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Dynamical Relaxations of Cross Linked Networks in Polymer Solutions

Mustapha Benmouna and Farida Benmouna*

Cross linked polymer networks and gels have been the subject of a particular attention in the literature for decades not only because of their fundamental interest but also because of their applications [1]. The presence of crosslinks leads to a physical behavior differing from that of pure free chain systems due to interplay between hard and soft properties. They combine the elasticity of polymer chains and the solidity of the assembly of strands holding together with covalent bonds. They can absorb large amounts of a low molecular weight good solvent (water in the case of hydrogels) undergoing substantial swelling. They also contract by expelling the solvent under certain conditions. Contraction and swelling are governed primarily by the nature of constituents in the medium, environmental conditions or external perturbations. The crosslinking density determines the mean size of the polymer strand between consecutive crosslinks and plays a major role in the solvent uptake or degree of de-swelling. In addition to low molecular weight solvents, networks have the ability to sequestrate macromolecular species such as DNA, proteins and enzymes. This property has extended the area of interest of cross linked networks and opened up new opportunities triggering intensive research work in recent years [1]. Most efforts focus on attempts to elucidate the impact of relevant parameters and multicomponent interactions within the system. Gene therapy and drug delivery based on encapsulated DNA, protein or drugs, highly sensitive smart devices are among the applications where one needs to understand the behavior of cross linked networks embedded in macromolecular solutions