The rubber elasticity of poly(n-isopropylacrylamide) hydrogel networks

Abstract

We report here on the characterization of classical bulk poly(N-isopropylacrylamide) (PNIPAAm) hydrogel networks. The classical PNIPAAm hydrogels were prepared from Nisopropylacrylamide (NIPAAm) as a main monomer and N,N‘-methylenebisacrylamide (MBAAm) as a crosslinker. The viscoelastic character of bulk hydrogels was examined using rheological measurements under frequency sweep mode (20 °C). A range of frequency, ? from 0.1 to 100 rad/s, was employed as this is a typical range for ‘rubber plateau’. Within this range, almost frequency independent of storage moduli (G'; ~ 104 Pa as a function of hydrogel compositions were obtained. Indeed, the ‘perfect’ soft-rubbery behaviour of PNIPAAm hydrogels could be confirmed and thus enabled the estimation of mesh size. Interestingly, the mesh size rubbery hydrogels determined from rheological data was in a good agreement to that from swelling experiments (~ 4 to 9 nm).