Small-Angle Neutron Scattering study of solubilization of tributyl phosphate in aqueous solutions of L64 Pluronic triblock copolymers

TL;DR

This study investigates how tributylphosphate solubilizes in aqueous L64 Pluronic solutions, revealing complex phase behavior, microstructure changes, and surfactant conformational shifts using light scattering and SANS techniques.

Contribution

It provides detailed insights into the microstructural evolution and surfactant conformational changes during TBP solubilization in Pluronic solutions, combining multiple scattering methods.

Findings

Identification of phase transitions at different oil contents and temperatures.

Observation of microemulsion droplet size and structure changes.

Detection of surfactant conformational shifts linked to morphological evolution.

Abstract

We have studied the solubilization behaviour of tributylphosphate (TBP) in aqueous solutions of L64-Pluronics, using light and small angle neutron scattering (SANS). Varying the temperature and the oil-content, the system presents a non trivial phase behaviour. In particular, at 308K, a first solubilization followed by an emulsification failure and a resolubilization is found. We have measured the microstructure by SANS and characterized the microemulsion droplet core-size, corona-thickness, polydispersity, and interactions. It is shown that at low oil content, the system is made of small swollen micelles. After the phase separation, the resolubilization is carried by larger oil droplets decorated by copolymer. From specific surface measurements at large angles, a surprising change in surfactant conformation is found to accompany this morphological evolution which is also supported by previous results obtained from 1H NMR experiments. In independent measurements, our structural modelling is confirmed using contrast-variation SANS.