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Publié par | universitat_augsburg |
Publié le | 01 janvier 2010 |
Nombre de lectures | 14 |
Poids de l'ouvrage | 2 Mo |
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RELAXATION, RATTLING AND DECOUPLING
Dynamic Processes in Glassy Matter
Dissertation zur Erlangung des Doktorgrades
(Dr. rer. nat.)
der Mathematisch‐Naturwissenschaftlichen Fakultät
der Universität Augsburg
vorgelegt von
Melanie Köhler
Institut für Physik
Elektronische Korrelationen und Magnetismus
Lehrstuhl für Experimentalphysik V
Augsburg, Mai 2010
1. Gutachter: Prof. Dr. A. Loidl
2. Prof. Dr. A. Reller
Tag der Einreichung: 21. Mai 2010
Tag der mündlichen Prüfung: 15. Juli 2010
Wer so tut, als bringe er die Menschen zum Nachdenken, den lieben sie.
Wer sie wirklich zum Nachdenken bringt, den hassen sie.
Aldous Huxley
1 Introduction ................................................................................................. 1
2 Phenomenological and theoretical predictions .................................................. 5
2.1 Principles of dielectric spectroscopy ..................................................................... 6
2.1.1 Relaxation in matter ____________________________________________________ 6
2.2 Dielectric response of glass‐forming liquids .......................................................... 8
2.2.1 The ‐relaxation _______________________________________________________________ 9
2.2.2 Excess wing and slow ‐process _________________________________________________ 11
2.2.3 The fast ‐process ____________________________________________________________ 11
2.2.4 The boson peak 12
2.3 Hallmark features of glass‐forming liquids 14
2.3.1 Non‐Arrhenius behaviour _______________________________________________________ 15
2.3.2 Non‐exponential relaxation functions _____________________________________________ 16
2.3.3 Non‐ergodicity 17
2.4 Models and theories ......................................................................................... 18
2.4.1 Explanations of the Johari‐Goldstein (JG) ‐relaxation _______________________________ 18
2.4.2 Minimal model _______________________________________________________________ 20
2.4.3 Coupling model 22
2.4.4 Extended coupling model_______________________________________________________ 23
2.4.5 Mode coupling theory (MCT) ____________________________________________________ 24
2.4.6 Ionic conductivity: phenomenological approaches and models ________________________ 30
3 Measurement techniques .............................................................................. 33
3.1 Dielectric measurements .................................................................................. 34
3.1.1 Low frequency techniques ______________________________________________________ 36
3.1.2 Coaxial line techniques _________________________________________________________ 38
3.1.3 Quasioptical method: submillimeter wave spectroscopy _____________________________ 40
3.1.4 Fourier transform infrared spectroscopy (FTIR) _____________________________________ 43
3.2 Neutron scattering ........................................................................................... 44
3.2.1 The high‐resolution time‐of‐flight spectrometer TOFTOF ____________________________ 45
3.3 Positron annihilation lifetime spectroscopy (PALS) ............................................. 46
3.4 Overview on the methods: advantages and disadvantages .................................. 47
4 Results and discussion ................................................................................. 49
4.1 Broadband dielectric spectra of glass‐forming liquids .......................................... 50
4.1.1 Salol and xylitol – discussion of a "Type A" and "Type B" system _______________________ 50
4.1.2 The structural glass‐former benzophenone ________________________________________ 56
4.2 Glassy dynamics in mono‐, di‐, and tripropylene glycol ........................................ 60
4.2.1 Broadband dielectric spectra ____________________________________________________ 60
4.2.2 The ‐relaxation ______________________________________________________________ 63
4.2.3 Secondary relaxations _________________________________________________________ 65
4.2.4 The fast ‐relaxation __________________________________________________________ 68
4.2.5 The boson peak _______________________________________________________________ 77
4.2.6 Relaxational behaviour of the polymer PPG 4000 ___________________________________ 79
i 4.2.7 Comparison with other experimental methods _____________________________________ 82
4.3 Influence of the ion content on slow and fast relaxation dynamics ........................ 92
4.3.1 The ‐relaxation ______________________________________________________________ 92
4.3.2 Slow ‐process and excess wing ________________________________________________ 103
4.3.3 High frequency response ______________________________________________________ 105
4.3.4 Neutron scattering vs. dielectric spectroscopy 114
4.4 Relationship between fragility and the boson peak ............................................ 119
5 Summary and conclusion ............................................................................. 125
6 Appendices ............................................................................................... 129
6.1 S‐parameter ................................................................................................... 130
6.2 From the correlation function to the structure factor ......................................... 131
6.3 Behaviour of the correlation function , š; ..................................................... 133
7 Bibliography .............................................................................................. 135
ii
List of abbreviations:
BP boson peak
BWO backward wave oscillator
BZP benzophenone
CC Cole‐Cole
CD Cole‐Davidson
CM coupling model
(D)LS (dynamic) light scattering
DOS density of states
DPG dipropylene glycol
EW excess wing
FIR far infrared
FTIR Fourier transform infrared
HN Havriliak‐Negami
JG Johari‐Goldstein
KWW K