Molecular weight distribution polymer adsorption isotherms

One final way in which to reduce the amount of polymer in solution is to use a narrow molecular weight distribution. It is well known that narrow distributions give sharper adsorption isotherms. Commercial polymers are made by free... 

Felter RE, Ray LN. Polymer adsorption studies at the solid-liquid interface using gel permeation chromatography. 1. Molecular weight distribution along the adsorption isotherm. J Colloid Interface Sci 1970 32 349-360. 

If a mixture contains more than two fractions the treatment can easily be generalized. For example, a trimodal mixture gives four linear isotherm sections ). The Increasing part of fig. 5.29 is replaced by two sections of different slope in the first the lowest molecular weight is displaced from the surface, in the second the middle fraction. For a continuous distribution of molecular weights a rounded isotherm is obtained the adsorption fractionation varies smoothly with the polymer dose. 

As an illustration. Figure 14.5 shows the adsorption isotherms at 25°C for PVA (containing 12% acetate groups) on polystyrene latex [18]. The figure shows the high-affinity isotherms for the polymers and the increase in adsorption of the polymer with increase of the molecular weight. Similar isotherms are expected for the adsorption of the polymer on oil droplets. However, in the latter case it is not possible to obtain the full isotherm, since to produce the emulsion one requires a minimum amount of polymer. In addition, the surface area of the emulsion has to be determined at each point from the droplet size distribution. 

The adsorption isotherms of dextranes, polyethylene glycols and polystyrenes from dilute solution have been studied for porous silica and carbon sorbents. The dependences of maximum adsorption values on the molecular weight of these polymers have been analysed. These dependences have been used for the calculation of surface areas and pore volume distributions. 

---