The structure of P85 Pluronic block copolymer micelles determined by small-angle neutron scattering

The symmetric triblock copolymer Pluronic P85 with EO25PO40EO25 has been studied by small-angle neutron scattering (SANS) at 50 and 60 °C at concentrations of 0.25–10 wt.% in D2O. The data are analyzed by a model based on Monte Carlo simulations. The micelles are modeled as having a spherical core of poly(propylene oxide) (PPO) with some water surrounded by a corona of the poly(ethylene oxide) (PEO) block. The latter are non-interacting and obey Gaussian statistics, but are expelled from the core region. The analysis shows that the micelles are fairly concentration and temperature independent at the conditions studied. The micelles are slightly polydisperse in the aggregation number and have aggregation numbers in the range 40–50. The core contains about 40% water and has a radius of about 40 Å. The corona extends out to about 80–100 Å and has a fairly low volume fraction of polymer, typically less than 10%.