TABLE OF CONTENTS As discussed in Chapter 4, polymer molecules consist of many segments that usually have considerable degrees of freedom. In solution, they behave different from other surfactants having more or less random coils. When such coils adsorb on the surface, the conformation of the molecules changes, depending on the balance between entropy and energy. For a low concentration of polymer in solution, it is believed that the adsorbed chain lies flat on the surface, but in a solution of finite concentration the adsorbed layer may have considerable thickness with parts of each chain extending into solution. Therefore, the models used to explain adsorption of low molecular-weight substances (i.e. Langmuir model) has no meaning for adsorption of polymers. Normally, any adsorption theory for polymers should account for its specific characteristics. Because the polymers are hetero-dispersed with a wide molecular-weight distribution, the characterization of the adsorption layer is rather difficult. In spite of the fairly large amount of data in the literature, much of this material cannot be interpreted because the relevant variables are not controlled or are simply unknown.
In many studies, the hetero-dispersed polymers are compared with homo-dispersed polymers with the same average molecular-weight distribution in the real sample. Such an assumption breaks down completely for adsorption measurements since as a result of strong preferential adsorption of long chains, the average molecular weight of the adsorbed material is very different from that in the solution. These implications have been included in interpretations of the experimental data.
Theoretical aspects of...
