Cellulose Nanocrystals Mechanical Reinforcement in Composite Hydrogels with Multiple Cross-Links: Correlations between Dissipation Properties and Deformation Mechanisms

Abstract

Nanocomposites have drawn a great interest in materials science of elastomers in recent years, and tailoring interfacial interactions between fillers and polymer matrix plays a critical role in improving their mechanical properties. The synthetic platform of tough and stretchable cellulose nanocrystal−poly(acrylamide) (CNC−PAM) composite hydrogels was proposed and applied here to unravel the role of covalent network in PAM and physical interactions by CNC surface adsorption. The attractive physical interactions in the network were considered to increase the fracture strength of the hydrogels via reversible adsorption−desorption processes on the CNC surface. Stress-sensitive characteristic shifts of the Raman peak located at 1095 cm −1 indicated an efficient load transfer across the interface, where the tensile modulus was higher than the compression modulus. In situ transmission electron microscopy observation allowed to demystify the composites deformation process and interfacial bridging between CNC and polymer matrix. A detailed comparison of strain rate effect on large strain dissipation indicated that the viscoelastic behavior of the hydrogels varied remarkably over strain rates, ranging from little hysteresis at low strain rates to highly dissipative at high strain rates, suggesting a new, slow relaxation mode, most likely due to interfacial adsorption of polymer chains on the CNC surfaces. This study showed that polymer chains desorbed from the CNC surface under periodic strains would entangle with the free chains after the rest time via conformational rearrangements, consequently triggering a recovering mechanism during multiple crazing and shear relaxation processes.

Surface modification of polyvinyl alcohol (PVA)/polyacrylamide (PAAm) hydrogels with polydopamine and REDV for improved applicability

“…For a small‐diameter vascular graft, such a change may lead to acute thrombosis at the beginning of implantation. Therefore, the equilibrium swelling ratio should be investigated for a hydrogel small‐diameter vascular graft . Figure showed the results of the equilibrium swelling ratios of the PVA/PAAm, H‐PDA, and H‐PDA‐REDV hydrogels.…”

“…Therefore, the equilibrium swelling ratio should be investigated for a hydrogel small-diameter vascular graft. [44][45][46] Figure 5 showed the results of the equilibrium swelling ratios of the PVA/PAAm, H-PDA, and H-PDA-REDV hydrogels. In particular, the hydrogels maintained a constant size in the aqueous solution for 48 h, regardless of PDA or PDA-REDV coating, suggesting that they could keep a changeless inner caliber while being used as a small diameter-vascular graft.…”

Enhancing Mechanical Performance of a Covalent Self-Healing Material by Sacrificial Noncovalent Bonds

“…24,25 Reversible sacrificial bonds commonly used as transient cross-linkers in synthetic materials include ionic, 26 metal-ligand, 27 and hydrogen-bonding interactions. [28][29][30][31] Whereas a few covalent self-healing polymers contain sacrificial bonds, 12 to the best of our knowledge, such sacrificial bond strategy has not been carefully studied nor purposely used to enhance the mechanical properties of self-healing polymers. Herein, we demonstrate that incorporation of a simple, sacrificial hydrogen-bonding amide functionality dramatically enhances the mechanical performance of a covalent self-healing polymeric network ( Figure 1).…”

Chain Entanglements and Hydrogen Bonds in Carbopol Microgel Reinforced Hydrogel

“…Cyclic tensile tests were performed to investigate the energy dissipation mechanism. As shown in Figure b, no hysteresis loop was observed when ε max ≤ 1.2, implying that no bond breaking occurred in the elastic deformation region . A significant hysteresis loop appeared when ε max > 1.2.…”

“…As shown in Figure 2 b, no hysteresis loop was observed when ε max ≤ 1.2, implying that no bond breaking occurred in the elastic deformation region. [ 30,31 ] A signifi cant hysteresis loop appeared Macromol. Chem.…”