Abstract
Both the mesoscopic structure (as seen by small angle neutron scattering) and the dynamics (as seen by neutron spin echo technique) of the critical fluctuations were measured in CO2 close to the liquid-gas phase transition. The static aspects of the critical behavior of CO2 were first measured on the critical isochore for reduced temperature from 6 10−5 to 6 10−2 (t = (T-Tc)/Tc, Tc the critical temperature) allowing to characterize precisely the critical behaviour of the correlation length ξ of the density fluctuations. Then, the dynamics was probed over the Q-interval 0.025–0.21 Å−1 for correlation lengths ξ ranging between 10 Å and 400 Å. Neutrons are well suited for studying the critical regime (Qξ ≫ 1) and the crossover region between the hydrodynamic and critical regimes (Qξ∼1). The measured widths of the Rayleigh line for values of Qξ ranging from 0.3 to 32 are in very good agreement with the Kawasaki function proposed to describe the crossover.
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References
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Leclercq, F., Pouget, S., Damay, P. (2002). Critical Slowing Down in a Simple Fluid System as Measured by Neutron Spin Echo Technique. Crossover Between Hydrodynamics and Critical Dynamics. In: Mezei, F., Pappas, C., Gutberlet, T. (eds) Neutron Spin Echo Spectroscopy. Lecture Notes in Physics, vol 601. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-45823-9_19
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DOI: https://doi.org/10.1007/3-540-45823-9_19
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