Novel responsive poly(N,N-dimethylaminoethyl methacrylate) gel beads: preparation, mechanical properties and pH-dependent swelling behavior

pH-responsive gels have become of major interest because stimuli-responsive polymers are increasingly used in a number of new applications. pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) gel beads crosslinked with N,N'-methylene(bisacrylamide) (BAAm) were prepared by addition of the frozen monomer solution into the paraffin oil as continuous phase. The resulting spherical millimeter-sized PDMAEMA gel beads were well characterized by the swelling and elasticity tests. The uniaxial compression measurements were carried out using 27 gel beads of various diameters. The elastic modulus of equilibrium swollen beads were calculated using Hertz theory and the results showed that the swollen modulus G decreases with increasing bead diameter. The equilibrium swelling degree of PDMAEMA gel beads were investigated as a function of pH of the solution. It was found that PDMAEMA gel beads are pH-sensitive at pH of about 8.0. The resulting gel beads first remain in the swollen state up to pH 7.7, then exhibit sharp pH-dependent phase transition at 8.0 in which the gel beads attain a collapsed state. The large extent of the volume transition from the swollen hydrophilic state to the collapsed hydrophobic state makes this system as the most extensively studied class of smart gels.