DWS-based microrheology of triblock copolymers

TL;DR

This study employs DWS-based microrheology to investigate phase transitions and viscoelastic properties of Pluronic F127 solutions across a temperature range, revealing insights into high-temperature behavior and phase changes.

Contribution

It demonstrates the effectiveness of DWS microrheology in studying phase transitions and viscoelastic properties of triblock copolymer solutions at high temperatures, which are challenging for classical methods.

Findings

DWS microrheology can measure effective viscosities and critical micellization points.

High EO/PO ratio influences high-temperature re-entrant liquid phase.

Microscopic viscoelastic moduli reveal phase transitions and solid-phase properties.

Abstract

The thermally reversible phase transitions in aqueous solutions of the triblock copolymers known as Pluronic and their related textures are well-researched. However, their corresponding rheological properties are less studied. In particular, their high-temperature behavior is difficult to access with classical rheology. Here we demonstrated that Diffusing Wave Spectroscopy (DWS)-based microrheology allows us to study the phase transition and the associated viscoelastic properties of Pluronic F127 solutions for temperatures from 5 C to 80 C. From the measured intensity-autocorrelation functions we can extract effective viscosities and determine the critical micellization temperature and concentration. Moreover,the high EO/PO (arm-to-core) ratio of F127 and its polydispersity play a critical role in the high-temperature re-entrant liquid phase, due to decreasing solubility of PEO along with the dehydration of the PPO core. The microscopic viscoelastic moduli G'({\omega}) and G''({\omega}) help to determine these phase transitions and provide mechanical properties in the solid phase that are not readily accessible with standard multi-particle tracking techniques due to limited Brownian motion.