  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.
