posted on 2022-01-19, 05:13authored byQuan Yang, Qi Zhang, Shenlin Zhu, Weibin Cai
In
this study, we prepared a composite membrane consisting of a
poly(1-butyl-3-vinylimidazolium-tetrafluoroborate) (poly([BVIM]-[BF4])) polymerized ionic liquid graft copolymer (PILGC) and a
blend of PILGC and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]-[BF4]) ionic liquid (IL) to explore techniques for improving the
conductivity of PILGCs, which is normally three orders of magnitude
lower than that of ILs. PILGCs, which are environmentally friendly,
have attracted much interest. To gain a better understanding of ion
transport in composites, the mechanisms of ion transport in composite
components should be explored. We investigated anion transport in
ILs and PILGCs and were able to obtain the correct ion transport mechanisms
in IL-PILGC blends based on a previous work. We performed molecular
dynamics (MD) simulations, which are commonly used to investigate
molecular mechanisms. According to the MD simulation results, in most
IL-PILGC blends of various compositions, the contributions of cations
are greater than those of anions. This is one reason that blends have
higher conductivities than their component PILGCs. To the best of
our knowledge, we are the first to identify ion transport mechanisms
in PILGCs and their blends with ILs by exploring subdiffusive ion
motion regimes. The ratio of the number of cages with more than three
cationic branch chains in the blend with 50 wt % PILGC, the blend
with 80 wt % PILGC, and the PILGC was 0.26:0.39:0.65. Therefore, the
ratio of firm cages gets a promotion as the PILGC content increases.
Because the ratio of fast ions decreases as the ratio of firm cages
increases, the blend with 80 wt % PILGC has lower anion diffusivities
than the blend with 50 wt % PILGC. It was inappropriate to probe ion
transport in PILGCs (or IL-PILGC blends) solely via analyzing ion
association interactions. Analysis of only ion association interactions
led to the incorrect conclusion that the time scales of ion transport
in PILGCs are given by the continuous ion association time, which
is the time when the ion association remains paired rather than the
time when an ion is caught inside a cage. Proper methods should be
used to obtain more accurate theories.