Chain exchange kinetics of diblock copolymer micelles studied by nonradiative energy transfer. 1. Experimental design and theory

Liu, Guojun

doi:10.1139/v95-246

Cited by 10 publications

(3 citation statements)

References 26 publications

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“…We then assume, as was done in a previous paper by one of us on the design of experiments for micelle chain exchange kinetic studies, that the experiment is performed using a higher molar micelle concentration of polymer I than the molar polymer concentration of polymer II. This makes the probability for finding micelles, at the end of the experiment, containing more than one polymer II chain negligible and leads to a great simplification of our later mathematical derivation for an expression for I Py ( t ).…”

Section: Discussion Of the Experiments And Theorymentioning

confidence: 99%

Determination of the Rate Constant for Chain Insertion into Poly(methyl methacrylate)-block-poly(methacrylic acid) Micelles by a Fluorescence Method

and

Liu

1996

Macromolecules

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Poly(methyl methacrylate)-block-poly(methacrylic acid) (PMMA-b-PMAA) with and without pyrene labels attached to the end of the PMAA block have been synthesized and characterized. These polymers formed micelles with PMAA as the core in ethyl acetate/methanol mixtures when the ethyl acetate volume fraction was higher than 80%. After mixing a micelle solution of PMMA-b-PMAA without pyrene labels, i.e., polymer I, with a unimer solution of the sample with pyrene, i.e., polymer II, the fluorescence intensity IPy(t) of pyrene increased with time. This was caused by the insertion of the pyrene group of polymer II chains into the rigid core of polymer I micelles. The pyrene fluorescence quantum yield is higher in a more rigid environment due to the reduced quenching of pyrene fluorescence by oxygen and the possible suppression of certain nonradiative deactivation pathways. A kinetic model has been proposed for describing the chain insertion process. Fitting the experimental fluorescence intensity data using the derived expression for IPy(t) allowed the first determination of the rate constant kn for diblock copolymer chain insertion into micelles.

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Section: Discussion Of the Experiments And Theorymentioning

confidence: 99%

Determination of the Rate Constant for Chain Insertion into Poly(methyl methacrylate)-block-poly(methacrylic acid) Micelles by a Fluorescence Method

and

Liu

1996

Macromolecules

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“…Both factors contribute to the high activation barrier for the chain expulsion from the micelle and add to the difficulty of the experiments. Chain exchange kinetics between micelles have been studied using T-jump light scattering, − nonradiative energy transfer spectroscopy and fluorescence quenching spectroscopy, − and transmission electron microscopy; − however, a general, quantitative picture has not emerged. Richter and co-workers − used small-angle neutron scattering (SANS) to investigate chain exchange for poly(ethylene oxide)- block -poly(ethylene- alt -propylene) (PEO- b -PEP) in water/ N , N -dimethylformamide (DMF) mixtures and later reported a quasi-logarithmic time dependence for the overall chain exchange rate. − Lodge, Bates, and co-workers systematically studied chain exchange of a series of poly(ethylene- alt -propylene)- block -poly(styrene) (PEP- b -PS) diblocks in squalane and elucidated the effect of N core , and its dispersity ( Đ ), temperature, − concentration,and polymer architecture (using PS- b -PEP- b -PS and PEP- b -PS- b -PEP) on the micelle chain exchange kinetics.…”

Section: Introductionmentioning

confidence: 99%

Chain Exchange Kinetics in Diblock Copolymer Micelles in Ionic Liquids: The Role of χ

Lodge

2016

Macromolecules

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Chain exchange kinetics of diblock copolymer micelles with lower critical micellization temperature (LCMT) phase behavior were investigated using time-resolved small-angle neutron scattering (TR-SANS). Three nearly identical isotopically substituted pairs of poly(methyl methacrylate)-block-poly(n-butyl methacrylate) (PMMA-b-PnBMA) diblocks were used in mixtures of the room temperature ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. In this case, the h-PnBMA and d 9-PnBMA blocks form the micellar cores. The results are consistent with previous measurements in other systems, in that the barrier to chain extraction scales linearly with the core block length. By varying the ratio of the two homologous solvents in the mixture, the value of χ between the core block and the solvent is varied systematically. The results show that the solvent selectivity has a remarkable effect on the chain exchange rate, as anticipated by a previous theory. However, in contrast to an assumption in previous studies, we find that the barrier to chain exchange is not simply proportional to χ. Accordingly, we propose a more elaborate function of χ for the energy barrier, which is rationalized by a calculation in the spirit of Flory–Huggins theory. This modification can account for the chain exchange behavior when χ is relatively modest, i.e., in the vicinity of the critical micelle temperature.

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“…The aggregation behavior of dispersions of diblock copolymers is more complicated than that of low molecular weight surfactants. Many attempts have been made to understand the kinetics and mechanisms of chain exchange between diblock copolymer micelles using a wide range of experimental techniques such as fluorescence nonradiative energy transfer, − temperature-jump measurements, , time-resolved light scattering, , and pulsed-field gradient NMR . These studies mostly focused on marginal amphiphilic systems displaying fast micelle dynamics (e.g., the Pluronics 8 ).…”

Section: Introductionmentioning

confidence: 99%

Consequences of Nonergodicity in Aqueous Binary PEO−PB Micellar Dispersions

2004

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Aqueous micellar dispersions of poly(ethylene oxide)-poly(butadiene) (PEO-PB) diblock copolymers were investigated using cryogenic transmission electron microscopy (cryo-TEM). A variety of binary blends were prepared by premixing (before dispersion) and postmixing (after dispersion) diblocks with varying composition and molecular weight. Cryo-TEM results establish there is no perceptible exchange of macromolecules between aggregates resulting in a nonergodic state, where overall equilibrium is never achieved. However, analysis of many microscopic images leads to the conclusion that these nonergodic micelles relax to a state of local equilibrium through the redistribution of block copolymers within the topological framework established during dispersion. Different average compositions and molecular weights exhibit varying degrees of structural complexity, which appears to peak in the vicinity of network formation. Away from this condition the micelle morphology is relatively insensitive to core or corona polydispersity. However, at compositions where the monomodal and nearly monodisperse amphiphiles produce branched wormlike micelles and a network, bimodal mixtures displayed intramicellar segregation leading to cylindrical undulations and octopus-like aggregates with cylindrical micelles emanating from a single bilayer core. These findings are discussed in the context of interfacial curvature and surfactancy.

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Chain exchange kinetics of diblock copolymer micelles studied by nonradiative energy transfer. 1. Experimental design and theory

Cited by 10 publications

References 26 publications

Determination of the Rate Constant for Chain Insertion into Poly(methyl methacrylate)-block-poly(methacrylic acid) Micelles by a Fluorescence Method

Determination of the Rate Constant for Chain Insertion into Poly(methyl methacrylate)-block-poly(methacrylic acid) Micelles by a Fluorescence Method

Chain Exchange Kinetics in Diblock Copolymer Micelles in Ionic Liquids: The Role of χ

Consequences of Nonergodicity in Aqueous Binary PEO−PB Micellar Dispersions

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