Fragmentation and Limits to Dynamical Scaling in Viscous Coarsening: An Interruptedin situX-Ray Tomographic Study

Abstract

X-Ray microtomography was used to follow the coarsening of the structure of a ternary silicate glass experiencing phase separation in the liquid state. The volumes, surfaces, mean and Gaussian curvatures of the domains of minority phase were measured after reconstruction of the 3D images and segmentation. A linear growth law of the characteristic length scale ∼ t was observed. A detailed morphological study was performed. While dynamical scaling holds for most of the geometrical observables under study, a progressive departure from scaling invariance of the distributions of local curvatures was evidenced. The latter results from a gradual fragmentation of the structure in the less viscous phase that also leads to a power-law size distribution of isolated domains.Introduction -The construction of a theoretical framework describing the phase separation of binary liquids [1][2][3] has been fueled by successive experimental developments. Up to the 90's, most experimental observations were performed in the Fourier space, with light or neutron scattering. Model systems were immiscible solutions [4,5], and polymer blends [6,7], or glasses [8]. These experiments confirmed that the dynamical scaling assumption is relevant for these systems, i.e. it is possible to rescale the structure factor by a unique length scale . This length increases with a power law: (t) ∼ t α , α depending on the growth regime [9]. More recent numerical simulations confirmed this scaling behavior, and provided some insights about the geometry in real space [10][11][12]. Meanwhile, access to direct space was made possible by new techniques of observation, such as scanning laser confocal microscopy: curvatures could be measured on phase-separated polymer blends [13,14]. These observations are especially relevant to discuss the local mechanisms that govern the coarsening: pinch-off was for instance observed in a colloidal glass [15]. Recent predictions concerning statistical quantities such as size or surface distributions of domains [16,17] and numerical studies of aging in phase-separating fluids [18,19] also motivate the observation in real space.The effect of the mobility on the morphology has recently raised a growing interest. Experiments on polymers revealed the spectacular influence of visco-elasticity [20]. Recent work [21] evidenced a logarithmic (stressassisted) growth for a gas-glass phase separation. Numerical simulations with a viscosity contrast [22,23] showed a strong effect on morphology. However, the influence of a sole viscosity contrast has not yet been experimentally investigated in the hydrodynamical regime.The development of X-ray microtomography provides an suitable tool to explore phase separation in 3-D, with submicron spatial resolution reached in Synchrotron facilities [24,25]. Phase-separated polymer blends were

Structure and viscosity of phase‐separated BaO–SiO2 glasses

“…Although compositions near the center of the miscibility gap (~10 mol% BaO) result in a highly interconnected substructure, Seward et al suggested that this phase separation whose final morphology resembles that of a spinodal decomposition presumably occur by a nucleation‐and‐growth mechanism, followed by the coalescence of discrete second‐phase particles into the interconnected micro/nano‐structure. Another plausible mechanism was brought to light by a recent in situ X‐ray tomography study of the phase separation process in a SiO 2 (57.1 mol%)–BaO(23.3 wt%)–B 2 O 3 (18.9 wt%) . In this latter study, it was proposed that phase separation stems from the viscous coarsening of a bi‐continuous structure, followed by the fragmentation of the less viscous phase to produce isolated domains.…”

Coarsening phenomena

“…X-ray tomography, a way to observe slices of the sample in a progressive and non-destructive manner, was used to quantify phase separating glass-forming liquid binary mixtures [25]. Among many other interesting features, this study showed that, unexpectedly, this system evolves in a diffusive hydrodynamic regime.…”

Probing Colloidal Gels at Multiple Length Scales: The Role of Hydrodynamics

“…Gels can be soft or biological materials such as proteins [5,6], clays [7], foods [8], hydrogels [9], and tissues [10,11]. However, a more diverse range of systems including granular matter [12], phase-demixing oxides [13], and metallic glassformers [14] also exhibit gelation. The mechanical properties of gels are influenced by their structure both locally [15][16][17][18] and at a global level through percolation of particles [19] and clusters [20], network topology [21], and confinement [22].…”