Thermo-responsive sandwiched-like membranes of IPN-PNIPAAm/PAAm hydrogels

Abstract

The synthesis of sandwiched-like IPN hydrogels having cross-linked PNIPAAm interpenetrated into PAAm networks was carried out by UV-induced polymerization using potassium periodate as a sensitizer. NIPAAm monomers and MBAAm cross-linker were co-polymerized inside previously synthesized cross-linked PAAm. Through SEM images, we observed that the hydrogel membranes were formed by three layers; the internal layer was fully involved by the two others. Significant morphological difference between the internal and external layers was also observed. Thus, sandwiched-like interpenetrating polymer networks were obtained. The internal layer shrank significantly after warming the swollen hydrogel above LCST of PNIPAAm in water, 30–35 °C while the external layers remained swollen and highly porous due to the hydrophilicity of PAAm. The experiments performed at 40 °C revealed that the hydrogels shrank considerably. Collapsed PNIPAAm chains induced a substantial contraction of the internal hydrogel layer. The hydrogel contraction was accompanied by an increase in gel strength and elasticity modulus. The presence of the PNIPAAm network in the internal layer reinforced the hydrogel and this effect was more pronounced above LCST. The permeability of sandwich-like membrane significantly rather decreases as the temperature increases. There was a decrease in the permeability of 52% as the temperature was increased from 25 to 40 °C. It was suggested that the structural changes in the sandwich membrane induce to significant flux control.