Asymmetric diblock copolymers - Phase behaviour and kinetics of structure formation

The structure of a series of three molecular weights of diblock copolymers polystyrene/b-isoprene with 11% volume fraction of polystyrene and low polydispersity has been investigated using small angle X-ray scattering (SAXS). In between the disordered and the BCC ordered state a micellar state with liquid-like order was found. The transition between these states was investigated in a temperature-driven experiment. Whereas the micelles appear gradually with lowering temperature the formation of the BCC ordered state occurs discontinuously at a well-defined temperature. Detailed analysis of the scattering profiles provides access to the micellar size and distance in the liquid-like as well as in the BCC state. The kinetics of the ordering transition was studied using time-resolved SAXS after temperature jumps from the liquid-like to the BCC state. The growth of the micelles and their ordering on the periodic lattice were found to occur on clearly separated time scales.