Rheological Behavior of Tough PVP-in Situ-PAAm Hydrogels Physically Cross-Linked by Cooperative Hydrogen Bonding

Abstract

Rheology studies were performed on tough PVP-in situ-PAAm hydrogels physically cross-linked by cooperative hydrogen bonding to understand their viscoelastic response and, hence, the interactions and microstructure. The viscoelasticity of the PVP-in situ-PAAm hydrogels was strongly affected by the monomer ratio (C AAm /C VP ). Hydrogels prepared with a high monomer ratio exhibited weak time, temperature and frequency dependence of the viscoelastic properties, similar to those of chemically cross-linked hydrogels. The storage modulus (G′) of the gels was much greater than the loss moduli (G″) and low loss factor (tan δ < ∼ 0.1), which indicated that they were solid-like, and mostly elastic. These supramolecular gels exhibited a strain-and C AAm /C VP -dependent reversible gel (solid) to viscoelastic liquid transition due to the dynamic nature of the cooperative hydrogen bonds. That transition also coincided with the onset of nonlinear viscoelastic behavior. The addition of a low molecular weight compound, urea, that competes for hydrogen bonding sites weakens the gel by decreasing the effective cross-link density or weakening the intermolecular hydrogen bonding.

Synthesis of poly(acrylic acid)–Fe3+/gelatin/poly(vinyl alcohol) triple‐network supramolecular hydrogels with high toughness, high strength and self‐healing properties

“…According to the calculation of the equation tan δ = G ″/ G ′, tan δ values at smaller strain ( γ = 1%) and larger strain ( γ = 100%) are 0.13 and 1.3, respectively. This indicates that the hydrogel experiences a transition from original quasi‐solid state to a quasi‐liquid state . It can be observed that the G ′ and G ″ values can immediately recover the initial values and the sample returns to the original quasi‐solid state.…”

“…. For all hydrogels, G ′ is much larger than G ″ over the entire frequency range, revealing the solid‐like elastic nature of the gel . At low frequency, the G ′ value increases as the frequency increases, while there is an almost frequency‐independent G ′ value at high frequency.…”

In Situ Network Formation in PBT Vitrimers via Processing‐Induced Deprotection Chemistry

“…The solid‐like mechanical responses of the cured materials were also demonstrated by the frequency dependence of the complex viscosity (|η*|, Pa⋅s). Linear relationships between log |η*| and log ω with a slope of −1 were observed (Figure A), and this behavior corresponds to a perfectly elastic solid, such as an ideal chemically cross‐linked network …”

Highly Mechanical and Fatigue‐Resistant Double Network Hydrogels by Dual Physically Hydrophobic Association and Ionic Crosslinking

“…Figure b showed the frequency sweep data of the HPAAm hydrogel, HPAAm/alginate hydrogel, and HPAAm/alginate‐Ca 2+ DN hydrogel. All hydrogels showed G′ was much larger than G′′ which indicated hydrogels possessed a predominantly solid‐like state, and the G′ was frequency independent in the entire frequency range . The G′ of the HPAAm/alginate‐Ca 2+ DN hydrogel was larger than the HPAAm hydrogel and HPAAm/alginate hydrogel, since the introduction of Ca 2+ ionic crosslinked with alginate and forming the double network that improve the G′ of HPAAm/alginate‐Ca 2+ DN hydrogel.…”