Microcanonical Analysis of Adsorption Transitions for Branching Polymer-Substrate Systems

The branching polymer–substrate system represents a hybrid interface where the central monomer of a polymer chain is grafted to a solid substrate. The presence of two subchains extending from the grafted monomer introduces additional structural complexity compared to end-grafted polymers. We employed the microcanonical inflection point analysis method to statistically study the phase behavior for a coarse-grained model of a flexible polymer centrally grafted to a continuous substrate. The density of states was obtained in extensive replica-exchange Monte Carlo simulations of the model and multi-histogram reweighting. Microcanonical statistical analysis of the entropy and its derivatives, combined with a detailed analysis of distance and contact maps, helped reveal distinct transitions between expanded, desorbed/adsorbed globular, and crystalline phases. Our results further contribute to the construction of a hyper-phase diagram parameterized by inverse temperature and surface interaction strength.