Polymer Solutions

by Susana B. Grassino

The importance assigned to polymer solutions, a topic whose discussion has evolved from a mere informative mention in textbooks to whole books exclusively devoted to that subject, has become increasingly notorious.

The reasons are based on key factors. In the first place, the understanding of the behavior and both physical and chemical properties of macromolecules has been mainly sustained in studies carried out in solution, like for example the determination of the relative molecular mass, made by viscometry or gel permeation chromatography (GPC). On the other hand, since polymer solutions are highly viscous even at low concentrations, their commercial application includes a wide range of products, from paintings to processed foods.

Therefore, we can then consider polymer solutions as liquid mixtures made of long macromolecular chains, and small, light molecules of solvent (Grosberg and Khokhlov, 1997). This, by the way, is not a usual situation. The large size of this chains implies the employ of certain theoretical models, which should take into account, among other things, the numerous and diverse conformations that these flexible structures may assume. This particularity is not consistent with a behavior that could be regarded as an "ideal" behavior. In addition to these features, it is easily understandable that the studies performed in the evaluation of the physical-chemical properties of macromolecules are focused on dilute solutions, where the chains are separated by long distances, and therefore the interaction between them is reduced to a minimum. This is not taken for the sake of simplicity, but also because the properties of dilute solutions are governed by the properties of the individual macromolecules. In the case of concentrated solutions, the chains are entangled each other, their interaction increases, and in such conditions, the system is no longer suitable to evaluate the contribution of each macromolecule in particular.

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