| Summary: | 碩士 === 國立成功大學 === 化學系碩博士班 === 96 === 1-butyl-3-methylimidazole tetrafluoroborate (BMIBF4) and 1-butyl-
3-methylimidazole tetra-fluoroborate(BMIPF6) was respectively mixed
firstly with various diluents such as polyethyleneglycol(PEG MW=
200、300、400 ) and polyehtyleneimine (PEI MW=423)
Nuclear Magnetic resonance techniques were then applied to
investigate the influences of solvent content(x=0.05、0.1、0.2、0.3、0.4、
0.5)and temperature variations (303-338 K) on the chemical shift,
diffusion coefficient. The physical properties, like viscosity, density and
conductivity of the mixture were also measured to understand further the
dynamics and structure of mixed solutions.
The results showed that intermolecular hydrogen-bonding forms
between the O lone-pair electrons of solvent PEG and the H’s in BMI+
ring. The 1H chemical shift difference is closely related to the distance
between BMI+ and BF4
- or PF6
- ions. It’s also found from the HOESY
spectra that hydrogen bond is also formed between the alkyl hydrogen of
the solvent and the 19F atom of BF4
- and PF6
-. As solvent content
increases, the viscosity and conductivity of solution falls, the movement
of the anions increase and that of the cations decrease thereupon from the
diffudion coefficient measurements.
We found that the Hydrodynamic radius and the Aggregation
became larger and the Transport number of BMI+ became smaller, which
indicate that when the PEG mix with the BMIBF4 、BMIPF6, the PEG
utilizes its lone electron pairs to form hydrogen bond with the H atom of
IV
BMI+ ring and cove BMI+. However, the added PEG just makes the
average distance between BMI+ and F- larger and produces cluster
without dissociating BMI+ and its counter anion by simultaneously
H-bonds with BMI+ and its counter anion. When the molecular weight
and the consistency of PEG are getting larger, the obvious effect of
coving will generate larger clusters involving PEG, BMI+ and its counter
anion. Besides, the BMIBF4/PEG system has an even smaller group of
BF4
- in comparison with PF6
- and is easier to generate clusters than the
BMIPF6/PEG system. No matter which PEG solvent could induce the
shift in aggregation from big cluster for pure ionic liquid to smaller
cluster without dissociation of ion pairs. In addition, since the structure of
PEI is rigid, it does not have a good interaction with BMIPF6, and is
difficult to generate clusters with BMIPF6 via coving.
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