Thermal transitions in associating aqueous block copolymers: light scattering, rheology and spectroscopy

Abstract

Solutions containing a polyoxy-ethylene/polyoxy-propylene/polyoxy-ethylene (PEO-PPO-PEO) block copolymer, indicated as F68, in water were investigated as a function of composition and temperature. Hydrogen nuclear magnetic resonance (H-1 NMR) line width, chemical shift, self-diffusion, spin-lattice relaxation times, laser light scattering and rheological methods were used. The monomer-micelle equilibrium and the micelle-liquid crystalline phase transitions depend on the F68 content in the mixture and temperature. Significant changes in light scattering intensity and apparent hydrodynamic radius are associated to micelle formation above the critical micellar temperature (CMT). According to a Contin analysis, this behaviour is reflected in the presence of two populations in the intensity-intensity autocorrelation functions. The contributions due to molecules and micelles can be evaluated separately. No such effects are observed below the CMT. Micelle onset is also associated to variations in H-1 NMR spectra, affecting the chemical shift, line width and spin-lattice relaxation time of the PPO methyl protons and self-diffusion, as well. Spin-lattice relaxation times of PEO chains, conversely, change significantly at temperatures close to the micelle-liquid crystalline thermal transition. Similar results were obtained from the line width of H-2 NMR spectra as a function of T. Significant changes in both viscous and elastic modulus were also observed and ascribed to PPO dehydration, at the CMT, as well as to squeezing and dehydration of PEO units in liquid crystal formation, respectively

Electrostatic Interactions between a Protein and Oppositely Charged Micelles

“…An argon ion laser, operating at 514.5 nm and 20 mW, was used. Details on the apparatus, measuring procedures, and data elaboration are given elsewhere. − The Malvern HT-ZS Nano unit performed DLS measurements in backscattering mode, at 632.8 nm, 173°, and 25.0 ± 0.1 °C. The agreement between particle sizes inferred by the two methods is within a few percent.…”

Role of hydration and water coordination in micellization of Pluronic block copolymers

“…Polymer-water interactions and water structure play an important role in kinetics and mechanism of loading of therapeutics and their release in hydrogels [4,5]; mechanical properties of a polymer may change if a small amount of water is adsorbed to it [6]. These interactions may significantly depend on temperature and concentration [7].…”

Temperature and concentration effects on supramolecular aggregation and phase behavior for poly(propylene oxide)–b-poly(ethylene oxide)–b-poly(propylene oxide) copolymers of different concentration in aqueous mixtures, 2

“…Sol-gel transition concentration, as well as critical micelle concentration (c.m.c.) and thermodynamical quantities of the micellization processes have also been investigated as a function of the temperature [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. Generally at low concentration Pluronic molecules exist in solution as individual unimers.…”