Phase Separation in Binary and Ternary Polymer Composites Studied with Electronic Excitation Transport

Abstract

Time-resolved fluorescence polarization anisotropy decay measurements are used to observe the process of phase separation of molecularly mixed polymer blends. The binary blends are composed of a low concentration of poly[methyl methacrylate-co-2-vinylnaphthalene] (PMMA2VN) in poly[vinyl acetate] (PVAc). The small number of 2VN groups on the PMMA2VN chains act as fluorescent chromophores. Electronic excitation transport (EET) among these chromophores contributes to the decay of their fluorescence polarization anisotropy, which is measured with time-correlated single photon counting. Since EET is 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 scale. Blend samples are prepared by annealing a homogeneous blend at an elevated temperature for a given time and then rapidly quenching the phase-separating material below its glass-transition temperature. The newly formed nanoscopic aggregates frozen in the sample are then investigated with EET. The ternary blends are composed of a very small amount of PMMA2VN and a larger quantity of PMMA, both in bulk PVAc. In the phase separation of ternary blends, the PMMA2VN component initially partitions with its chromophore-free counterpart, expanding to its θ-condition size before continuing to aggregate and eventually separating from the PMMA.

Energy Migration Study of Random Immobile Anthracene Derivatives by Time-Resolved Fluorescence Anisotropy Decays

“…20,21 Fayer's group has exploited this sensitivity to study changes in polymer chain conformation as well as phase separation in polymer blends. [3][4][5] If the emission depolarization occurs only by energy migration, it can be described by the Fo ¨rster energy transfer mechanism. 20,22,23 In most theoretical treatments of nonradiative energy transfer, the time-dependent anisotropy decay is developed in terms of the survival probability of the initially excited chromophore, Ψ(t).…”

“…It is possible to apply this technique to study a variety of features of polymeric systems at the molecular level. These include studies of polymer chain conformation, phase behavior in polymer blends, − and polymer diffusion in latex films, , as well as the nature of the interface separating the microphase-separated components of block copolymers in bulk − and in micellar solution …”

“…Time-resolved fluorescence anisotropy measurements are an effective technique to measure the time-dependent emission polarization loss. Unlike fluorescence intensity decay, anisotropy decay is very sensitive to the change of the dipole orientation. , Fayer's group has exploited this sensitivity to study changes in polymer chain conformation as well as phase separation in polymer blends. − …”