Energy Transfer Study of the Cylindrical Interface Formed by Asymmetric Isoprene−Methyl Methacrylate Diblock Copolymers Bearing a Dye at the Junction

Abstract

The experiments described here were designed to determine the characteristic width δ of the cylindrical interface in a block copolymer that forms a hexagonal phase in the bulk state. We used fluorescence resonance energy transfer (FRET) to study films consisting of mixtures of donor- and acceptor-labeled poly(isoprene-b-methyl methacrylate) (PI−PMMA, 29 vol % PI). Dye labels were attached at the PI−PMMA junctions. Because the dyes are connected to the junctions, they are confined to the block copolymer interface. To obtain information about the width of the interface separating the components, we compared measured and simulated donor fluorescence decay profiles. We developed a Monte Carlo method to introduce donor and acceptor sites within the interface and then used this dye distribution to calculate simulated “experimental” decay profiles. In this way we were able to examine the appropriateness of using a preaveraged value of the orientation parameter in evaluating FRET data. We found that a value of 〈|κ|〉2 = 0.40 gave a reasonable agreement with results obtained by considering random orientation of dipoles for each donor−acceptor pair. Through these experiments, we found a value of δ slightly smaller than 1.0 nm, confirming that PI and PMMA are very meagerly miscible polymers.

Determination of the Förster Distance in Polymer Films by Fluorescence Decay for Donor Dyes with a Nonexponential Decay Profile

“…By chemically attaching donor and acceptor dyes to polymer chains, it is possible to use FRET experiments to measure parameters such as the polymer radius of gyration 1 and diffusion coefficients 2 as well as parameters characteristic of dynamic properties of macromolecules 3 or the interface between two different phases in an immiscible blend 4 or in a block copolymer. 5 There has been a long history of using fluorescence resonance energy transfer in our group for studying polymer melts. These experiments employ donor and acceptor dyes that are covalently bound to polymers as a means of studying aspects of morphology and miscibility between polymeric phases.…”

On Cylindrical PS-b-PMMA in Moderate and Weak Segregation

“…With one exception, the photophysical and related parameters we employed in the fluorescence decay simulations were taken from ref . For both systems, we used an unquenched decay time, τ D , of 43.3 ns, and a preaveraged orientation factor, ⟨|κ|⟩ 2 , of 0.476 .…”

“…Since neither the width nor anisotropy of the junction distributions is known, one cannot now predict how these factors affect the final product. Our overall goal in this paper is to shed light on some of these matters, including the PS- b -PMMA junction distributions, the interface shape and thickness, and how these properties affect fluorescence decay measurements , in fluorescence nonradiative energy transfer (FRET) experiments on junction-labeled samples, a technique that can be used to probe these systems …”

“…The approach extends earlier work in which we employed Monte Carlo simulations to analyze experimental fluorescence decay data in FRET experiments on cylindrical polyisoprene- b -poly(methyl methacrylate) (PI- b -PMMA) samples. That system is strongly segregated, the junction distributions and the interfaces between the blocks are narrow and essentially isotropic, and the interfaces in one cell are well separated from those in neighboring cells.…”

Systematic study of the fluorescence decays of amino‐coumarin dyes in polymer matrices

“…Clearly, this ruler can come in quite handy for studying polymers, as many important structural features in polymeric materials have spatial dimensions on the order of 1–10 nm. By chemically attaching donor and acceptor dyes to polymer chains, it is possible to measure parameters such as the polymer radius of gyration,7 polymer self‐diffusion coefficient,8 the concentration where overlap occurs between different polymer chains,9 and the thickness of the interface between two different phases in an immiscible blend10 or block copolymer 11…”