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Trends in Photochemistry & Photobiology   Volumes    Volume 7 
Excited state transients and interactions within micellar systems
Ignac Capek
Pages: 147 - 157
Number of pages: 11
Trends in Photochemistry & Photobiology
Volume 7 

Copyright © 2001 Research Trends. All rights reserved


This article presents studies based on using fluorescence probes within the micelles, the monomer-swollen micelles (microdroplets), polymer particles and the interfacial layer. Pyrene (Py) as a probe is particularly attractive because of its ability to measure the polarity of its microenvironment and its tendency to form excimers with a distinct red shifted fluorescence. Some probes like laurdan and prodan can be used to explore the surface characteristics of micelles or microdroplets. The dansyl group (dimethylamino group covalently bound to napthalene moiety) has a special photophysical property that gives information about the local polarity  and mobility (viscosity) of the microenvironment. Dipyme (bis(l-pyrenylmethyl) ether) is proved to be an effective probe to measure both the local polarity and viscosity. The probe investigations show that the oil-water interfacial layer of microdroplet can provide the common domain for reactants with different hydrophobicity. The heterogeneity in the local concentration can also result from the attractive interaction between hydrophilic monomer and emulsifier in the case when monomer carries a positive charge and the counterpart the negative one and vice versa. The noncooperative interaction between micelles (microdroplets) and charged polymers leads to the formation of mixed micelles. Binding emulsifiers to these polymers was detected at emulsifier concentrations much below the CMC. Emulsifiers often interact cooperatively with polymers at the critical aggregation concentration below CMC forming micelle-like aggregates within the polymer. In the emulsion polymerization, the particle nucleation is assumed to depend on the interaction (cooperative or noncooperative) of polymeric (oligomeric) radicals with emulsifier or micelles. The decrease in the monomer fluorescence intensity of probe-labelled polymer results from the increased excimer emission within the unimolecular polymeric micelles. On the contrary, the increase in the monomer fluorescence intensity of probe-labelled polymer within the micellar system can be ascribed to shielding the probe chromophores by emulsifier micelles. The quenching of probe emission by (un)charged hydrophilic monomer depends on the partitioning of monomer between the aqueous phase and the micelles. Furthermore, the extent of penetration of reactants into the interfacial layer governs quenching of hydrophobic probe molecules (or initiation) by hydrophilic quencher or vice-versus. The quenching events are proportional to the thickness and density of interfacial layer.

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