Intermolecular structure in a polymer glass: electronic excitation transfer studies

Abstract

Electronic excitation transport among interacting polymer molecules lightly tagged with chromophore substituents is examined as a function of tagged polymer concentration in the polymeric solid. The technique of time-correlated single photon counting is employed to obtain time-resolved fluorescence depolarization data on solid mixtures of poly(methy1 methacrylate-co-2-vinylnaphthalene) in a poly(methy1 methacrylate) host. The time-dependent fluorescence anisotropy, the energy transport observable, is compared to a theory developed to model this system. The theory is based on a first-order cumulant approximation to the transport master equation. The model makes use of the Flory "ideality" postulate by depicting the intramolecular segmental distribution as a Gaussian with a second moment that scales linearly with chain size. At low copolymer concentration, the dynamics of excitation transfer depend only on intramolecular structure. At high copolymer concentration, excitation transfer occurs among chromophores on different copolymers in addition to intramolecular transfer. The only adjustable parameter in the treatment is the form of the intermolecular radial distribution function, g(r). The sensitivity of the model is analyzed with respect to the behavior of g(r). The theoretical treatment provides a quantitative description of the time and concentration dependence of the excitation transfer for the case of g(r) = 1 when r L 20 A.

Nanodomain formation in a liquid polymer blend: The initial stages of phase separation

“…18 The technique has been applied to experimental studies of concentrated micelle suspensions with chromophores restricted to the micelle surfaces, 17 and to pendant chromophores covalently bound to the backbones of interpenetrating polymer chains. 15 For the micelle system, the accuracy of the method has been confirmed by comparison to the results of Monte Carlo simulations. 16 In both experimental situations, EET occurs within a chromophore cluster, e.g., a micelle or a polymer coil, and between clusters.…”

“…The formulation is similar to one presented in Ref. 15; however, here the effects of molecular aggregation are accounted for in the observables. We adopt a formalism which makes use of a truncated cumulant approximation to the Green's function solution of the Pauli master equation.…”

“…In Ref. 15, the Gaussian chain model was successfully employed to obtain an analytic description of the excitation dynamics of the copolymer in PMMA.…”

“…2,[15][16][17][18][19][20][21][22][23][24][25][26][27] Since the emission of fluo-rescence occurs against a dark background, it is possible to obtain high quality data from very low concentrations of light-emitting probe molecules ͑chromophores͒. Moreover, fluorescence measurements are a straightforward method for the examination of the excited-state dynamics associated with systems of interacting chromophores.…”

Polystyrene Size Determination in Polystyrene and Poly(vinyl methyl ether) Using Electronic Excitation Transport

“…Thus, naphthalene has a high sensitivity to the presence of other chromophores within approximately a 30 Å range, a distance which is well suited to the study of problems of polymer segmental interactions. Theoretical treatments of the excitation-transfer dynamics among chromophores on polymer chains 1,5 make it possible to extract quantitative information regarding the distribution of chain segments. Since the dynamics of excitation transfer are highly sensitive to the chromophore distribution, any change in sample conditions that alters the distribution will be reflected in a change in r(t).…”