Hydrodynamic singularities mimic criticality in dewetting polymer films

Dewetting of polymer thin films on nonwettable substrates culminates in a late-stage morphological transition in which a connected fibrillar network fragments into isolated droplets. Because this transformation resembles a depercolation process, it raises the question of whether the network-droplet transition represents a genuine critical phenomenon. We address this question by defining a connectivity-based order parameter and analyzing spatial correlations of the evolving morphology. Although the order parameter exhibits a sharp decrease suggestive of critical behavior, the correlation length of the polymer-rich phase remains finite, evolves through irregular fluctuations, and shows no divergence near the transition. We explain this by noting that the length scales at which the Plateau-Rayleigh instabilities act are much smaller than the large-scale correlations encapsulated in the structure's correlation length. In addition, nondimensionalized order-parameter curves measured at different observation scales fail to collapse onto a universal master curve. These results demonstrate that the breakup of the fibrillar network is governed by localized Plateau-Rayleigh rupture events rather than system-spanning cooperative dynamics. The late-stage transition in dewetting films therefore mimics a hydrodynamic singularity-driven pseudocritical crossover rather than a true critical transition.