EPR spin probe and spin label studies of some low molecular and polymer micelles

The rotational mobility of spin probes of different shape and size in low m olecular and polymer micelles has been studied. Several probes having nitro xide fragment localized either in the vicinity of micelle interface or in t he hydrocarbon core have been used. Upon increasing the number of carbon at oms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate mi celles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rota tional mobility of spin probes is decreased by the factor 1.5-2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrime thylammonium bromides and polymethacrylic or polyacrylic acids) is less tha n mobility in free micelles of the same surfactants. The study of EPR-spect ra of spin labeled polymethacrylic acid (PMA) indicated that formation of w ater soluble complexes of polymer and alkyltrimethylammonium bromides in al kaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water so lution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are di scussed. (C) 1998 Elsevier Science B.V. All rights reserved.