Association of Naphthalene-Labeled Poly(acrylic acid) and Interaction with Cationic Surfactants. Fluorescence Studies

Abstract

Water-soluble poly(acrylic acid) has been covalently labeled with a fluorescent hydrophobic chromophore, naphthalene (Np), randomly attached onto the polymer backbone with an amount of 3 mol %. The polymer, which is a new type of hydrophobically modified polymer denoted PAAMeNp-34, was investigated using steady-state fluorescence spectroscopy in aqueous solutions of different pH and in methanol. The fluorescence emission spectra of PAAMeNp-34 in water exhibit both Np monomer emission (with intensity IM) and Np excimer emission (with intensity IE). The excimer emission is mainly due to the association of Np groups, preformed in their ground electronic state as a result of the hydrophobic interaction. For a PAAMeNp-34 aqueous solution, the intensity ratio, IE/IM, decreases in the pH range where the electrostatic repulsive forces overcome the hydrophobic interactions between the Np groups and the polymer chain expands because of the intrapolymer repulsion between the negatively charged carboxylate groups. In...