The solution properties of amphiphilic molecules in nonaqueous polar solven
ts are important in the elucidation of the effects of solvent quality on se
lf-assembly and also in practical applications where the use of water as a
solvent is undesirable. We used small-angle neutron scattering (SANS) to in
vestigate the micellization of a poly(ethylene oxide)-poly(propylene oxide)
-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer (Pluronic P105: EO37PO5
8EO37) in formamide as a function of block copolymer concentration tin the
range 1-20 wt %) and temperature (10-60 degrees C). Results on the micelliz
ation thermodynamics and the micelle structure are presented here. PEO-PPO-
PEO block copolymers self-assemble in formamide into micelles upon increasi
ng the temperature, indicating an endothermic micellization. The enthalpy a
nd entropy of micellization in formamide are about 3 times smaller than the
respective quantities in water. The radius of gyration of the unimers and
the core radius and hard-sphere interaction radius of the spherical micelle
s were obtained by fitting appropriate models to the SANS scattering patter
ns. The degree of swelling of the block copolymer micelles by the solvent;
was estimated on the basis of the different radii. The micelle radii and th
e corresponding number of block copolymers that participate in each micelle
increase with increasing temperature. The amount of solvent in the micelle
corona decreased with increasing temperature up to 15 degrees C above the
critical micellization temperature and then remained constant (for the temp
erature range examined) at a value of about 1.5 solvent molecules per ethyl
ene oxide segment.