Correlation of PEO conformations and solvation in PEO-NaSCN polymer electrolytes

The polymeric conformations can provide insight into the structure and the mechanism of ion transport in solid polymer electrolytes. In this work, the FT-IR spectra of PEO-NaSCN complexes were measured at room temperature, and the solvation of NaSCN in PEO was revealed by the conformational changes of PEO with NaSCN content. It is suggested that the complexation of PEO with NaSCN can occur through three modes: trans-coordination, gauche-coordination, and cryptande-coordination, depending on the conformation and the flexibility of PEO backbone. The trans-coordination is a weak solvation and can cause the interchain crosslinking and the reduction of segmental motion. The gauche-coordination is a strong complexation and can form complexes in which Na+ is wrapped by the PEO helix. The cryptandes result from the internal rotation of the flexible PEO backbone and can interact directly with NaSCN to form triple ion aggregations, especially when the salt content is low in PEO. In addition, the effect of PEO crystallinity on solvation and the solvating ability of PEO with different molecular weight are discussed also in this paper.