Time-resolved fluorescence studies of the chain dynamics of naphthalene-labeled polystyrene-block-poly(methacrylic acid) micelles in aqueous media (original) (raw)
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Macromolecules, 1991
A-B-A block copolymers (A = poly(methacry1ic acid), B = polystyrene) have been prepared by anionic polymerization. These amphiphilic copolymers can form stable micelles in water/l,l-dioxane mixtures as well as in water or an aqueous buffer. These micelles are presumed to have a polystyrene core and poly(methacry1ic acid) shell. The ability of the micelles to solubilize and release hydrophobic species was studied by fluorescence methods, primarily using pyrene as a fluorescence probe. The following processes were studied: (1) the effect of pyrene loading on monomer/excimer fluorescence ratio and quenching by Cu2+; (2) the rate of exchange between micelles containing pyrene and other aromatic species by the time dependence of either their monomer/excimer ratio or sensitized fluorescence after mixing micelles; (3) the time dependence of the fluorescence quenching of pyrene following the addition of small molecules (Nfl-dimethylaniline, CC4). The following conclusions were obtained (1) a significant fraction (ca. 20-30%) of the pyrene molecules were on or near the polystyrene-water interface (this depends on loading); (2) diffusion of the probe out of the micelle is the rate-determining step in the release and exchange of large hydrophobes. This process is very slow in ita later phases and probably represents slow diffusion from the core of the polystyrene region of the micelle.
Time-resolved fluorescence study of micellizing block copolymers
Journal of Molecular Structure, 1990
ABSTRACT We have studied the dynamics of polystyrene-block-hydrogenated polyisoprene samples, fluorescently labelled on the polystyrene block, by steady-state and time-resolved fluorometry. In selective precipitants for the labelled block, fluorescent probes are trapped and immobilized in compact micellar cores. The rotation of pendant fluorophors is frozen. However, the fast torsional vibrations depolarize partially the fluorescence. As the rotation of micelles is slow as compared with the fluorescence life-time, a significant residual anisotropy is observed. In good solvents for both blocks, fluorescent probes in expanded copolymer coils are exposed to solvent molecules and free to rotate.
Fluorescence quenching mechanisms in micelles: the effect of high quencher concentration
Journal of Photochemistry and Photobiology A: Chemistry, 2000
In this investigation the fluorescence quenching of fluorescent probe molecules situated within surfactant micelles was examined. The hydrophobic polyaromatic hydrocarbon benzo(a)pyrene (B(a)P) and the more polar 6-propionyl-2-(dimethylamino)-naphthalene (PRO-DAN) were used to assess the effect of high quencher concentration on the quenching process in micelles. Using the surfactant systems sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100), three distinct modalities of quenching were observed. For the TX-100 system, both I − and H 2 O 2 quenching of probe fluorescence reached saturation in efficiency. These data are modeled quite well by assuming a limited number of quenching sites per micelle in conjunction with standard Stern-Volmer quenching dynamics. For the SDS system, similar quenching saturation effects are observed, but the saturation model worked less well. It is suggested that a bimodal distribution of micelle sizes could be responsible. The B(a)P/SDS/I − system is singular in that the quenching does not saturate. The efficiency of quenching here varies approximately with the third power of I − concentration. A resonance energy transfer mechanism is proposed in which B(a)P is quenched by I 3 − .
Langmuir, 1996
Static and dynamic aspects of the partitioning of naphthalene into the hydrocarbon phase in aqueous sodium dodecyl sulfate micelles have been critically examined by nanosecond time-resolved pulse fluorometry. It is shown that, in such a system, a properly detailed analysis of the excited-state decay behavior as a function of progressive partitioning of the solute into increasing concentrations of micelles is capable of revealing and directly quantitating the underlying kinetics of the reversible transfer of naphthalene in its excited state between aqueous and micellar phases. The time-resolved data indicate that, in the aqueous sodium dodecyl sulfate system, the partition coefficient for excited-state naphthalene can differ only marginally from that for the ground state. From the estimate obtained for the rate coefficient for entry of excited-state naphthalene into micelles, it would appear that any barrier to the crossing of excited naphthalene into the micelle, given that a collision has taken place, is likely to be rather small. The contrasting time-resolved behavior of a system in which the basis lifetime of the fluorescence probe in the micellar environment is shorter than that in the bulk environment rather than longer, as in the case examined experimentally, is also modeled. The effects of quenching of the fluorescence at the interface between the micellar and aqueous phases are also examined and discussed in the context of the aqueous cetyltrimethylammonium bromide system.
