How Does a Smart Polymer Respond to Imidazolium-Based Ionic Liquids?

Abstract

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.

Tweaking Behavior of Hydrogen Bond Donor in Choline Chloride-Based Deep Eutectic Solvents for Regulating the Phase Transition of Poly(N-vinylcaprolactam): A Sustainable Medium for an Early Hydrophobic Collapse

“…Figure shows the UV–visible spectra of 8-anilinonaphthalene-1-sulfonic acid (ANS) in a PVCL aqueous solution with varying concentrations of ChCl:urea, ChCl:EG, and ChCl:LA. The absorption maximum (λ max ) of ANS in the PVCL aqueous solution shows a characteristic peak at ∼380 nm, which is consistent with that reported in the literature. ,, With the addition of varying concentrations of ChCl:urea, a decrease in absorbance at 380 nm was observed, as shown in Figure (a). With the addition of ChCl:EG (Figure (b)), a very small change in absorbance was observed even at higher concentrations.…”

“…Poly­( N -vinylcaprolactam) (PVCL) has received significant attention due to its characteristic features and diversified applications in biomedical science and pharmaceutical industries. − Owing to its tremendous sensitivity and biocompatibility, PVCL-based “smart” materials such as nanohybrids, microgels, hydrogels, and copolymers have been widely used in various applications. ,− PVCL can respond to different stimulants, such as proteins, temperature, ionic strength, and osmolytes. − Deep eutectic solvents (DESs) are an emerging class of benign liquid formulations that have gained popularity owing to idiosyncratic properties that outperform traditional ionic liquids (ILs). − High solubilization power, solventless preparation, low volatility, good stability, cost effectiveness, and wider availability are some of the properties of DESs that make them an ingenious and perfect solvent alternative. − The DESs consist of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) groups.…”

“…Researchers have successfully tuned the lower critical solution temperature (LCST) of thermoresponsive polymers (TRPs) by simply adding cosolvents in the system and have widely predicted that cosolvents that are partitioned to the polymer surface increase the LCST, whereas cosolvents which depleted from the polymer surface decrease the LCST. − Studies have also been performed to understand the molecular mechanism behind the cononsolvency of the TRPs observed in the presence of a binary mixture of two good solvents such as water and alcohols . Imidazolium-based ILs have shown excellent ability to tune the LCST of PVCL. ,,− In this regard, Umapathi et al studied the efficiency of imidazolium-based ILs on the LCST of PVCL. Wu and co-workers − also extensively studied the transition behavior of the TRPs and successfully tuned the LCST in the presence of ILs.…”

“…25 Imidazolium-based ILs have shown excellent ability to tune the LCST of PVCL. 7,10,20−22 In this regard, Umapathi et al 7 studied the efficiency of imidazoliumbased ILs on the LCST of PVCL. Wu and co-workers 20−23 also extensively studied the transition behavior of the TRPs and successfully tuned the LCST in the presence of ILs.…”

Polymers Exhibiting Lower Critical Solution Temperatures as a Route to Thermoreversible Gelators for Healthcare

“…[ 167 ] Its LCST in water may be increased by the presence of ionic liquids, which are hypothesized to act as a bridge between PNVCL and water, improving solvation. [ 168 ] A draw‐back of this polymer arises due to difficulty experienced when attempting to polymerize the N ‐vinyl caprolactam monomer in a controlled manner. [ 169 ] This is as a consequence of the poor radical stability formed by the monomer during polymerization, leading to N ‐vinylcaprolactam being considered a “less activated monomer”.…”