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168 Boson Peak perature effect on the alpha relaxation. We stress that the interpretation above is a suggestion based on the very limited knowledge of the pressure dependence of the boson peak intensity. More studies would be needed to verify this interpretation. It is clear that the correlation, if present at all, is a trend rather than a one to one correlation between fragility and R. The most prominent outlier in figure 8.11 and particularly in figure 8.12 is sorbitol. In figure 8.20 we show the S(ω) of sorbitol at T g . The peak is remarkably different from the boson peak in the other systems we have studied. The boson peak energy is a factor 2 larger, and the shape is also distinctively different. Sorbitol is a hydrogen bonded system. This suggests that the boson peak is different in a hydrogen bonded system as compared to other molecular liquids. 8.4 Summary This chapter has two main sections. The first section contains a study of the boson peak under pressure in glassy PIB (M w =3580g/mol). We find i) that the boson peak energy increases faster with pressure than any of the other modes. ii) that intensity of g(ω)/g D (ω) increases with pressure. iii) the shape of the boson peak seen in the rDOS g(ω)/ω 2 is unaffected by pressure. The decrease in the low frequency intensity seen directly in the rDOS (figure 8.5) has earlier been used to favor the interpretation that the shift in the boson peak is due to a suppression of specific modes rather than a shift of modes to higher frequencies [Gurevich et al., 2005; Hizhnyakov et al., 2000; Klinger, 1999, 2001; Inamura et al., 2000, 2001]. Our results are in clear contradiction with this view, as we do not see a suppression of modes. It has recently been suggested by Monaco et al. [2006 b] that the changes in boson peak due to pressure could be explained entirely by the pressure induced increase in the macroscopic force constants, and that they would disappear when normalizing to the Debye frequency and the amplitude of the Debye density of states. This is clearly not the case for the pressure dependence of the boson peak in PIB. The second part of this chapter deals with proposed correlation between the fragility and the parameter R. This parameter is given by the intensity of the quasi-elastic scattering (plus the Debye level) relative to that of the boson peak evaluated at T g . We test this correlation on a set of samples which span a large range in isobaric as well as isochoric fragility. In both cases we find a somewhat scattered correlation. We moreover find that the parameter R is constant along the glass transition isochrone
8.4. Summary 169 as is also the isochoric fragility. Based on this observation we suggest that the correlation to isochoric fragility is more fundamental. This indicates that the R could be related to the pure effect of temperature on the relaxation time rather than that of density. We note that the pressure dependence of R and the pressure dependence of the inverse boson peak intensity in terms of g D (ω)/g(ω) are different. The first is independent of pressure while the latter decreases with pressure. We moreover note that it is seen directly from the raw data that the value of R is largely controlled by differences in the intensity of the quasi-elastic scattering. This leads us to speculate that the correlation with fragility (if present at all) is related to the amplitude of the quasi-elastic scattering rather than the amplitude of the boson peak.
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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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Page 127 and 128: 6.5. Summary 117 d log (e(ρ))/ d l
Page 129: Résumé du chapitre 7 Dans ce chap
Page 132 and 133: 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 181 and 182: Chapter 9 Summarizing discussion Wh
Page 183 and 184: 173 temperature in the harmonic app
Page 185: Chapter 10 Perspectives In this wor
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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