A novel experimental approach involving fluorescence nonradiative energy transfer (NRET) is employed to study the Fickian diffusion of small molecules in rubbery polymer films near the glass transition. A theoretical formalism has been developed which directly relates the small molecule translational diffusion coefficient, 𝒟, to changes in the energy transfer efficiency, E. Values of 𝒟 as low as 5 × 10-16 cm/s have been measured. In this approach, two thin polymer films are sandwiched together, one labeled with either NRET donor or acceptor chromophores and the second doped with the complementary chromophore. Upon annealing for a time t, dopant chromophore diffusion occurs in which E is proportional to (𝒟t)1/2/w, where w is the donor film thickness. Values of 𝒟 for pyrene, N-(2-hydroxyethyl)-N-ethyl-4-(tricyanovinyl)aniline (TC1), bis(phenylethynylanthracene) (BPEA), and decacyclene in poly(isobutyl methacrylate) (PiBMA) and for BPEA in poly(ethyl methacrylate) (PEMA) have been measured over temperatures ranging from ca. T g to T g + 20 °C. Among these chromophores, significant differences in both the magnitude and temperature dependence of 𝒟 were observed and are attributed to differences in molecule size, shape, and flexibility. Two anomalous effects are observed from a comparison of translational diffusion and rotational reorientation dynamics of TC1 in PiBMA near T g. The first is an apparent enhancement in translational diffusion relative to rotational reorientation dynamics, with the average translational displacement of a chromophore during an average rotational relaxation time, 〈τrot〉, being a couple orders of magnitude larger than the length of the molecule. This behavior may be explained by significant local-scale heterogeneity in the polymer, i.e., the broad distribution of polymer α-relaxation times. The second regards the different temperature dependencies of 〈τrot〉 and 𝒟 near T g. This may be explained qualitatively by a strong temperature dependence of the breadth of the distribution of α-relaxation times, an effect known to be present in the TC1−PiBMA system employed in this comparison as well as a variety of other polymer systems near T g.

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A novel experimental approach involving fluorescence nonradiative energy transfer (NRET) is employed to study the Fickian diffusion of small molecules in rubbery poly(isobutyl methacrylate) (PiBMA) films near the glass transition, using a formalism that directly relates the small molecule translational diffusion coefficient, D, to changes in the normalized nonradiative energy transfer efficiency, EN. Values of D for pyrene, 1,3‐bis‐(1‐pyrene) propane (BPP), 1,3‐bis‐(1‐pyrene) decane (BPD), 9,10‐bis‐phenyl ethynyl anthracene (BPEA), diphenyl Disperse Red 4 (DPDR4), and decacyclene in PiBMA are measured over temperatures ranging from approximately Tg to Tg + 25°C. Among these chromophores, significant differences in both the magnitude and temperature dependence of D are observed which are attributed to differences in molecule shape and flexibility, as well as molar volume. Other factors being equal, chromophore flexibility was shown both to increase the magnitude of D and to decrease its dependence on temperature, as does an increase in aspect ratio. For BPD, these effects are attributed to the ability of the flexible molecule to diffuse in a piecewise manner, requiring the cooperative mobility of fewer polymer chain segments than a rigid molecule of the same molar volume. For BPEA and DPDR4, this deviation from D being dominated by molar volume effects is attributed the to high aspect ratio of these elongated molecules. © 1996 John Wiley & Sons, Inc.

XPS when used in conjunction with silylation can determine surface hydroxide. The penetration depth was studied using DRIFT and various silylation conditions. Application of this technique to many different inorganic matrices, including Si,N, , glass, silica thin film, zinc silicate lamp phosphor and AI,O,, is illustrated.

SYNOPSISA novel experimental approach involving fluorescence nonradiative energy transfer (NRET) is employed to study the Fickian diffusion of small molecules in rubbery poly(isobuty1 methacrylate) (PiBMA) films near the glass transition, using a formalism that directly relates the small molecule translational diffusion coefficient, a, to changes in the normalized nonradiative energy transfer efficiency, EN. Values of for pyrene, 1,3-bis-( 1-pyrene) propane (BPP), 1,3-bis-(l-pyrene) decane (BPD), 9,10-bis-phenyl ethynyl anthracene (BPEA), diphenyl Disperse Red 4 (DPDR4), and decacyclene in PiBMA are measured over temperatures ranging from approximately Tg to Tg + 25°C. Among these chromophores, significant differences in both the magnitude and temperature dependence of 23 are observed which are attributed to differences in molecule shape and flexibility, as well as molar volume. Other factors being equal, chromophore flexibility was shown both to increase the magnitude of and to decrease its dependence on temperature, as does an increase in aspect ratio. For BPD, these effects are attributed to the ability of the flexible molecule to diffuse in a piecewise manner, requiring the cooperative mobility of fewer polymer chain segments than a rigid molecule of the same molar volume. For BPEA and DPDR4, this deviation from 33 being dominated by molar volume effects is attributed the to high aspect ratio of these elongated molecules. 0 1996 John Wiley & Sons, Inc. Keywords: small molecule diffusion fluorescence nonradiative energy transfer glass transition temperature rubbery polymer probe shape effects probe flexibility effects