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

LB Krott and TPO Nogueira and DFK Silva and JR Bordin, JOURNAL OF CHEMICAL PHYSICS, 163, 174908 (2025).

DOI: 10.1063/5.0300142

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 similar or equal to 1.5 overtakes the intrinsic CS feature at r similar or equal to 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.

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