Phase separation in binary and ternary polymer composites studied with electronic excitation transport

Time-resolved fluorescence polarization anisotropy decay measurements are u sed to observe the process of phase separation of molecularly mixed polymer blends. The binary blends are composed of a low concentration of poly[meth yl methacrylate-co-2-vinylnaphthalene] (PMMA2VN) in poly[vinyl acetate] (PV Ac). The small number of 2VN groups on the PMMA2VN chains act as fluorescen t chromophores. Electronic excitation transport (EET) among these chromopho res contributes to the decay of their fluorescence polarization anisotropy, which is measured with time-correlated single photon counting. Since EET i s highly sensitive to the distances between chromophores, it reflects their spatial distribution and can reveal both the isolated-chain structure and the aggregation of polymer chains in the blend on the nanometer distance sc ale. Blend samples are prepared by annealing a homogeneous blend at an elev ated temperature for a given time and then rapidly quenching the phase-sepa rating material below its glass-transition temperature. The newly formed na noscopic aggregates frozen in the sample are then investigated with EET. Th e ternary blends are composed of a very small amount of PMMA2VN and a large r quantity of PMMA, both in bulk PVAc. In the phase separation of ternary b lends, the PMMA2VN component initially partitions with its chromophore-free counterpart, expanding to its theta-condition size before continuing to ag gregate and eventually separating from the PMMA.