In this research
article, we have explored the changes in the lower
critical solution temperature (LCST) of the poly(N-vinylcaprolactam) (PVCL) in the presence of imidazolium-based ionic
liquids (ILs) with fixed cation 1-butyl-3-methylimidazolium cation
[Bmim+], and commonly used anions such as SCN–, I–, Br–, Cl–, CH3COO–, and HSO4
–. The series of anions also reflect the Hofmeister series of ILs.
The results reveal that the LCST of the PVCL increases with increasing
IL concentration. Interestingly, the results are the reverse of the
PNIPAM with the same ILs where the LCST of PNIPAM decreases linearly
with increase in the IL concentration following the Hofmeister series.
Herein, we observed that the increase in the LCST of PVCL follows
the order of ILs as, HSO4
– < CH3COO– < Cl– < Br– < I– < SCN–. This is the reverse order for Hofmeister series anions effect on
the polymer. Furthermore, the different kind of interactions occur
between ILs and PVCL observed using UV-absorbance, fluorescence, and
FTIR spectroscopy. The predicted mechanism suggest that the ILs act
as bridge between water and PVCL, because the solvation of the polymers
is increased leading to increase in the LCST of the polymer. Moreover,
DLS and FESEM techniques were employed to examine the morphological
changes in the PVCL at different temperature in the presence of various
concentrations of the ILs.
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