Rheological signatures of gel–glass transition and a revised phase diagram of an aqueous triblock copolymer solution of Pluronic F127

Abstract

In this work, we study temperature-induced state change of an aqueous solution of triblock copolymer composed of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO (Pluronic F127), at different concentrations using rheology. While this temperature-dependent state change visually appears like a liquid–soft solid transition, and the soft solid state has been termed as a gel in the literature, there is a debate regarding the precise microstructure of the soft solid state. We observe that over a concentration domain of interest, an aqueous solution of F127 overwhelmingly demonstrates all the characteristic rheological features of not just a sol–gel–glass transition at low temperatures and glass–liquid transition at high temperatures, but also that associated with the individual states, such as sol, post-gel, and glass. The temperature at which the gel–glass transition is observed decreases while the temperature associated with glass–liquid transition increases with an increase in the concentration of F127. Based on the observed behavior, we propose a mechanism that considers the change in micelle volume fraction and alteration of the hydrophilicity of PEO corona as a function of temperature. Finally, we construct a phase diagram and discuss the similarities and differences with respect to various phase diagrams of F127 solution available in the literature.

Preparation, Structural Characterization of Anti-Cancer Drugs-Mediated Self-Assembly from the Pluronic Copolymers through Synchrotron SAXS Investigation

“…This may facilitate the expulsion of 5-FU from the lamellar microstructure. Phase transition from lamellar to hexagonal was not observed in our case [ 18 ], however, the identified phase is in good agreement with the phase diagram [ 28 ].…”

Emergent hybrid mesophases in ternary mixtures of cellulose nanocrystals ‐ Pluronic micelles‐water

“…At first glance this peak could be mistaken for the shoulder of a second‐order interference peak seen in the SAXS patterns of CNCs suspensions, however, the failed attempts to reconstruct the scattering patterns of these mixtures by superposition of the scattering curves of the individual components (Figure S5) indicate that this is not the case. As the F127 concentration is well above the CMC, with a typical micelles diameter of ~20 nm ±5 (Table 1), 63 it is likely that the peak is a result of scattering from “free” F127 micelles. Thus, we reconstructed the SAXS patterns of the liquid mixtures comprising 7 wt% CNCs + X wt% F127 by the superposition of the scattering curves of 7 wt% CNCs + 10 wt% F127 with the scattering curves obtained from (X‐10) wt% F127 (Figure S5).…”

Effect of thermal and mechanical rejuvenation on the rheological behavior of chocolate

“…However, the decrease in magnitude of slope subsequent to mechanical rejuvenation is more gradual and does not lead to saturation as observed for the thermally rejuvenated system over the explored time domain. As discussed before, the presence of a negative slope suggests network like structure and a decrease in its magnitude indicates an enhancement in the network density 26,70,71 . Clearly, this dynamics is more gradual subsequent to mechanical rejuvenation than that of after thermal rejuvenation.…”

“…dominance. Such behavior is reminiscent of a network structure 26,70,71 . With increase in 𝑡 𝑤 , the magnitude of slope of 𝐻(𝜏) versus 𝜏 decreases and the curves becomes progressively flat.…”