Key points are not available for this paper at this time.
The large-amplitude oscillatory shear (LAOS) behavior of poly(vinyl alcohol) (PVA)/borate hydrogels was investigated with the change of scanning frequency (ω) as well as concentrations of borate and PVA. The different types (Types I–IV) of LAOS behavior are successfully classified by the mean number of elastically active subchains per PVA chain (feas) and Deborah number (De = ωτ, τ is the relaxation time of sample). For the samples with Type I behavior (both storage modulus G′ and loss modulus G″ increase with strain amplitude γ, i.e., intercycle strain hardening), the critical value of strain amplitude (γcrit) at the onset of intercycle strain hardening is almost the same when De > ∼2 (Region 3), while the value of Weissenberg number (Wi = γDe) at γcrit is similar when De 1. In Region 3, strain-induced non-Gaussian stretching of polymer chains results in both intercycle and intracycle strain hardening. In Region 2 (∼0.2 1.
Huang et al. (Fri,) studied this question.