Coil dimensions of poly(ethylene oxide) in an ionic liquid*

The combination of polymers and ionic liquids (ILs) provides a platform for designing materials with tunable properties that have a wide range of applications. However, the use of these materials would benefit from a thorough understanding of the polymer behavior in ILs, and in particular the dimensions of polymer chains in ILs. Recently, a number of simulations and experimental studies have reported conflicting findings with respect to the radius of gyration of varying chain lengths of poly(ethylene oxide) (PEO) in an IL. In order to elucidate such discrepancies, direct measurements of coil size is desirable; however, the similarity in refractive indices of PEO and ILs limits the use of techniques such as light scattering. We therefore employ small-angle neutron scattering (SANS) to assess coil dimensions of varying molecular weights of perdeuterated PEO in an IL. Our results indicate that PEO chains behave as flexible random coils that are moderately swollen in the IL of interest; the Flory exponent ν ≈ 0.55. This experimental work therefore clarifies the uncertainties surrounding the dimensions of PEO coils in IL, and can help benchmark better simulation models and relevant experiments.