Exploring the Interplay between Local Chain Structure and Stress Distribution in Polymer Networks

The mechanical behavior of polymer networks is intrinsically correlated with the local chain topology and chain connectivity.In this study,we delve into this relationship through the lens of coarse-grained molecular dynamics(CG-MD)simulations.Our aim is to illuminate the intricate interplay between local topology and stress distribution within polymer monomers,cross-linkers,and various components with distinct cross-link connections,thereby elucidating their collective impact on the mechanical properties of polymer networks.We mainly focus on how specific local structures contribute to the overall mechanical response of the network.In particular,we employ local stress analysis to unravel the mechanics of these structures.Our findings reveal the diverse responses of individual components,such as junctions,strands,cross-linkers between junctions,and dangling chain ends,when subjected to stretching.Notably,we observe that these components exhibit varying degrees of deformation tolerance,underscoring the significance of their roles in determining the mechanical characteristics of the network.Our investigations highlight junctions as primary contributors to stress accumulation,and particles with higher local stress showing a stronger correlation between stress and Voronoi volume.Moreover,our results indicate that both strands and cross-linkers between junctions exhibit heightened stress levels as strand lengths decrease.This study enhances our understanding of the multifaceted factors governing the mechanical attributes of cross-linked polymer systems at the microstructural level.

The Crystallization Behavior Regulating Nature of Hydrogen Bonds Interaction on Polyamide 6,6 by Poly(vinyl pyrrolidone)

The crystallization behavior of polyamide 6,6(PA66) under complex flow field is of great importance for its final mechanical properties.Poly(vinyl pyrrolidone)(PVP) was applied as crystallization modifying agency to improve processability of PA66.The regulation nature on hydrogen bonds(H-bonds) interaction of PVP was studied upon cooling process.As revealed by in situ FTIR,the sample with 5 wt% PVP displays decreased enthalpy change(ΔH) for both the generation of H-bonds and the transition of H-bonds from “disordered” to “ordered” state,which illustrates the molecular mechanism for the regulation of crystallzation behavior.Moveover,2D-WAXD is applied to reveal the evolution of microstructure for sample under external injection field.Hermans orientation factor(f_(H)) decreases obviously with the addition of PVP,because the relaxation of chain segments is promoted as well the crystallization is retarded.The above crystallization and microstructure changes during the processing provokes the improvement of processability without the apparent sacrifice of mechanical properties.