Contents · i

1 Introduction — 1

2 Theoretical Foundations of Critical Phenomena in Liquids — 5

2.1 Phase Transitions in Thermodynamic Systems — 5

2.1.1 Phase Transitions in General — 5

2.1.2 Phase Transitions According to Ehrenfest — 6

2.1.3 Liquid–Liquid Phase Transition (Binary Liquid Mixtures with a Miscibility Gap) — 8

2.2 Critical Phenomena — 11

2.2.1 Critical Exponents and Order Parameters — 11

2.2.2 Static Scaling Hypothesis — 12

2.2.3 Dynamic Scaling Hypothesis — 14

3 Theory of the Measurement Methods and Quantities Considered — 17

3.1 Ultrasound Spectroscopy — 17

3.1.1 Sound Absorption in Liquids — 19

3.1.1.1 Classical Attenuation — 19

3.1.1.2 Excess Attenuation — 22

3.1.1.3 Critical Attenuation — 24

3.2 Light Scattering — 29

3.2.1 Electromagnetic Scattering Theory — 29

3.2.2 Scattering Spectrum of a Liquid — 32

4 Experimental Implementation — 37

4.1 Principle — 37

4.2 Resonators: Measurement Range 15 kHz to 20 MHz — 37

4.2.1 Ideal and Real Resonators — 38