Revisiting the salt-triggered self-assembly in very hydrophilic triblock copolymer Pluronic® F88 using multitechnique approach

Abstract

An insight scrutiny into the micellization behavior of a linear triblock copolymer Pluronic® F88 in aqueous potassium chloride (KCl) solutions is put forth through various physicochemical techniques, viz. cloud point, tensiometric, microcalorimetry, fluorescence life-time decay, spectral, and scattering. Phase transitions of 5% w/v F88 in KCl electrolyte environment demonstrated the dehydration of copolymer coil; a decrease in the micellization temperature with increase in [KCl] due to salting out effect was configured with high sensitivity differential scanning calorimetry (HSDSC) and fluorescence spectroscopy conduct. Salting out effect exhibited by PEO and PPO blocks of F88 in the presence of KCl was measured by the variations in the bond stretching, intensity of vibrations, and change in chemical shifts using spectral (Fourier-transfer infrared (FT-IR) and 1H-nuclear magnetic resonance (1H-NMR) spectroscopy) techniques. The micellization that followed the double-relaxation process is further validated, employing ultrasonic absorption spectroscopy. The plausible unimers to spherical micelles transition induced by KCl are confirmed with the measured hydrodynamic diameter (Dh) of micelles using dynamic light scattering (DLS). Furthermore, UV-vis spectroscopy findings depicted the successive solubilization of water-insoluble organic dye (orange-OT) in the examined micellar solution which revealed the salient role of salt-water interaction in emboldening the micellization of F88.