Characterizing tie molecules during strain-induced structural reconstruction of polymer network incorporating nanocrystalline regions

Tie molecules and chain entanglements, as well as the distribution of crystalline and amorphous regions, play critical roles in determining mechanical properties of semicrystalline materials. Cyclic stretching and compressing of the material can be further used to tune microstructures and mechanical properties. Herein, we characterize the distribution of crystalline domains, tie molecules, entanglements and folds in polyvinyl alcohol (PVA) networks under cyclic stretching. We use the coarse-grained molecular dynamics approach developed in (Meyer et al, J. Chem. Phys. 2001). We focus on polymer networks with nanocrystalline regions, which in experiments can be realized via freeze-thawing. It was shown that cyclic pre-stretching of freeze-thawed PVA hydrogels lead to the significant improvement of mechanical properties including fatigue resistance of these materials (Lin et al, PNAS 2019). We quantify the effect of strain rate on fraction of tie molecules and entanglements and on the distribution of the crystalline domains. Our study highlights the role tie molecules play during the stretching of the polymer network incorporating crystalline and amorphous regions.