Studies of dynamic interactions between a pyrene-labeled polyelectrolyte and an oppositely charged rodlike micelle by a fluorescence quenching technique with use of a hydrophobic quencher.
Electrostatic interactions of poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) (PyPAMPS) labeled with pyrene and a rodlike micelle of dimethyloleylamine oxide (DMOAO), an amine oxide type surfactant, mixed with varying mole fractions (Y) of hexadecyltrimethylammonium chloride (CTAC), a cationic surfactant, were investigated by a fluorescence quenching technique using 3,4'-dimethylbenzophenone (DBP), a hydrophobic quencher, that can only reside in the micellar phase. Fluorescence measurements were performed under homogeneous conditions in the region 0<Y<Yp, where Yp is the critical mole fraction of CTAC at which macroscopic phase separation of resulting polymer-micelle complexes occurs. There was no fluorescence quenching and hence no interaction occurred between PyPAMPS and the DMOAO/CTAC mixed micelle when Y was below a certain value (Yc) depending on the ionic strength (mu), e.g., Yc approximately 0.005 at mu=0.05. When Y>Yc, the fluorescence was efficiently quenched by DBP-carrying DMOAO/CTAC mixed micelles, both steady-state and time-dependent fluorescence data indicating that the degree of the quenching and hence the extent of the complex formation increased significantly with increasing Y. Applying a kinetic model to the steady-state and time-dependent fluorescence data, the residence time for PyPAMPS in the polymer-micelle complex was calculated. The residence time was found to depend on both Y and mu, e.g., when Y was increased from 0.01 to 0.03, the residence time increased from 4 to 80 mus at mu=0.05 whereas little or no increase in the residence time was observed in this range of Y at mu=0.20. At this higher ionic strength, the residence time increased only moderately from 3 to 10 mus when Y was increased from 0.01 to 0.09.
Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
Tatsuyoshi
T
Kawamoto
Akihito
A
Hashidzume
Yotaro
Y
Morishima