ABSTRACT
Hydrogel contains a large amount of water(even 99%) within a three dimensional polymer chain network.Given the paucity of the amount of the polymeric solid material, thinking of the mechanical properties as coming from the polymeric matrix does not seem reasonable: the behavior and technological characteristics of hydrogels are mainly determined by the structure and dynamics of water in contact and interacting with the polymer network.The presence of a solid interface clearly represents a major perturbation to the water as a whole, and its hydrogen-bond network. The water organization depends on the functional groups in the polymer chains. As a matter of fact, water in the hydrogel exhibits modified properties when compared to bulk water, thus the water of hydrogel has very often been divided into different classes on the basis of the different experimental techniques employed and the analysis of data.The chapter provides a multidisciplinary approach to discuss the most recent studies on the role of water in hydrogel.
