This lecture discusses the incompatibility of different polymers in the same solvent and the stability of colloidal dispersions stabilized by polymer chains. The potential of average force, \( V(r) \), and the second virial coefficient, \( B_2 \), are key factors in understanding these systems. The lecture covers the following main points: 1. **Incompatibility and Colloid Stability**: Solutions of different polymers in the same solvent typically show phase separation due to incompatibility. The entropy of mixing is small, while the energy of mixing is significant, leading to phase separation. 2. **Thermodynamic Criteria for Colloid Stability**: Thermodynamic criteria are used to describe polymer solutions and colloidal dispersions, including phase separation. The effective forces between colloidal particles can be described using statistical thermodynamics. 3. **Volume Restriction and Osmotic Effects**: When polymer chains are attached to particle surfaces, they lose configurational entropy when approaching other particles, leading to "volume restriction" effects. This results in a repulsive force between particles. Additionally, the osmotic pressure between the polymer layers can counteract the approach of particles, leading to "osmotic" effects. 4. **Mixtures of Marked and Unmarked Particles**: The lecture discusses how the effective interactions between particles are affected by the presence of other particles. The second virial coefficient and adsorption of one particle on another are calculated using thermodynamic relations. 5. **Experimental Evidence**: The lecture presents experimental results on the creaming rate of latex, flocculation of sterically stabilized latex, and microemulsion with added polymer. These experiments support the theoretical predictions of destabilization due to added polymer. 6. **Light Scattering of Polymer Colloids**: Light scattering experiments are used to determine the second virial coefficient and adsorption of one component on another in polymer colloid mixtures. The results are consistent with the theoretical predictions. The lecture concludes by emphasizing the importance of light scattering as an experimental tool in studying the stability of polymer colloidal dispersions.This lecture discusses the incompatibility of different polymers in the same solvent and the stability of colloidal dispersions stabilized by polymer chains. The potential of average force, \( V(r) \), and the second virial coefficient, \( B_2 \), are key factors in understanding these systems. The lecture covers the following main points: 1. **Incompatibility and Colloid Stability**: Solutions of different polymers in the same solvent typically show phase separation due to incompatibility. The entropy of mixing is small, while the energy of mixing is significant, leading to phase separation. 2. **Thermodynamic Criteria for Colloid Stability**: Thermodynamic criteria are used to describe polymer solutions and colloidal dispersions, including phase separation. The effective forces between colloidal particles can be described using statistical thermodynamics. 3. **Volume Restriction and Osmotic Effects**: When polymer chains are attached to particle surfaces, they lose configurational entropy when approaching other particles, leading to "volume restriction" effects. This results in a repulsive force between particles. Additionally, the osmotic pressure between the polymer layers can counteract the approach of particles, leading to "osmotic" effects. 4. **Mixtures of Marked and Unmarked Particles**: The lecture discusses how the effective interactions between particles are affected by the presence of other particles. The second virial coefficient and adsorption of one particle on another are calculated using thermodynamic relations. 5. **Experimental Evidence**: The lecture presents experimental results on the creaming rate of latex, flocculation of sterically stabilized latex, and microemulsion with added polymer. These experiments support the theoretical predictions of destabilization due to added polymer. 6. **Light Scattering of Polymer Colloids**: Light scattering experiments are used to determine the second virial coefficient and adsorption of one component on another in polymer colloid mixtures. The results are consistent with the theoretical predictions. The lecture concludes by emphasizing the importance of light scattering as an experimental tool in studying the stability of polymer colloidal dispersions.