Swelling of carboxylated core-shell particles was caused by the addition of amine. Rheological properties of concentrated aqueous dispersion of the particles drastically change as a result of the swelling. Mechanism of the swelling of the particles has been studied by measuring the diameters of the particles in diluted aqueous dispersion neutralized by various bases. Particles with shell polymer different in hydrophobicity were prepared. Every particle contains carboxyl groups only in shell. Various dispersions with NaCl different in concentration were prepared. The diameters of the particles were determined by the dynamic light scattering method.

The diameter increases with the degree of dissociation of carboxyl group. On the other hand, it decreases with an increase in NaCl concentration, because Na⁺ and Cl_-screen the electrostatic potential of carboxylate ions. These results indicate that the swelling of the particles is caused by electrostatic repulsion between carboxylate ions of shell polymer. The diameter decreases with an increase in the hydrophobicity of shell polymer, due to the increase in the hydrophobic attraction between hydrophobic groups of the particles. This means that the hydrophobic attraction suppresses the swelling of the particles.

It is concluded that the swelling of core-shell type carboxylated acrylic particles is dominated by electrostatic repulsion and hydrophobic attraction.

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