Counterion condensation or lack of solvation? Understanding the activity of ions in thin film block copolymer electrolytes

Abstract

Dissociation of ion charge pairs in block copolymer electrolytes and its relation to activity coefficients and normalized ionic conductivity.

Understanding the ionic activity and conductivity value differences between random copolymer electrolytes and block copolymer electrolytes of the same chemistry

“…The procedure to prepare interdigitated electrodes (IDEs), BCE thin lms, as well as methods for thin lm characterization (e.g., solution uptake/water via QCM, ion sorption, environmental GI-SAXS, and ionic conductivity using IDE substrates) are documented in our previous report. 31 More specically, solution uptake (SU) experiments were performed using a Gamry e-chem quartz crystal microbalance (QCM) where the BCE and RCE thin lms were prepared on gold quartz crystals. These crystals were then loaded into the QCM chamber and a KI aq solution was added so that the thin lms were submerged in the solution.…”

“…The equations and methods for calculations are provided in our previous report. 31 GI-SAXS experiments were performed at the Advanced Photon Source (APS) Beamline 8-ID-E at Argonne National Laboratory. The beamline was equipped with an environmental chamber and the BCE thin lms self-assembled on Si wafers, were covered with KI aq droplets.…”

“…13,36 Thin lm RCEs were prepared in a similar fashion to thin lm BCEs described in our previous work. 31 More specically, a 1.5 wt% solution of PSrP2VP in toluene was prepared and spincoated (4000 rpm for 45 seconds) onto a Si wafer, gold quartz crystals or IDEs. Aer spin coating the RCP on the substrate, the sample was exposed to 200 C for 10 minutes under a dry nitrogen gas.…”

“…Aer graing the PSrP2VP brushes to the substrate, PSbP2VP 40-44k, PSbP2VP 102-97k or P2VPbPSbP2VP 12-23-12k was spincoated on the substrates and then solvent annealed with acetone to make perpendicular lamellae structures. 31 Aerwards, the thin lm random copolymer and block copolymer samples were exposed to CH 3 I vapor for 24 hours in a 125 mL wide mouth jar. This exposure alkylated the nitrogen in the pyridine ring of the polymers to prepared n-methyl pyridinium iodide groups (i.e., xed charge groups) without disrupting the nanostructure of the BCPs and forming RCE and BCE samples.…”

“…However, Manning's theory does not always yield accurate values (e.g., peruorosulfonic acid membranes exposed to concentrated acid solutions). 30 In our previous work, 31 we reported a multitude of techniques, such as a quartz crystal microbalance (QCM), environmental grazing incidence small-angle X-ray scattering (GI-SAXS) and molecular dynamics (MD) simulations, for probing ionic activity in a model thin lm block copolymer electrolyte composed of poly(styrene-block-2 vinyl pyridine-co-n-methyl pyridinium iodide) (PSbP2VP/NMP + I À ). The activity coefficients of this thin lm BCE in the osmotic-controlled regime 32 were found to be low, but 90% of the ions did exert activity in this regime (i.e., a small contingent of condensed counterions that do not exert activity).…”