The Bridging Force between Colloidal Particles in a Polyelectrolyte Solution

The presence of a polyelectrolyte in a colloidal dispersion affects the interaction between colloidal particles through electrostatic and bridging interactions. In this paper, using a self-consistent field approach, a simple theory is developed which allows for the calculation of the bridging force between two plates and two colloidal particles. The present approach differs from the previous ones, since the contribution of the plate-solution interfacial tension to the free energy is taken into account in the calculation. The interfacial tension between solvent and plate depends on the nature of the particles and the concentration of the segments of the polymer at the surface. The surface segment interaction has a significant effect on the segment concentration profile. When the segment surface interaction is repulsive, the bridging force is weak because few polyelectrolyte chains are adsorbed onto the surface. When the segment surface interaction is attractive, various segment concentration profiles could be identified. Depending upon the concentration of polyelectrolyte, the electrostatic plus bridging forces can be attractive or repulsive. The bridging force between two plates which is attractive has a longer range than the van der Waals interaction.