Novel Method to Monitor the De-Swelling of PNIPAAm Hydrogels of Different Cross-Link Density

Abstract

The effect of cross-linker (methylene-bis-acrylamide) (MBA) on the volume phase transition, mechanical properties and de-swelling of Poly(N-isopropyl acrylamide-co-methylene-bis-acrylamide) hydrogel (PNIPAAm/MBA hydrogel) was investigated. A new method, namely isothermal thermogravimetry was developed for monitoring de-swelling of PNIPAAm/MBA hydrogel. Monomer/ Cross-linker ratio of the initial monomer composition R = moleNIPAAm/moleMBA was introduced. It has been proven earlier that initial monomer composition is close to the copolymer composition; hence R values may be used to express cross-link density. Hydrogels from R10 to R150 were investigated. The results of DSC analysis revealed that the less the cross-linker ratio in the gel (from R10 to R150) the more sharp the temperature range of volume phase transition and the higher its enthalpy...