DES-Modified Magnetic Nanoparticles Modulate the Hydrophilic–Hydrophobic Balance of PACMO-b-PNIPAM in Aqueous Media

A promising approach for developing smart hybrid materials with customizable structures and properties involves deciphering the molecular level interplay between their components. The present study aims to explore the interactions between poly(N-acryloylmorpholine)-b-poly(N-isopropylacrylamide) (PACMO-b-PNIPAM) block copolymer (BCP) and Fe3O4 magnetic nanoparticles (MNPs) modified with deep eutectic solvents (DESs). The modification of MNPs was carried out using three different DESs─monocholinium citrate-ethylene glycol ([Chn][Cit]-[EG]), dicholinium citrate-ethylene glycol ([Chn]2[Cit]-[EG]), and tricholinium citrate-ethylene glycol ([Chn]3[Cit]-[EG]), referred to as DES-1, DES-2, and DES-3, respectively. To carry out the molecular level investigation, different biophysical techniques such as UV–visible, fluorescence spectroscopy, Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), ζ-potential, and transmission electron microscopy (TEM) were employed. The presence of DES-modified MNPs enhances the interaction between the BCP and the surrounding medium. Thermal fluorescence analysis reveals a slight enhancement in the lower critical solution temperature (LCST) of the BCP. The DES-modified MNPs increased the LCST of the BCP by 1.99 °C, 1.64 °C, and 2.15 °C for DES-1, DES-2, and DES-3 modified MNPs, respectively, for 0.1 mg/mL of nanoparticles. This indicates a trend toward the stabilization of the expanded conformation of BCP in the presence of MNPs. Size measurements designate an increase in the hydrodynamic size (dH) of the BCP in MNPs and DES-modified MNPs in a concentration-dependent manner, while TEM images confirm the formation of polymer-NP assemblies with different aggregation characteristics depending on the DES coating. Overall, the modification of MNP with DES substantially reworks their interaction with BCP. This study provides a valuable tactic for fine-tuning the conformation, stability, and thermoresponsive properties of the polymers in aqueous media.