(129e) A Study of the Thermodynamics of PEO/PMMA/Litfsi Blend Electrolytes | AIChE

(129e) A Study of the Thermodynamics of PEO/PMMA/Litfsi Blend Electrolytes


He, L., Oak RIdge National Laboratory
Gao, K. W., University of California, Berkeley
Balsara, N. P., University of California, Berkeley
Shalaby, M., New York University
Garetz, B. A., New York University
In this study, we examined the thermodynamics of added salt on a miscible polymer blend system. Our system of interest was Poly(ethylene oxide)/Poly(methyl methacrylate)/ Lithium bis(trifluoromethanesulfonyl)imide or PEO/PMMA/LiTFSI. We added LiTFSI to PEO (8.5 kg/mol) and PMMA (47.3 kg/mol) to create a series of blends. We studied 5 blends: two PEO-rich blends, two PEO-lean blends and one symmetric blend. We utilized small angle neutron scattering (SANS) to determine the phase behavior. We found that the two PEO-rich blends were miscible in both the neat state and at all salt concentrations. We found that the PEO-lean blends were only miscible in the neat state and were immiscible when salt was added. Most unusually, we found that the symmetric blends were completely miscible except at r = 0.05, where r is the moles of lithium per moles of ethylene oxide. This initial phase behavior pointed to a highly complex relationship between blend composition, salt concentration and miscibility. We utilized the framework of de Gennes random phase approximation to calculate an effective χ parameter (χeff) from the scattering profiles. We found that χ for neat blends has a linear dependence on composition and were able to analyze these parameters using the theoretical framework of Sanchez. We found that χeff is a non-linear function of composition for the salt containing samples, in contrast with the neat samples. The results from this study indicate that the thermodynamics in a polymer blend electrolyte system are a strong, non-linear function of blend composition and salt concentration.