Fluorescence analysis, polymer dynamics

There continues to be extensive interest in latexes and micellar systems. The structure of acrylic latex particles has been investigated by non-radiative energy transfer by labelling the co-monomers with fluorescent acceptor-donor systems. Phase separations could also be measured in this way. Excimer fluorescence has been used to measure the critical micelle temperature in diblock copolymers of polystyrene with ethylene-propylene and the results agree well with dynamic light scattering measurements. Fluorescence anisotropy has been used to measure adsorption isotherms of labelled polymers to silica as well as segmental relaxation processes in solutions of acrylic polymers. In the latter case unusual interactions were indicated between the polymers and chlorinated hydrocarbon solvents. Fluorescence analysis of hydrophobically modifled cellulose have shown the operation of slow dynamic processes while fluorescence... 

All OFDs reported in the literature suffer from spectral interferences, long response times, and narrow dynamic responses. Many of these obstacles exist as a result of limitations due to the properties of UY/visible fluorescent dyes. These dyes typically absorb and fluoresce between 300 and 650 nm, a region susceptible to extensive interference, especially from biomolecules (Figure 7.1). The fluorescence of sample impurities combined with the inner effect of the matrix and polymer support greatly increase the signal interference of the analysis. 

Several interesting theoretical papers have appeared dealing with molecular dynamics and excimer formation in polymer systems. Frank and coworkers have developed a model to describe the transport of electronic excitation energy in polymer chains. The theory applies to an isolated chain with a small concentration of randomly placed chromophores, and a three-dimensional transport model was used to solve the problem which is based on a diagrammatic expansion of the transport Green function. (The Green function is related to time-dependent and photostationary depolarization and to transient and steady-state trap fluorescence.) The analysis is shown to be... 

Analysis of the fluorescence decay curves in water indicated that the intracoil process is static and that anthryl aggregation induces non-exponentiality in the fluorescence decay associated with a dynamic equilibrium between the singlet diphenyl-anthracene and a non-fluorescent dimer state. Further evidence was also presented to show that these polymers self-organise into hydrophobic and hydrophilic regions Energy migration in alternative and random copolymers of 2-vinylnaphthalene and methyl methacrylat methacrylic acid... 

Time-resolved fluorescence spectroscopy and fluorescence anisotropy measurements have been applied to study (i) excimer formation and energy transfer in solutions of poly(acenaphthalene) (PACE) and poly(2-naphthyl methacrylate) (P2NMA) and (ii) the conformational dynamics of poly(methacrylic acid) (PMA) and poly (acrylic acid) as a function of solution pH. For PACE and P2NMA, analysis of projections in which the spectral, temporal and intensity information are simultaneously displayed have been used to re-examine kinetic models proposed to account for the complex fluorescence decay behaviour that is observed. Time-resolved fluorescence anisotropy measuranents of fluorescent probes incorporated in PMA have led to the proposal of a "connected cluster" model for the hypercoiled conformation of this polymer existing at low pH. 

The absorption of light by the diphenylanthracene was found to result in efficient intracoil sensitization by fluorescene. The quantum efficiency of this process was determined to be 0.4 in methanol and 0.8 in water. This increase corresponds to a decrease in polymer coil size in water. Analysis of the fluorescence decay also demonstrates that the intracoil energy transfer is essentially a static process and that aggregation can result in nonexponential fluorescence decay that is interpreted as a dynamic equilibrium that takes place between diphenylanthracene and a nonfluorescent dimer state... 

Fluorescence anisotropy studies of concentrated solutions are important for two reasons. Firstly, they bridge the gap between the results for dilute solutions, which can be interpreted relatively easily on the basis of the existing models, and the practically important dynamic behavior of bulk polymers, which is very complicated and its theoretical description and appropriate analysis are difficult. SecOTidly, they elucidate the contribution of the local frictirai to the macroscopic viscosity rj c,T,M) of concentrated polymer solutions. The viscosity coefficient where c is the polymer concentration, M is its molar mass, and T is temperature, can be expressed as... 

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