Neutron spin-echo study of the dynamic behavior of amphiphilic diblock copolymer micelles in aqueous solution

We examined the dynamics of amphiphilic polymer micelles of the diblock cop olymer HOVE-NBVE (hydroxyethylvinyl ether as a hydrophilic segment and n-bu tylvinyl ether as a hydrophobic segment) in aqueous solution using the neut ron spin-echo (NSE) technique. The time-correlation function obtained for t he polymer micelles was well fitted by double exponential function, and the fast and slow modes could be estimated separately. The slow mode was domin ant at smaller scattering angles, and showed an excellent linearity in Gamm a (decay rate) vs q(2) (scattering vector) plot. The diffusion coefficient evaluated from its slope and the hydrodynamic radius, R-h, by the Einstein- Stoke equation were consistent with the size of the polymer micelle that wa s estimated by small-angle neutron scattering (SANS), small-angle X-ray sca ttering (SAXS), and dynamic light scattering (DLS). Hence, this slow mode r eflects the translational diffusion of the polymer micelle in aqueous solut ion. The fast mode, which was 1 order of magnitude faster than the slow mod e, was a major factor for larger scattering angle regions in which the SANS curve showed blob scattering Thus, the fast mode appears to be an internal motion of the polymer micelle, like the breathing mode of the hydrophilic shell (corona) around the polymer micelle.