How does flexibility shape anomalies in core-softened dimeric fluids?

Abstract

Many liquids display water-like anomalies—such as density maxima, diffusion anomalies, and nonmonotonic structural order—that originate from the competition between interaction ranges or local motifs. Isotropic core-softened (CS) models capture these effects but often neglect intrinsic anisotropy and internal flexibility. Here, we investigate how bond stiffness k reshapes anomalous behavior in dimeric CS fluids. By tuning k from highly flexible to effectively rigid, we show that rigidity shifts the temperature of maximum density , narrows the diffusion anomalies to lower temperatures, and modifies the structural order. Most importantly, increased stiffness introduces emergent geometric length scales in the center-of-mass radial distribution function. In the rigid limit, the anisotropy-induced peak at r ≃ 1.5 overtakes the intrinsic CS feature at r ≃ 1.2, reorganizing the hierarchy of relevant distances. This three-scale competition (two radial and one geometric) provides a unified explanation for the correlated shifts of anomalies across the P–T plane, establishing bond stiffness as a key control parameter to tune anomaly-driven behavior in anisotropic soft matter.