Gaussian- to stretched-coil transition in block copolymer melts

Two scaling regimes, D{~}N^δ with {δ}=0.49±{}0.02 and 0.80±{}0.04, have been identified in a model set of nearly symmetric diblock copolymer melts, where D and N are the system peridocity and degree of polymerization, respectively. The crossover from {δ}=0.49 to 0.80 is identified as the Gaussian to stretched-coil transition (GST). Contrary to current theory, the GST occurs well below the order-disorder transition (ODT), NGST=0.57NODT. We associate {δ}=0.80 with the crossover from weak-segregation ({δ}=1/2) to strong-segregation ({δ}=2/3) behavior.