The evolution of the demixing morphology in quasi 2D water-lutidine mixtures: a fractal dimension analysis

In this work, the evolution of the morphological properties of the liquid-liquid phase separation process of water-lutidine mixtures in a quasi-2D geometry locally heated by laser absorption is studied at different heating rates by videomicroscopy and complemented by a finite element simulation. Morphological changes of the separated domains are characterised using the fractal dimension and the distribution of domain sizes, capturing the main steps of the process: spinodal decomposition derived from the fluctuations in density at the critical point, separation into a bicontinuous structure, breaking of the structures producing a wide distribution of sizes, and the subsequent growth and coalescence of the demixed regions (domains) to produce a complete separation. A comparison with the simplest case of typical nucleation is made by performing the same analysis at a concentration where critical fluctuations are not present. We conclude that the methodology presented here can be used to characterise the main steps of the phase separation process and distinguish between spinodal decomposition and nucleation.