Fluorescence studies on the characterization of mixed micelles
Journal of Molecular Liquids, 1990
ABSTRACT The characterization and study of the polarity of mixed micelles of sodium decyl and sodium dodecyl sulfate and sodium cholate by fluorescence probing have been carded out. Pyrene and Pyrene-l-carboxaldehyde were used. The obtained results allow the discussion of the changes of micelle structure with composition.
The intramicellar fluorescence quenching in cylindrical micelles. II
Chemical Physics, 1989
A theoretical model developed for the intramicellar fluorescence quenching rate constant in cylindrical micelles is used to simulate the fluorescence decay of a probe solubilized in the presence of a solubilized quencher. Different analytical approximations to the simulated fluorescence decay are evaluated for a range of aggregation numbers, diffusion coefficients and quencher concentrations.
Fluorescence probing of block copolymeric micelles using Coumarin 153
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009
Coumarin 153 (C-153) was used as a fluorescent probe molecule to monitor the possible micellization of several amphiphilic block copolymers, all of which consist of poly(DMA) (DMA = 2-(dimethylamino)ethyl methacrylate) as the hydrophilic block but otherwise differ in the nature of the hydrophobic block, composition and overall morphology. In case of linear triblock poly(DMA-b-MMA-b-DMA) copolymers (MMA = methyl methacrylate), the fluorescence response of C-153 indicates the formation of micelles at [polymer] ∼0.03%. The probe molecules are preferentially accommodated in the hydrophobic core region of these nano-sized micelles, which is characterized by a strongly non-polar microenvironment and hindered mobility of the probe. In case of copolymers containing long pendant hydrocarbon sidechains attached to the main backbone of the hydrophobic block, the fluorescence response of C-153 is somewhat similar. However, in such systems, micellization at a unique copolymer concentration is not observed within the same concentration range as in poly(DMA-b-MMA-b-DMA), probably due to the emergence of pre-micellar aggregates.
Macromolecules, 2004
Interest is increasing in water-soluble conjugated polymers in areas such as chemical/biological sensors 1,2 and self-assembly systems. 3 In addition, introduction of ink jet printing for fabricating light-emitting diode (LED) displays 4 will increase demand for these waterbased systems. Marked changes in fluorescence occur on adding surfactants. 1b,2c Both surfactant complexation 1b and breakup of polymer aggregates 2c have been proposed as explanations. The high fluorescence yields and blue emission of polymers involving 2,7-linked fluorene units make them among the most attractive classes of conjugated polymers for devices 5 and good candidates for the above applications. We report the effect of the nonionic n-dodecylpentaoxyethylene glycol ether (C 12 E 5 ) on properties of the water-soluble poly{1,4-phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer (PBS-PFP, ). The polymer (M h n ) ∼6500 g mol -1 ) was synthesized by condensation of 2,7dibromo-9,9-bis(4-sulfonylbutoxyphenyl)fluorene (A) and 1,4-phenylenediboronic acid using Pd(PPh 3 ) 4 as catalyst.
Fluorescence enhancement of p-toluidino naphthalenesulphonate in a micellar environment
Journal of Photochemistry and Photobiology A: Chemistry, 1989
The relative fluorescence yield of p-toluidino naphthalenesulphonate increases markedly above the critical micellar concentration of Triton-X-100 and sodium dodecylsulphate. This is attributed to the reduced polarity of the hydrophobic interior of the micelles and is shown to be a simple method for following micellization.