Aggregation numbers and microstructure characterization of self-assembled aggregates of poly(ethylene oxide) surfactants and related block-copolymers, studied by spectroscopic methods.

This review presents typical examples of micellar size measurements and structural characterization of self-assembled systems as determined with spectroscopic methods, selected from our representative results accumulated in recent years of systematic studies. The choice of examples has aimed at emphasizing the potentiality of the methods used in the study of poly(ethylene oxide) (PEO) surfactants. By using the time-resolved fluorescence quenching method aggregation numbers have been determined for direct and reverse micelles as well as for micelle-like clusters formed in (bio)polymer-surfactant solutions. By using specific spectral parameters of a variety of properly chosen molecular probes [fluorescence, UV-VIS and electron spin resonance (ESR) spin probes], problems such as hydration degree and profile of the PEO chains, local viscosity, ordering and packing of surfactant chains have been addressed. The intention was to correlate results obtained from different spectroscopic methods and to refer all polarity data to a common scale, such as Kosower's polarity factor.