作者：G. Huang, H. Zhang, Y. Liu, H. Chang, H. Zhang, H. Song, D. Xu, and T. Shi
关键字：Strain Hardening, Hydrogels
论文来源：期刊
具体来源：Macromolecules
发表时间：2017年

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 < ～0.2 (Region 1). For intracycle behavior in the Lissajous

curve, intracycle strain hardening is only observed in viscous Lissajous curve of Region 1 or in the elastic Lissajous curve of

Region 3. In Region 1, both intercycle and intracycle strain hardening are mainly caused by the strain rate-induced increase in the

number of elastically active chains, while non-Gaussian stretching of polymer chains starts to contribute as Wi > 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 < De < ～2), two involved mechanisms both contribute to intercycle strain hardening. Furthermore, by analyzing the

influence of characteristic value of De as 1 on the rheological behavior of PVA/borate hydrogels, it is concluded that intercycle

strain hardening is dominated by strain-rate-induced increase in the number of elastically active chains when De < 1, while straininduced

non-Gaussian stretching dominates when De > 1.