EVOLUTION OF BLOCK-COPOLYMER MICELLAR SIZE AND STRUCTURE EVIDENCED WITH CRYO ELECTRON-MICROSCOPY

The equilibration of spherical micelles formed by polystyrene-poly(2-v inylpyridine) (PSPVP) diblock copolymers in toluene is studied by mean s of cryo electron microscopy. The evolution of the micelles in order to reach the equilibrium state involves the transformation of their st ructure and size and requires a considerable time. The micellar size d istribution, which is relatively narrow after dissolution, becomes bro ader with time. The micellar structure changes with time toward a sphe rical form with narrow interfacial zone between the core and corona re gions. The possible scenario of the equilibration process is discussed . The influence of the dilution on the micelles' evolution toward the equilibrium is investigated. It is found that strong dilution can lead to a decrease of the final size of the micelles. The reasons for this phenomenon are discussed.