Prof. Dr. Axel Müller

The interaction of star-shaped poly(acrylic acid) having the various numbers of arms (5, 8, and 21) with a strong cationic polyelectrolyte, viz. poly(N-ethyl-4-vinylpyridinium bromide), was examined at pH 7 by means of turbidimetry and dynamic light scattering. Mixing aqueous solutions of the oppositely charged polymeric components was found to result in phase separation only if their base-molar ratio Z = [N⁺]/[COO^- + COOH] exceeds a certain critical value Z_M (Z_M < 1); this threshold value is determined by the number of arms of the star-shaped polyelectrolyte and ionic strength of the surrounding solution. At Z < Z_M, the homogeneous aqueous mixtures of the oppositely charged polymeric components contain two types of complex species clearly differing in their sizes, the fractions of these species appearing to distinctly depend on the number of arms of the star-shaped poly(acrylic acid), the base-molar ratio of the oppositely charged polymeric components in their mixtures, and the ionic strength of the surrounding solution. The small complex species (major fraction) are assumed to represent the particles of the water-soluble interpolyelectrolyte complex whereas the large complex species (minor fraction) are considered to be complex aggregates.