This manuscript details
a novel and simple approach to achieve
surface-tethered co-poly(ionic liquid) (coPIL) films through the exchange
of the resident anion of a poly(ionic liquid) (PIL) film with two
or more anions. Initially, surface-tethered PIL films were prepared
by the surface-initiated ring-opening metathesis polymerization of
the ionic liquid monomer 3-[(bicyclo[2.2.1]hept-5-en-2-yl)methyl]-1,2-dimethylimidazol-3-ium
hexafluorophosphate ([N
1
-dMIm][PF
6
]) whose PF
6
–
anion was easily interchanged with aqueous
solutions containing a binary mixture of the PF
6
−
anion, along with perchlorate (ClO
4
−
) or bis(fluorosulfonyl)imide (FSI
−
) anions. The
binary mole fraction of each anion in the film was determined from
the infrared spectra of the coPIL films. The thermodynamically driven
anion selectivity for exchange from the liquid phase into the coPIL
films was determined to follow the order ClO
4
–
< PF
6
–
< FSI
–
. The aqueous wettability of p[N
1
-dMIm] coPIL films containing
both the PF
6
–
and ClO
4
–
anions (p[N
1
-dMIm][PF
6
][ClO
4
]) was quantified by contact angle goniometry with the observation
that the surface showed an enrichment in the ClO
4
–
anion compared to the average binary anion mole fraction of ClO
4
–
in the film (
y
ClO
4
–
). The rate of ion transport through
the p[N
1
-dMIm][PF
6
][ClO
4
] coPIL films,
quantified by electrochemical impedance spectroscopy, linearly depends
on the binary anion mole fraction of ClO
4
–
in solution (
x
ClO
4
–
), enabling continuous tunability by over three orders of magnitude
for ion conductivity in the coPIL films.