PH-stimulus on–off switching behavior and improved response rate of slightly charged poly(N,N-dimethylaminoethyl methacrylate) nano-sized composites with incorporated Laponite as crosslinker

Abstract

pH-responsive poly(N,N-dimethylaminoethyl methacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid)/Laponite (P(DMAEMA-co-AMPS)/Lap) nano-sized composite (NC) hydrogels and cryogels were prepared by in situ free radical polymerization of DMAEMA and AMPS in an aqueous solution with inorganic clay Laponite (Lap) as a crosslinker. pH-dependent swelling properties as well as the elasticity of P(DMAEMA-co-AMPS)/Lap nano-sized composite (NC) hydrogels and cryogels were investigated and the parameters of swelling and diffusion of water in buffer solutions were evaluated as a function of the Lap content. The uniaxial compression measurements exhibited good elastic properties and the nanostructure of NC gels improved the gel strength, while the swelling ratio depended on synergic effects of multifunctional groups. P(DMAEMA-co-AMPS)/Lap NC cryogels exhibit higher elastic modulus than that of the corresponding NC hydrogels over the entire range of the pH. As expected from the protonation of the DMAEMA monomer, P(DMAEMA-co-AMPS)/Lap NC gels showed pH-responsive swelling and were swollen at pH<7.7 and shrunken at pH>8.0. This work provides a simple method for fabricating pH-responsive nano-sized composite hydrogels and cryogels with superior mechanical property.