Thermoresponsive Toughening with Crack Bifurcation in Phase‐Separated Hydrogels under Isochoric Conditions

Abstract

A novel mode of gel toughening displaying crack bifurcation is highlighted in phase-separated hydrogels. By exploring original covalent network topologies, phase-separated gels under isochoric conditions demonstrate advanced thermoresponsive mechanical properties: excellent fatigue resistance, self-healing, and remarkable fracture energies. Beyond the phase-transition temperature, the fracture proceeds by a systematic crack-bifurcation process, unreported so far in gels.

Underwater Adhesion of Multiresponsive Complex Coacervates

“…However, when performing a salt switch, the adhesive needs to be stretched much more in order to completely disentangle the polyelectrolyte backbones due to their higher molecular weight than the PNIPAM chains. Similar observations were reported by Guo et al when exploring the effect of the architecture of PNIPAM‐based hydrogels on fracture properties, highlighting that the microphase separated structure has a dramatic impact on large strain behavior.…”

Hydrogels with Dual Thermoresponsive Mechanical Performance

“…[29] Indeed, by using only miscible organic solvents, this new synthesis procedure is less time-consuming by reducing the number of purification steps and avoiding the presence of ionic group (see procedure of NAGA synthesis, Figures S1-S3 and Table S1, Supporting (Figure 1). [16,17] Despite the phase separation process, PAN hydrogel retains almost the same swelling ratio than in the preparation state both at high (T40 °C, Q e Q 0 =6) and low (T=5 °C, Q e 7)…”

“…These hydrogels can retain a high level of water (more than 80 wt%) on both sides of the transition temperature. [16,17] To achieve this, lower critical solution temperature (LCST) polymer chains such as PNIPAm and hydrophilic poly(N,N-dimethylacrylamide) (PDMA) were combined into the same cross-linked architecture. Within this network, the hydrophilic counterpart allows to maintain a high level of hydration, even above the phase transition temperature of the PNIPAm.…”

Bulk Energy Dissipation Mechanism for the Fracture of Tough and Self-Healing Hydrogels

“…By dialysis of small counter-ions and co-ions in pure water, ionic associations between opposite charges on the polymer chains, both intra-and inter-chains, are switched on, which gives a micro-phase separated PA hydrogels containing ~ 50 wt% of water. 10, [34][35][36] In our previous paper, the PA hydrogels were described by a dichotomic molecular picture of the elastic network with weak bonds and strong bonds, where upon the weak bonds can break to dissipate energy and reform to impart self-healing, and strong bonds can maintain the integrity of the physical hydrogel over much longer timescale. Given the micro phase separated structure and the wide distribution of relaxation time in the dynamic rheological spectrum, however, this dichotomic network picture is over 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 structures.…”

“…Given the micro phase separated structure and the wide distribution of relaxation time in the dynamic rheological spectrum, however, this dichotomic network picture is over 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 structures. [34][35][36] In this work, we intend to use a more global viscoelastic picture to discuss the mechanical behaviors of the PA hydrogels.…”