Swelling behavior of chitosan–polyHEA hydrogels in anionic surfactant solutions and their thermo-sensitivity

Novel cationic hydrogels were synthesized on the base of water-soluble chitosan and 2-hydroxyethylacrylate (HEA) by free radical cross-linking polymerization of the latter in aqueous solution. The possible mechanism of the network formation is discussed from data on IR spectroscopy. The interaction between the chitosan–poly-2-hydroxyethylacrylate (polyHEA) hydrogel and the oppositely charged anionic surfactant, sodium dodecyl sulfate (SDS) was investigated. At lower concentration of SDS solutions, the hydrogels contract the more; the higher is the content of the chitosan. The increased swelling of the hydrogels was observed in the surfactant solutions above the critical micelle concentration due to the recharging of the network. The additional swelling effect was stronger for the hydrogels with a greater content of chitosan as well as with increase of the surfactant concentration. The complexes of hydrogels with the surfactant showed thermo-sensitive properties and contracted upon the temperature while the original networks were practically indifferent to the temperature.