Trimodal defect height distribution during morphological phase separation in thin liquid films of thickness-dependent...

Morphological phase separation (MPS) of the thin liquid film is a complex interplay of intermolecular forces, hydrodynamic instability, and fluid properties. This study investigates the influence of thickness-dependent viscosity (liquid film viscosity decreases with an increase in film thickness) on the MPS in thin liquid film by incorporating inhomogeneous rheology. Based on the continuum hydrodynamic model with non linearly dependent viscosity function of local thickness, we numerically simulate the pattern formation dynamics over a broad time range. Our results show that the early and late phase separation stages conform to classical spinodal behaviour but the intermediate phase separation stage exhibits sub-spinodal behaviour due to rheological inhomogeneity. The intermediate phase separation stage reveals the emergence of sub-spinodal lengthscales through the formation of satellite defects between already growing primary defects if the mobility in thinner regions is very low. It also highlights trimodal defect height distribution, in contrast to the generally observed bimodal distributions in homogeneous viscosity films.