Étude spectrale de la lumière diffusée par les fluctuations thermiques de l'interface liquide vapeur de CO2 près de son point critique. mesure de la tension superficielle et de la viscosité

Abstract

Reçu le 10 avril 1974) Résumé. 2014 L'étude de l'évolution temporelle des fluctuations thermiques de l'interface liquide vapeur de CO2 près de son point critique Tc par analyse spectrale de la lumière diffusée, permet la mesure de la tension superficielle et de la somme des viscosités de cisaillement du liquide et de la vapeur (~ + ~'). Les résultats expérimentaux sont, dans le domaine de température 0,012 ~ Tc 2014 T ~ 12°C, compatibles avec 03B1 = 03B10(12014 T/Tc)03BC,03BC = 1,291 ± 0,023 et 03B10 = 95,1 ± 10,4. Nous avons comparé nos valeurs de (~ + ~') à celles que nous pouvons déduire des mesures de viscosité réalisées par des méthodes conventionnelles et trouvées dans la littérature. Pour Tc 2014 T 0,4 °C, nos mesures donnent des valeurs 10 à 20 % supérieures à celles-ci. Cet écart ainsi qu'une meilleure interprétation théorique des spectres expérimentaux expliquent que les valeurs de 03B1 mesurées ici ne sont pas tout à fait compatibles avec nos précédentes mesures. Abstract. 2014 We are studying the time evolution of fluctuations thermally excited at the liquidvapor interface of CO2 near its critical point by light scattering and light beating spectral analysis. This study allows the measurement of the surface tension 03B1 and of the sum (~ + ~') of the liquid and vapor shear viscosities. The experimental results are in fair agreement with 03B1 = 03B10 (1 2014 T/Tc)03BC, 03BC = 1.291 ± 0.023 and 03B10 = 95.1 ± 10.4 in the temperature interval 0.012 ~ Tc 2014 T ~ 12 °C. We compare our values for (~ + ~') with those we can deduce from viscosities found in the literature and obtained by conventional measurements. For Tc 2014 T 0.4 °C our results are 10 to 20 % larger. This difference and a better theoretical interpretation of our spectra explain why the values of 03B1 deduced from the present study do not exactly agree with our preceding measurements.

Fluctuations of elastic interfaces in fluids: Theory, lattice-Boltzmann model, and simulation

“…We also introduce the Fourier transform in time as It can be shown [52,53] that the frequency powerspectrum can be written in terms of the response function Γ k (ω) as…”

Thermal interface fluctuations of liquids and viscoelastic materials

“…Since the observed inclination of the surface is averaged within the beam spot, fluctuations with shorter wavelengths are effectively cutoff by a Gaussian factor. The spectral function for the thermal interface fluctuations between two fluids, described by densities ρ 1,2 , shear viscosities η 1,2 , and interface tension, σ has been derived in [13,14];…”

“…For the theory of thermal fluctuations of the agar/oil interface, we generalize the interface fluctuation formula Eq. (2) [13,14], by incorporating the polymer network contributions, as was done for the surface [15]. While this generalization has not been presented before, it is a natural one that can be derived much in the same manner [13][14][15].…”

“…(2) [13,14], by incorporating the polymer network contributions, as was done for the surface [15]. While this generalization has not been presented before, it is a natural one that can be derived much in the same manner [13][14][15]. Applying this theory, with the value of G used for the agar/air interface, w = 0.9 µm, and t = 24 • C, the computed spectrum matches excellently with the observed spectrum (Fig.…”

“…Using light scattering to observe thermal fluctuations is difficult for interfaces involving liquids with large viscosity, since the waves dissipate [10]. The theory of thermal fluctuations of interfaces was worked out from first principles some time ago [11][12][13][14][15], yet it had not been possible to experimentally examine their behavior in detail. In this work, the fluctuations are observed using light reflection, with the interface effectively acting as an optical lever [16][17][18][19], so that the method does not rely on the existence of waves that act as gratings.…”