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

초록

Deep eutectic solvents (DESs) are recognized as a "green" alternative to conventional ionic liquids and organic solvents owing to their specific properties. In this study, the influence of DESs containing choline chloride (ChCl) as a hydrogen bond acceptor (HBA) and urea, ethylene glycol (EG), and lactic acid (LA) as hydrogen bond donors (HBD) on the thermoresponsive behavior of poly(N-vinylcaprolactam) (PVCL) is investigated using various techniques. Spectroscopic investigations indicate biased interactions of the HBD group present in the DESs with a hydration layer of PVCL. Dynamic light scattering and temperature-dependent fluorescence spectroscopy results clearly show a decrease in the lower critical solution temperature of PVCL in the presence of the DESs. The hydrophobic collapse of PVCL in the presence of the DESs follows the order ChCl:urea > ChCl:EG > ChCl:LA. It is proposed that the presence of DESs does not interfere with the functional groups present in PVCL; however, it ruptures the hydrogen bonding between PVCL and the water molecules and destabilizes the water gradient around PVCL. The DESs have provided an alternative platform for low-temperature dehydration of PVCL, which can be useful as a drug carrier agent.

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