Polymer association complexes, water viscosity

When a water-soluble polymer is dissolved in water, a complex network is formed that includes the polymer backbone, free water, and water in various degrees of bonding to the polymer. Depending on the concentration of polymer, its molecular weight, and several other factors, the network of polymer and bound water can assume the volume of the solution. This, of course, leads to the high viscosity that these solutions develop. The volume occupied by the polymer and the associated water in the system are said to be the hydrodynamic volume. As this volume increases because of increases in molecular weight or in the water shell surrounding the molecule, the viscosity of the solution increases. 

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