Total colloidal stability ratio

Einarson and Berg (1993) have attempted to explain the data on flocculation kinetics of latex particles with a block copolymer adsorbed on them. The polymer was polyethylene oxide (PEO)/polypropylene oxide (PPO). PPO is water insoluble and forms the part that adsorbs on the latex PEO forms streaming tails into water. Some charge effects remain after the polymer adsorption. The total potential is DLVO plus elastic plus osmotic effects. After fitting the model to the experimental data, they were able to calculate the value of 6, which they called the adlayer thickness. Their data on the stability ratio of latex with and without the polymer and as a fimction of NaCl concentration are shown in Figure 3.23. Note that the polymer stabilizes the colloid by almost one order of magnimde in NaQ concentration. That is, polymers may be necessary to maintain stability in aqueous media containing substantial electrolyte. 

As we introduced in the preceding section, colloidal systems are stabilized by a delicate balance of competing forces. These forces either act to repel the colloidal particles from each other or mutually attract them into aggregates. Colloidal particles are small, and as a result a colloidal system can have an extremely high surface area-to-volume ratio. Consider a 1-cm cube of gold the surface area-to-volume ratio of the cube is 6 cm /l cm. Now, if we take that same cube of gold but split it into 10-nm wide cubes, the total surface area-to-volume increases to 6 X 10 cm /1 cm. This calculation shows that as particle size decreases, the surface interactions between particles increase in importance and tend to dominate the physics of the system at very small particle sizes. 

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