Mechanical and Rheological Behavior of Hybrid Cross‐Linked Polyacrylamide/Cationic Micelle Hydrogels

Abstract

with an ionic cross-linking alginate-Ca 2+ network, which exhibit highly stretchable property of beyond 20 times their initial length and remarkable fracture energy of nearly 9 kJ m −2 . [15] Chen et al. engineered hybrid Agar/PAM hydrogels, which exhibited high stiffness of 313 kPa and high toughness of 1089 J m −2 . [16] They also fabricated fully physical cross-linking DN hydrogels combing Agar with hydrophobic associated PAM, which showed rapid selfrecovery and self-healing properties at room temperature. [17] Besides, integrating the covalent bonds and physical bonds into a single network has attracted more and more attention. Hu et al. prepared PAM/ carbon nanodot hybrid hydrogels using carbon nanodot as physical cross-linker. The fabricated hydrogel, even in the swelling equilibrium state, keeps extraordinary mechanical and recoverable properties. [18] Xie and co-workers synthesized poly(acrylic acid) hybrid hydrogels by introducing ionic cross-linking interaction between Fe(III) and carboxyl groups into the chemical cross-linking network, and the resulting hydrogels achieve tensile stress of ≈1.07 MPa and toughness of ≈11.7 MJ m −3 . [19] In these network structures, the covalent cross-linking preserved the initial state of the network and the recoverable physical cross-linking could well disperse the stress concentration during deformation process, resulting in excellent mechanical property of these hydrogels. However, these hydrogels presented apparently poor elasticity and large residual strain after cyclic tensile test. Therefore, fabricating hydrogels simultaneously owing high toughness and elasticity remains a challenge.Molecular self-assembly behavior plays an important role in biological systems. [20] For example, cell membranes share a common structure of phospholipid bilayers, formed by the self-assembly of amphiphilic molecules. Besides, amphiphilic molecules can also form a variety of self-assembled morphologies, such as micelles, hexagonal, and cubic phases, which have been attracting significant attention for the purpose of fabricating tough hydrogels. Interesting examples are presented by the hydrogels crosslinked by micelles. [21,22] In such hydrogels, crack energy can be efficiently dissipated by flexible dislocation of polymeric micelles along with the chain slippage, leading to highly stretchable and excellent resilience of hydrogels. [21] As a result, it was envisioned that the combination of covalent bonds and physical interactions from self-assembled micelles is a viable method to prepare hybrid hydrogel with extraordinary mechanical performance. HydrogelsIn this work, a hybrid cross-linked polyacrylamide (PAM)/cationic micelle hydrogel is fabricated by introducing the cationic micelles into the chemically cross-linked PAM network. The cationic micelles act as the physical cross-linking points through the strong electrostatic interaction with anionic initiator potassium persulfate. Thereafter, in situ free radical polymerization is initiated thermally from the cationic micelle surfac...

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

“…Moreover, the critical strain value of the HPAAm/alginate‐Ca 2+ DN hydrogel was smaller than the other two hydrogels. This indicated that the crosslinking density of the HPAAm/alginate‐Ca 2+ DN hydrogel was higher than the other two hydrogels, owing to the critical strain decreasing with the increasing of crosslink density for the network . These results are in accordance with the results obtained from the stress–strain curves.…”

“…This indicated that the crosslinking density of the HPAAm/alginate-Ca 2+ DN hydrogel was higher than the other two hydrogels, owing to the critical strain decreasing with the increasing of crosslink density for the network. [33,34] These results are in accordance with the results obtained from the stress-strain curves. Figure 9b showed the frequency sweep data of the HPAAm hydrogel, HPAAm/alginate hydrogel, and HPAAm/alginate-Ca 2+ DN hydrogel.…”

MWCNTs reinforced conductive, self‐healing polyvinyl alcohol/carboxymethyl chitosan/oxidized sodium alginate hydrogel as the strain sensor

“…Rheological properties are very important criteria for determining the three‐dimensional structure of the crosslinked polymer molecular chains 42 . Figure 3(e,f) showed the changes of storage and loss modulus of hydrogels with different contents of OMWCNTs in the frequency range of 0.1–100 rad/s, respectively.…”

“…Rheological properties are very important criteria for determining the three-dimensional structure of the crosslinked polymer molecular chains. 42 Figure 3(e,f) showed the changes of storage and loss modulus of hydrogels with different contents of OMWCNTs in the frequency range of 0.1-100 rad/s, respectively. In the test region, the storage modulus (G 0 ) of all these hydrogels with or without OMWCNTs were much higher than their loss modulus(G 00 ), which implied the good elastic behavior of the composite hydrogels.…”

Supramolecular hydrogels prepared from fluorescent alkyl pyridinium acrylamide monomers and CB[8]

“…57 The AAm control hydrogel presented a less pronounced strain overshoot, which has been observed by others. 58,59 This behaviour, observed in AAmbased hydrogels, may be related to the presence of an additional structure associated by hydrogen bonding that imposes some resistance to deformation. 57 In all other gels a strain thinning behaviour is observed, in which as strain is increased polymer chains disentangle to align with the direction of flow.…”