The infinite dilution radii of gyration (Rg,0) for five different molecular weights (10-250 kg/mol) of perdeuterated poly(ethylene oxide) (d-PEO) have been determined at 80 °C in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) using small-angle neutron scattering (SANS). The results establish the dependence of Rg,0 on polymer molecular weight as Rg,0 ∼ Mw0.55. An excluded volume exponent of ν ≈ 0.55 indicates that [BMIM][BF4] is a moderately good solvent and that PEO remains a flexible random coil in this ionic liquid. These results clarify the uncertainty surrounding PEO coil dimensions in this ionic liquid, as computer simulations at various levels of complexity have led to conflicting results, and prior experimental results also do not present a completely consistent picture.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation (DMR-1707578). Portions of this work were performed at the DuPont−Northwestern−Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. Data were collected using an instrument funded by the National Science Foundation under Award 0960140. SANS experiments were conducted on NG-7 30 m and NG-B 30 m SANS instruments in National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). We specifically thank Dr. Yimin Mao and Dr. Paul Butler for their assistance in SANS measurements and data analysis. We also acknowledge the help of Dr. Dan Zhao for insightful discussions and Peter Schmidt for taking the MAXS measurements.
© 2017 American Chemical Society.