Thermally stimulated current spectroscopy relaxations

Thermally stimulated current (TSC) spectroscopy is used to characterize the relaxation processes and structural transitions occurring in samples that have been polarized at a temperature greater than the temperature where molecular motion in the sample is enhanced and subsequently quenched so that the high mobility state is frozen. On heating the sample at a controlled rate, depolarization of the polymer electrets (molecular or ionic dipoles, trapped electrons, mobile ions) occurs and the oriented dipoles, frozen in the quenched sample, relax to a state of thermal equilibrium. This relaxation process is observed as a depolarization current, which is typically of the order of picoamperes, and is referred to as the thermally stimulated current. 

BordaUo HN, Zakharov BA, Boldyreva EV, Johnson MR, Koza MM, Seydel T, Fischer J (2012) Application of incoherent inelastic neutron scattering in pharmaceutical analysis relaxation dynamics in phenacetin. Mol Pharm 9 2434-2441 Bptker JP, Karmwar P, Strachan CJ, Cornett C, Tian F, Zujovic Z, Rantanen J, Rades T (2011) Assessment of crystalline disorder in cryo-milled samples of indomethacin using atomic pairwise distribution functions. Int J Pharm 417 112-119 Boutonnet-Fagegaltier N, Menegotto J, Lamure A, Duplaa H, Caron A, Lacabanne C, Bauer M (2002) Molecular mobihty study of amorphous and crystalline phases of a pharmaceutical product by thermally stimulated current spectrometry. J Pharm Sci 91 1548-1560 Bras AR, Noronha JP, Antunes AMM, Cardoso MM, Schdnhals A, Affouard Fdr, Dionfsio M, Correia NIT (2008) Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy. J Phys Chem B 112 11087-11099... 

Abbreviations DEA, dielectric analysis >OC. degree of crystallinity DSC, di erential scanning calorimetry LM, local mobility (secondary relaxations) SR, structural relaxation 7g, determination of glass transition temperature TSDC. thermally stimulated depolarization current spectroscopy XRD, X-ray difTractometry. Source Adapted from Ref. 15. 

In Chapter 7, Mano and Dionisio describe how electrical methods, and particularly dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarisation current (TSDS) techniques, play a major role as tools for e2q)loring molecular mobility. DRS enables molecular relaxational processes (both slow and fast) to be studied. For example, the localized motions of glass formers in the glassy state give rise to local fluctuations of the dipole vector that are the origin of the secondary relaxation processes detected by dielectric relaxation spectroscopy, while above, but near, the glass transition, cooperative motions result in a distinguishably different relaxation process (the a-relaxation). 

Saxena Pooja, Gaur Mulayam Singh, Shukla Prashant, et al. Relaxation investigations in polysulfone Thermally stimulated discharge current and dielectric spectroscopy. J. Electrostat. 66 no. 11-12 (2008) 584-588. 

Dielectric Relaxation Spectroscopy and Thermally Stimulated Depolarization Current... 

The molecular mobility and microphase separation in blends of crosslinked polyurethane (PUR) and styrene-acrylonitrile (SAN) copolymer were investigated. The PUR and SAN copolymer were prepared by reactive blending with polymer polyols. DSC, thermally stimulated depolarisation currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS) and dynamic mechanical thermal analysis over a wide range of... 

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