arXiv subjects

Stéphane Parola

Publications and source records attributed to Stéphane Parola.

2 recordsLinked to original sources

arXiv2026

Structural color palette of disordered colloids in the Rayleigh scattering regime

Structural coloration by Rayleigh scattering is widespread in nature and holds a prominent place in various art objects over a broad period of time. Beyond the common statement that Rayleigh scattering is the primary mechanism behind the multiple colored appearances of the sky, it appears that the relationship between material parameters and the colors appearing in different observation conditions has not been thoroughly explored so far. This study provides a comprehensive overview of Rayleigh scattering-based structural colors as functions of key material properties, and introduces a scalable, environmentally friendly method to fabricate solid composites with targeted colors in both reflection and transmission. Monte Carlo light transport simulations are performed to compute the structural color palette of disordered colloids -- dielectric particles in a nonscattering matrix -- in different observation modes. We provide a range of physical parameters in which the materials exhibit the same blue color in diffuse reflection and transmission. We also show that, counterintuitively, the addition of black absorbents to the matrix of a white (opaque) material can lead to the emergence of a blue coloration in diffuse reflection, thanks to the interplay between multiple scattering and absorption. Our predictions are validated by optical experiments on colloidal suspensions of Yttria-stabilized Zirconia (ZrO$_2$:Y$_2$O$_3$) nanoparticles in aqueous solutions. The potential of Rayleigh-scattering materials for visual arts and design is further supported by realizing solid-state composites based on abundant materials, namely borosilicate clays and hybrid silica-based glasses, using soft chemistry at room temperature.

physics.optics↗

arXiv2023

Shear-induced reinforcement in boehmite gels: a rheo-X-ray-scattering study

Boehmite, an aluminum oxide hydroxide $γ$-AlO(OH), is broadly used in the form of particulate dispersions in industrial applications, e.g., for the fabrication of ceramics and catalyst supports or as a binder for extrusion processes. Under acidic conditions, colloidal boehmite dispersions at rest form gels, i.e., space-spanning percolated networks that behave as soft solids at rest, and yet yield and flow like liquids under large enough deformations. Like many other colloidal gels, the solid-like properties of boehmite gels at rest are very sensitive to their previous mechanical history. Our recent work [Sudreau et al., J. Rheol. 66, 91-104 (2022), and Phys. Rev. Material 6, L042601 (2022)] has revealed such \textit{memory effects}, where the shear experienced prior to flow cessation drives the elasticity of boehmite gels: while gels formed following application of a shear rate $\dotγ_{\rm p}$ larger than a critical value $\dotγ_{\rm c}$ are insensitive to shear history, gels formed after application of $\dotγ_{\rm p}<\dotγ_{\rm c}$ display reinforced viscoelastic properties and non-negligible residual stresses. Here, we provide a microstructural scenario for these striking observations by coupling rheometry and small-angle X-ray scattering. Time-resolved measurements for $\dotγ_{\rm p} <\dotγ_{\rm c}$ show that scattering patterns develop an anisotropic shape that persists upon flow cessation, whereas gels exposed to $\dotγ_{\rm p}>\dotγ_{\rm c}$ display isotropic scattering patterns upon flow cessation. Moreover, as the shear rate applied prior to flow cessation is decreased below $\dotγ_{\rm c}$, the level of anisotropy frozen in the sample microstructure grows similarly to the viscoelastic properties, thus providing a direct link between mechanical reinforcement and flow-induced microstructural anisotropy.

cond-mat.soft↗