ABSTRACT
Morphological change of a micelle of poly(styrene)-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) (PS-PVP-PEO) polymer was induced by binding sodium dodecyl sulfate (SDS) to the PVP block in acidic aqueous solutions. The change in the size of SDS/PS-PVP-PEO complexes was detected by dynamic light scattering measurements and atomic force microscopy, and the binding of SDS was confirmed by zeta-potential measurements. When the micelle was free from SDS in acidic aqueous solutions, the hydrodynamic diameter of the micelle was 216 nm, reflecting the extended conformation of the PVP block due to the repulsion between protonated pyridine units. As the cationic PVP block was electrically neutralized with anionic SDS, the diameter was gradually reduced concomitant with the decrease in zeta-potential and finally reached 175 nm when the PVP block was completely neutralized. The decrease in the diameter shows the morphological change of the PVP block from extended to shrunken forms. Further addition of SDS did not cause the changes of the diameter nor zeta-potential. This indicates that SDS was not bound to the PS-PVP-PEO polymer after the PVP block was fully neutralized and that the hydrophobic binding of SDS to the polymer was negligible due to the low concentration of SDS.
ABSTRACT
The binding of a photosurfactant, 4-butyl-azobenzene-4'-oxyethyltrimethyl ammonium bromide (BZTABr), to a linear polymer, sodium poly(2-acrylamide-2-methylpropane sulfonate) (PAMPS), has been studied by using a surfactant selective electrode. The photosurfactant undergoes a trans-cis transition on UV/vis irradiation. The binding behavior changes by varying the composition of the trans and cis forms in the solution. The ideal mixing-ideal cooperative binding model we had proposed previously for the binding of binary surfactants was applied to successfully predict the binding isotherms and the critical aggregation concentrations of the present systems. The binding of a trans-cis mixture of BZTABr to a polymer is analogous to the ideal mixed micelle formation. A sort of synergetic effect was found in the binding process. Copyright 1999 Academic Press.