High tensibility and pH-responsive swelling of nanocomposite hydrogels containing the positively chargeable 2-(dimethylamino)ethyl methacrylate monomer

Positively chargeable nanocomposite hydrogels (NC gels) were synthesized by in situ copolymerization of acrylamide (AM) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in an aqueous suspension of hectorite clay Laponite XLS. The stability of the Laponite suspension containing DMAEMA was monitored by its transmittance, viscosity and zeta potential. The polymerization was initiated either by redox or UV radiation to fabricate the NC gels. Elongation at break and tensile strength decreased with increasing DMAEMA content in monomers up to 17 mol%. As expected from the protonation of DMAEMA, the NC gels containing more than 5 mol% DMAEMA showed pH-responsive swelling; the gels were swollen at pH < 4 and shrunken at pH > 4. In comparison with the redox-initiated NC gels, the UV-initiated NC gels possessed a more homogeneous structure with higher transmittance, better mechanical properties, and a larger equilibrium swelling ratio at pH < 4.