Conformation of poly(ethylene oxide) dissolved in ethylammonium nitrate

Small angle neutron scattering has been used to investigate the morphology of 38 kDa PEO dissolved in ethylammonium nitrate (EAN) in the dilute and semidilute concentration regions. At infinite dilution, the radius of gyration, R_g, is 8.1 nm. This value decreases through the dilute regime according to a concentration (c) dependence of R_g ≈ c^-0.24, while above the overlap concentration a c^-1 dependence is followed. These values differ from aqueous solution behavior, which we attribute to EAN being a poorer solvent for PEO than water; EAN is in fact close to a θ solvent. The polymer structure on length scales less than 3 nm is unaffected by increasing polymer concentration, suggesting that the overall decrease in coil dimensions is a consequence of tighter packing of ~3 nm polymer “blobs” into a smaller volume.