Salt Doping In PEO Containing Block Copolymers: Counterion and Concentration Effects

We describe the phase behavior of poly(styrene-b-ethylene oxide) block copolymers doped with various salts. We studied these block copolymers over a range of EO:ion ratios using small-angle x-ray scattering (SAXS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) experiments. Samples were rigorously dried and prepared in an argon atmosphere to reduce the effects of moisture uptake on phase behavior (especially for SAXS samples). We found that both the salt counterion and the salt concentration in the poly(ethylene oxide) block influence the nanoscale domain spacing and polymer morphology in a controllable fashion. Additionally, doping with salts led to thermal order-order transitions that could be rationalized based on the crystallization of the PEO-salt complexes.