Gaussian- to stretched-coil transition in block copolymer melts.

Abstract

Two scaling regimes, D\ensuremath{\sim}${\mathit{N}}^{\mathrm{\ensuremath{\delta}}}$ with \ensuremath{\delta}=0.49\ifmmode\pm\else\textpm\fi{}0.02 and 0.80\ifmmode\pm\else\textpm\fi{}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 \ensuremath{\delta}=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), ${\mathit{N}}_{\mathrm{GST}}$=0.57${\mathit{N}}_{\mathrm{ODT}}$. We associate \ensuremath{\delta}=0.80 with the crossover from weak-segregation (\ensuremath{\delta}=1/2) to strong-segregation (\ensuremath{\delta}=2/3) behavior.