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174 Summarizing discussion constant when evaluated at T g . In addition we find that the ratio expressed by R tentatively correlates with fragility. The correlation is of similar quality when comparing R with the isochoric fragility or with the isobaric fragility. Based on the pressure independence of R (which we find in the two systems where it has been studied) we speculate that the correlation to the intrinsic isochoric fragility is the more fundamental. A direct comparison of the spectra from different systems at varying temperatures, suggests that R evaluated at T g is more governed by the amount of quasi-elastic scattering than by the boson peak intensity. This indicates that more fragile systems might have more quasi-elastic scattering even at T g , where the alpha relaxation most certainly does not enter the experimental window.
Chapter 10 Perspectives In this work we have mainly used pressure experiments to test the robustness of empirically established “universalities”. In addition we have tested the robustness of the elastic models for the viscous slowing down and discussed several different proposed models for the boson peak. These models are formulated as explanations of phenomenology observed at atmospheric pressure. High pressure experiments therefore gives a valuable possibility of testing their predictive power. This type of test is relevant for almost any type of model or theory claiming to explain a general phenomenon in glass-formers. Particularly for explaining the viscous slowing down, it is clear that the relevant governing parameter should be constant along isochrones in the system. This implies for example that the Adam-Gibbs model predicts 1/(TS c (ρ, T))=constant and the shoving model predicts G ∞ (ρ, T)/T=constant along an isochrone. Especially the latter of these prediction could easily be tested in practice. Turning now to the phenomenology of glass-forming systems, we have established some trends that appear to be general. The system becomes harder when increasing pressure along the T g -isochrone, and the characteristic energy (or energies) of the system increases. The activation energy is for example higher (but E a /T is of course constant). The boson peak energy is higher at higher pressure and the mean square displacement has a lower amplitude. However, there are also a striking number of properties which are unaffected by pressure changes along the isochrone. (i) We find that the relative intensity of the boson peak is unaffected. (ii) The shape of the boson peak is not affected. (iii) The isochoric fragility is not affected. (iv) The shape of the alpha relaxation is not affected. (v) The mean square displacement normalised to the average molecular distance is not affected. Thus all these dynamical properties are intrinsic to a given system in the sense that they are unaffected by pressure - at least within a limited pressure range. From this we conclude that the mechanisms which govern the structural slowing down should have the same type of intrinsic character. 175
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THÈSE présentée par Kristine NIS
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Acknowledgement First of all I woul
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Contents Abstract iii Acknowledgeme
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CONTENTS ix 9 Summarizing discussio
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2 Introduction fragility with other
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Résumé du chapitre 2 De manière
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8 Slow and fast dynamics glass. The
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10 Slow and fast dynamics energy in
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12 Slow and fast dynamics increasin
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14 Slow and fast dynamics (linear)
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16 Slow and fast dynamics The dynam
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18 Slow and fast dynamics T > T 2
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20 Slow and fast dynamics as theore
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22 Slow and fast dynamics and sugge
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24 Slow and fast dynamics The boson
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26 Slow and fast dynamics modulus 3
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Chapter 3 What we learn from pressu
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3.2. Empirical scaling law and some
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3.3. Correlations with fragility 37
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3.4. Temperature dependences 39 mea
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3.5. Summary 41 assumption that the
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Chapter 4 Experimental techniques a
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4.2. Dielectric spectroscopy 47 4.1
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4.2. Dielectric spectroscopy 49 fie
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4.3. Inelastic Scattering Experimen
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Résumé du chapitre 5 La relaxatio
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72 Alpha Relaxation the dielectric
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74 Alpha Relaxation Measuring the c
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76 Alpha Relaxation 4 2 0 This work
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78 Alpha Relaxation for the 1 s iso
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80 Alpha Relaxation log10(τ α ) 2
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82 Alpha Relaxation 2 1 0 216.4K th
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84 Alpha Relaxation function has a
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86 Alpha Relaxation 2.5 2.5 2 2 log
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88 Alpha Relaxation 0.4 log 10 Im(
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90 Alpha Relaxation keeping the rel
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92 Alpha Relaxation correlation bet
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Chapter 6 High Q collective modes I
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6.1. Inelastic X-ray scattering 97
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6.2. Sound speed and attenuation 99
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6.3. Nonergodicity factor 105 where
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6.3. Nonergodicity factor 107 1 0.9
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6.3. Nonergodicity factor 109 high
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6.4. Nonergodicity factor and fragi
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6.5. Summary 117 d log (e(ρ))/ d l
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Résumé du chapitre 7 Dans ce chap
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122 Mean squared displacement colle
Page 134 and 135: 124 Mean squared displacement 1.5 I
Page 136 and 137: 126 Mean squared displacement 1.4 1
Page 138 and 139: 128 Mean squared displacement a cen
Page 140 and 141: 130 Mean squared displacement cumen
Page 142 and 143: 132 Mean squared displacement / a
Page 144 and 145: 134 Mean squared displacement I P i
Page 146 and 147: 136 Mean squared displacement as be
Page 149: Résumé du chapitre 8 Le pic de bo
Page 152 and 153: 142 Boson Peak The FEC-model sugges
Page 154 and 155: 144 Boson Peak the Qout Q in factor
Page 156 and 157: 146 Boson Peak We are mainly intere
Page 158 and 159: 148 Boson Peak 1.5 x 10−3 ω [meV
Page 160 and 161: 150 Boson Peak comparison of the ev
Page 162 and 163: 152 Boson Peak In figure 8.6 we sho
Page 164 and 165: 154 Boson Peak Predictions/explanat
Page 166 and 167: 156 Boson Peak meaning that the Deb
Page 168 and 169: 158 Boson Peak g(ω)/ω 2 [arb. uni
Page 170 and 171: 160 Boson Peak are equivalent becau
Page 172 and 173: 162 Boson Peak m P /m ρ 2 1.8 1.6
Page 174 and 175: 164 Boson Peak S(ω) [arb.unit] S(
Page 176 and 177: 166 Boson Peak 3 2.5 S(ω) [arb. un
Page 178 and 179: 168 Boson Peak perature effect on t
Page 181 and 182: Chapter 9 Summarizing discussion Wh
Page 183: 173 temperature in the harmonic app
Page 188 and 189: 178 BIBLIOGRAPHY Angell, C. A. [199
Page 190 and 191: 180 BIBLIOGRAPHY Casalini, R. and R
Page 192 and 193: 182 BIBLIOGRAPHY Farago, B., Arbe,
Page 194 and 195: 184 BIBLIOGRAPHY Inamura, Y., Arai,
Page 196 and 197: 186 BIBLIOGRAPHY Monaco, A., Chumak
Page 198 and 199: 188 BIBLIOGRAPHY Patkowski, A., Gap
Page 200 and 201: 190 BIBLIOGRAPHY Sekula, M., Pawlus
Page 203 and 204: Appendix A Details on the samples T
Page 205 and 206: A.1. Cumene 195 the value found fro
Page 207 and 208: A.2. PIB 197 The temperature depend
Page 209 and 210: A.4. DBP 199 peak differently at di
Page 211 and 212: A.6. Other samples 201 NH 2 tempera
Page 213 and 214: Appendix B Data compilations B.1 Da
Page 215 and 216: B.1. Data compilation 205 DHIQ = De
Page 217 and 218: B.1. Data compilation 207 Triphenyl
Page 219 and 220: Appendix C Dielectric setup Figure
Page 222: Abstract The degree of departure fr
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