Thermally stimulated depolarization currents TSDC

A detailed discussion of the statistical thermodynamic aspects of thermally stimulated dielectric relaxation is not provided here. It should suffice to state that kinetics of most of the processes are again complicated and that the phenomenological kinetic theories used to described thermally stimulated currents make use of assumptions that, being necessary to simplify the formalism, may not always be justified. Just as in the general case, TSL and TSC, the spectroscopic information may in principle be available from the measurement of thermally stimulated depolarization current (TSDC). However, it is frequently impossible to extract it unambiguously from such experiments. 

Figure 21. Schematic diagram of an apparatus for thermally stimulated depolarization current (TSDC) experiments.

TSC is a technique for detecting the transitions that depend on changes in the mobility of molecular scale dipolar structural units. TSC is based on the ability of polar molecules to be moved by an electrostatic field. Two types of current are generated thermally stimulated polarization current (TSPC) and thermally stimulated depolarization current (TSDC). TSPC is generated when dipolar structures orient in a static electric field with increasing in the temperature. TSDC is generated because of the relaxation of the previously polarized molecules as reported in Fig. 5. 

Another TL application is the analysis of the electronics states in materials, which are defined by both material and technology of its production. For example, for PS different contact methods to define the electronics states in metal/PS stmctures have been aheady applied thermally stimulated depolarization currents (TSDC) and thermally stimulated current (TSC) (Ciurea et al. 1998 Anastasiadis and Triantis 2000 Brodovoy et al. 2002), optical charging spectroscopy (OCS) (Ciurea et al. 2000), and deep-level transient spectroscopy (DLTS) (Pincik et al. 1999 Tretyak et al. 2003). The mentioned methods determine the parameters of traps related with both PS material and metal/PS interface and often differ from results obtained from TL experiments. Two advantages of the TL method are that it is contactless and it can reveal the energy distribution of both bulk and/or surface states. The obvious drawback of TL is that it can only be applied to luminescent materials. 

Jain D, Chandra LSS, Nath R, Ganesan V (2012) Low temperature thermal windowing (TW) thermally stimulated depolarization current (TSDC) setup. Meas Sci Technol 23 025603 Janssens S, Van den Mooter G (2009) Review physical chemistry of solid dispersions. J Pharm... 

Hongo T., Koizumi T., Yamane C., and Okajima K. 1996. Thermally stimulated depolarized current (TSDC) analysis on the structural change of regenerated cellulose membranes caused by the change in water content. Polym J 28 1077 1083. 

In series of publications [25,27,29,35-40] several methods were used for eharaeterization of the microphase structure of the semi-IPNs studied. Small-angle X-ray seattering (SAXS), differential scanning calorimetry (DSC) [27, 35-37], dynamic mechanical thermal analysis (DMTA) [27, 30-32], dielectric relaxation spectroseopy (DRS), and thermally stimulated depolarization currents (TSDC) [25, 39, 40] measurements have shown that pure PCN is characterized by a typical homogeneous structure, but for segmented LPU the microphase separation on the level of hard and soft domains due to their thermodynamic immiscibUity was denoted. As for semi-IPNs, the destruction of the microphase separated morphology of LPU was observed and the microphase separation between PCN and LPU phases, expected from the difference of solubility parameters, was not found. 

Some secondary relaxations of the components in thermoplastic AIPNs have been investigated by thermally stimulated depolarization current (TSDC) techniques and thermally stimulated conductivity (TSC) measurements [10,11]. It was found that upon addition of S-co-AA to CPU, the secondary and 3 CPU peaks (at ca. -140 °C and ca. -100 °C, respectively) shift slightly to lower temperatures, i.e., the corresponding relaxations become faster, these shifts being more pronounced at low S-co-AA contents. The shifts can be related to physical interactions between the IPN components and to their partial miscibility. Rizos et al. [15] have shown that as a result of such interactions, changes in the local free volume may occur, affecting the secondary relaxation times. The same changes in the [3 relaxation of PU have been found in polyurethane/polystyrene IPNs by Pandit and Nadkarni [16]. 

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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