ma9b01963_si_001.pdf (5.05 MB)
Structure and Properties of Bicontinuous Microemulsions from Salt-Doped Ternary Polymer Blends
journal contribution
posted on 2019-12-13, 15:47 authored by Shuyi Xie, Daniel J. Meyer, En Wang, Frank S. Bates, Timothy P. LodgeWe have systematically examined the phase behavior of
lithium salt-doped
A/B/AB ternary polymer blends
composed of low-molar-mass poly(ethylene oxide) (PEO) and polystyrene
(PS) homopolymers, a symmetric PS-b-PEO block copolymer
(SO), and lithium bis(trifluoromethane) sulfonimide (LiTFSI) by a
combination of small-angle neutron scattering and small-angle X-ray
scattering, bolstered by ionic conductivity measurements. The salt
partitions exclusively to the PEO and acts to increase the segregation
strength of the blends, leading either to macroscopic or microscopic
phase segregation. By constraining the volume fractions of the two
homopolymers to be the same (ϕPEO+LiTFSI/ϕPS = 1), a two-dimensional phase diagram along the volumetrically
symmetric isopleth of the phase prism has been mapped out, and a well-structured
bicontinuous microemulsion (BμE) is found over a wider range
of total homopolymer composition (ca. ϕH ≈
80–86%), compared to the neutral polymer case, where a 1–3%
range in ϕH is typical. The characteristics of the
BμE are obtained via the Teubner–Strey structure factor
and are tunable by ϕH, temperature, and salt concentration.
Moreover, the BμE possesses superior ionic transport properties,
demonstrating higher conductivity compared to both microphase-separated
(lamellar) and nonstructured disordered blends. This work offers a
strategy to obtain well-defined microstructured ion-containing polymer
systems with tunable co-continuous morphology and favorable conductivity
properties, which could help optimize the design of polymer electrolytes.