Avrami Kinetics of Cylindrical Growth Under Hard-Wall Confinement: A Monte Carlo Study of Thin Film Crystallization

The Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism provides a classical framework for describing polymer crystallization kinetics; its applicability under finite-domain confinement requires quantitative assessment. In this work, the influence of one-dimensional geometric restriction on cylindrical growth in polymer thin films is investigated using a stochastic Monte Carlo approach. The model considers site-saturated nucleation on randomly distributed cylindrical nanofibers with constant radial growth velocity under hard-wall boundary conditions. Crystallization kinetics were evaluated through automated segmented regression of the double-logarithmic JMAK representation. Under confinement, the Avrami plot departs from single-slope linearity and exhibits two successive quasi-linear regimes characterized by effective parameter pairs (n₁, ln k₁) and (n₂, ln k₂). The primary exponent n₁ remains thickness-independent, consistent with early-stage radial expansion prior to boundary interaction. The secondary exponent n₂ displays a non-monotonic dependence on reduced film thickness, reflecting the competing influence of wall-induced truncation and inter-fiber impingement on late-stage transformation. These results support a geometric interpretation in which finite-domain constraints modify effective growth dimensionality and provide a reproducible framework for analyzing dual-regime Avrami behavior in confined crystallization systems.