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Microstructure coarsening in phase-separated viscous liquids observed by in situ synchrotron microtomography
Phase separation concerns a wide range of liquids, from polymers to glass melts. In the coarsening regime, the typical size of phase separated domains grows with time in order to reduce interfacial energy. The kinetics of coarsening [Bray2002] are determined by physical properties of the liquids, but also by the topology of the phases, domains being either disconnected droplets or connected branches.
The goal of this study is to understand the local mechanisms of microstructure coarsening in phase-separated silicate liquids. To this aim, we performed in situ synchrotron micro- and nanotomography experiments at high temperature (850 to 1400°C), at the ESRF synchrotron. We used barium borosilicate glassy melts, for which the two phase-separated liquids have a strong (several orders of magnitude) viscosity contrast. On the ultrafast microtomography setup, 3-D images were acquired in a few seconds, for a voxel size of 1 micron. The parameters varied in our experiments are the viscosities (through temperature) of the liquids, and the volume fraction of the two phases. In order to retrieve morphological and topological information from noisy greyscale volumes, we developed a data processing workflow based on image denoising, phase segmentation, extraction of connected components and skeletonization of the percolating phases [scikit-image].
Our main result is the influence of the viscosity contrast on the morphology of the phases, and on their evolution [Bouttes2015]. A topological symmetry breaking arises as capillary breakups occur preferentially in the less viscous phase [Bouttes2016]. The percolating fluid phase is characterized by a universal distribution of lengths of branches, that results from successive breakups of branches, and subsequent coarsening of remaining branches. A fragmentation phenomenon is evidenced in the less viscous phase only, and leads to isolated droplets with a wide distribution of sizes [Bouttes2014].
[Bouttes2014] Bouttes, David, et al. "Fragmentation and Limits to Dynamical Scaling in Viscous Coarsening : An Interrupted in situ X-Ray Tomographic Study." Phys. Rev. Letters 112.24 (2014) : 245701.
[Bouttes2015] Bouttes, David, et al. "Hydrodynamic coarsening in phase-separated silicate melts." Acta Materialia 92 (2015) : 233-242.
[Bouttes2016] Bouttes, D., Gouillart, E., & Vandembroucq, D. (2016). Topological symmetry breaking in viscous coarsening. Physical Review Letters, 117(14), 145702.
[Bray2002] Bray, Alan J. "Theory of phase-ordering kinetics." Advances in Physics 51.2 (2002) : 481-587.
[scikit-image] Van der Walt, Stefan, et al. "scikit-image : image processing in Python." PeerJ 2 (2014) : e453.