based on poly(ethylene oxide) (PEO) as the SS component and, for this reason. Section 6 includes a discussion of telechelics based on PEO, which may serve as model systems for PU ionomers. In Section 7, we discuss recent results obtained with nanocomposites based on PTE, a topic attracting much current interest, before we conclude with Section 8. 

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