Modelling the mechanical behaviours of glassy hydrogels

Abstract Our recent works show that poly(methacrylamide- co -methacrylic acid) (P(MAAm- co -MAAc)) hydrogels with moderate water content (50–70 wt%) exhibit similar glass transition behaviours as in dry polymers. In the glassy state, these gels exhibit a modulus of several hundred megapascals and a failure strength of tens of megapascals, which are much higher than other reported tough gels. In this work, we apply a viscoplastic model to describe the temperature-dependent and rate-dependent mechanical behaviours of the P(MAAm- co -MAAc) gels. It is found that the viscoplastic model developed for dry polymers can also describe the stress-strain responses of gels including yielding and strain softening. It can also capture the stress relaxation behaviours. This work confirms that the glass transition in the gels and dry polymers shares a similar physical mechanism. Meanwhile, it indicates the classic viscoelastic/viscoplastic models can be readily applied for this new type of tough gels.