Ph.D. thesis (pdf) - dirac

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of temperature and density for these dynamical properties themselves. It is especially
the combination of the density dependence of different dynamical quantities
presented here which is unique and interesting.
The report is structured as follows: Chapter 2 gives an introduction to the glass
transition phenomenology as studies at atmospheric pressure, including a short introduction
to the correlations that are considered in the later chapters. The phenomenology
of the alpha relaxation when studied under pressure is reviewed in the
first part of chapter 3, and the second part of chapter 3 deals with formulating how
pressure can be used to test correlations between fragility and other properties. The
principles of the experimental techniques, dielectric spectroscopy inelastic neutron
and inelastic X-ray scattering are found in chapter 4 where we also present the
background results used for treating the data. Chapters 5 to 8 present the experimental
results on the temperature and pressure dependences of different dynamical
properties. Each of these chapters has a section devoted to the proposed correlation
between the property in question and the fragility. Chapter 5 presents a study of the
relaxation time and spectral shape the alpha relaxation probed by dielectric spectroscopy.
Chapter 6 contains a study of the high Q collective modes measured by
inelastic X-ray scattering. The mean square displacement at the nanosecond time
scale measured by neutron backscattering is presented in chapter 7. The effect of
pressure on the boson peak is presented in chapter 8. The results of chapters 3 to 8
are finally combined, discussed and concluded on in chapter 9.
The samples we have used in the different experiments include a number of different
organic molecular liquids as well as polyisobutylene of different molecular weights.
The characteristic of the samples including their equation of state, data on fragility
and related dynamical properties are given in appendix A.