Density fluctuation analysis very near above and below critical point using morphological and spatiotemporal information

Ana Oprisan (1) , Sorinel Oprisan (1) , Yves Garrabos (2) , Carole Lecoutre-Chabot (2) , Daniel Beysens (3)

1 Department of Physics and Astronomy [Charleston]
2 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
3 PMMH - Physique et mécanique des milieux hétérogenes (UMR 7636)

We investigate the fractal nature of critical fluctuations in sulfur hexafluoride (SF6) under microgravity conditions. For this purpose, we use the Bidimensional Empiric Mode Decomposition (BEMD) approach to separate the spatial scales of fluctuations in orthogonal Independent Mode Functions (IMFs). Statistical analysis of three morphology measures (area, eccentricity, and orientation of convex objects in recorded images) across different IMFs shows that critical fluctuations obey power-laws across multiple spatial scales. We also perform a spatiotemporal analysis of fluctuations by extracting one line of pixels from each image and creating a temporal stack from successive images, or “waterfalls.” The spatiotemporal section analysis along the spatial direction reveals multiple spatial scales present in the original fluctuating image. The analysis of the “waterfalls” along the temporal direction identifies a common power-law temporal behavior across all spatial scales. Our results show that critical fluctuations very near critical temperature (Tc) have a fractal structure captured by power-laws with multiple critical exponents. The morphology analysis shows that very near Tc, the fluctuating domains are mostly spherical with some anisotropy.

Domaines: Matériaux

Ana Oprisan, Sorinel Oprisan, Yves Garrabos, Carole Lecoutre-Chabot, Daniel Beysens. Density fluctuation analysis very near above and below critical point using morphological and spatiotemporal information. The European Physical Journal Plus, 2021, 136 (5), 523 (17 p.). ⟨10.1140/epjp/s13360-021-01531-8⟩. ⟨hal-03230780⟩