The stability of colloidal suspensions is significantly influenced by the particle size and charge. In general, smaller particles with higher surface charges lead to more stable colloidal suspensions. This is due to the increased repulsive forces between the particles, which prevent them from aggregating and settling out of the suspension.1. Effect of particle size:The stability of colloidal suspensions is influenced by the Brownian motion of particles, which is the random movement of particles due to collisions with solvent molecules. Smaller particles have a higher Brownian motion, which helps to keep them dispersed in the suspension. As the particle size increases, the Brownian motion decreases, and the particles are more likely to aggregate and settle out of the suspension due to gravitational forces.Experimental evidence: In a study by Kusters et al. 1991 , the effect of particle size on the stability of colloidal suspensions was investigated. They found that smaller particles around 1 m had a higher stability compared to larger particles around 10 m . The smaller particles remained dispersed in the suspension for a longer time, while the larger particles aggregated and settled out of the suspension more quickly.2. Effect of particle charge:The charge on the surface of colloidal particles plays a crucial role in determining the stability of the suspension. Charged particles create an electric double layer around them, which results in repulsive forces between the particles. The higher the surface charge, the stronger the repulsive forces, and the more stable the colloidal suspension.Experimental evidence: In a study by Derjaguin and Landau 1941 and Verwey and Overbeek 1948 , known as the DLVO theory, the effect of particle charge on the stability of colloidal suspensions was investigated. They found that when the surface charge of the particles was increased, the repulsive forces between the particles also increased, leading to a more stable suspension. Conversely, when the surface charge was reduced, the particles were more likely to aggregate and settle out of the suspension due to attractive van der Waals forces.In conclusion, both particle size and charge play crucial roles in determining the stability of colloidal suspensions. Smaller particles with higher surface charges result in more stable suspensions due to increased Brownian motion and repulsive forces between the particles. Experimental evidence from studies like those by Kusters et al. and the DLVO theory support these observations.