Composite electrolytes comprising polytetramethylene/polypropylene glycol-based waterborne polyurethanes and polyethylene oxide via a mixture design approach

The composite electrolytes (CEs) were prepared by impregnating the ternary composites comprising polypropylene glycol-based waterborne polyurethane (denoted as WPU(PPG)), polytetramethylene glycol-based waterborne polyurethane (denote as WPU(PTMG), and polyethylene oxide (PEO) with LiClO₄/PC. The data of the swollen weight (S_w) and the room-temperature conductivity (σ₂₅) for CEs were fitted as empirical regression equations by using mixture design. These empirical equations were used to construct contour plots, facilitating comparisons of synergistic/antagonistic effects among the mixed polymers. The contour plots show that the maximum S_w (64.3%) appears at point X₃ (PEO 95% and WPU(PPG) 5%), while the maximum σ₂₅ (≈10^-3 S/cm) appears in a wide region (WPU(PPG) = 5-43%, WPU(PTMG)<37%, and PEO>27%). Differential scanning calorimetry (DSC) results showed immiscibility between WPU(PTMG) and PEO and partial immiscibility between WPU(PPG) and WPU(PTMG)/ PEO. A polarized micrograph (PM) of the composites was also examined for PEO spherulites. The contour plot results of S_w and σ₂₅ can be explained by the interactions among polymers on the basis of their molecular structures, also evidenced by both DSC and PM results.