Highly Stretchable and Highly Resilient Polymer–Clay Nanocomposite Hydrogels with Low Hysteresis

Abstract

Highly stretchable and highly resilient polymer-clay nanocomposite hydrogels were synthesized by in situ polymerization of acrylamide in the presence of pristine montmorillonite (MMT) or chitosan-treated MMT nanoplatelets at an elevated temperature. Both nanocomposite hydrogels can be stretched to a strain of no less than 1290%. The treatment of clay with chitosan improves the tensile strength, elongation at break, and energy at break of the nanocomposite hydrogel by 237%, 102%, and 389%, respectively, due to the strong chitosan-MMT electrostatic interaction and the grafting of polyacrylamide onto chitosan chains. Both hydrogels display excellent resilience with low hysteresis; with a maximum tensile strain of 50%, ultralow hysteresis is found, while, with a maximum strain of 500%, both hydrogels fully recover their original state in just 1 min. The superb resilience of the nanocomposite hydrogels is attributed to the strong interactions within the hydrogels brought by chain branching, multiple hydrogen bonding, covalent bonding, and/or electrostatic force. The hydrogels can be fabricated into different shapes and forms, including microfibers spun using pressurized gyration, which may find a variety of potential applications in particular in healthcare.

Developments in Pressurized Gyration for the Mass Production of Polymeric Fibers

“…Not only this, the cross‐linking density and inter‐crosslinking molecular weight cannot be controlled separately. When the concentration of the cross‐linker is high, heterogeneous aggregation of the cross‐linking points occurs . Hydrogels that have been chemically cross‐linked are thus limited in terms of their morphology, mechanical strength, and optical transparency .…”

“…When the concentration of the cross-linker is high, heterogeneous aggregation of the crosslinking points occurs. [95] Hydrogels that have been chemically cross-linked are thus limited in terms of their morphology, mechanical strength, and optical transparency. [96] Although ultra-stretchable, self-healing, and tough hydrogels can be synthesized through physically cross-linking, for example, from polyacrylamide-montmorillonite (PAM-MMT), it is difficult to achieve low hysteresis, and therefore optimum mechanical properties, as some of the organic-inorganic cross-links will break.…”

“…Our laboratory, in association with Chen and coworkers, used PG to fabricate PAM-clay nanocomposite hydrogel fibers, exhibiting low hysteresis. [95] To do this, in situ polymerization of acrylamide (AM) in the presence of MMT or chitosan− treated MMT (CHI−MMT) was conducted at 60 °C, instead of with a catalyst, to allow for chain grafting and branching. The radical initiator attacked the hydroxyl groups of the polysaccharide chains to generate alkoxy radicals, initiating polymerization of AM.…”

Nanoparticle–Polymer Synergies in Nanocomposite Hydrogels: From Design to Application

“…And then the in situ polymerizations of hydrogels were occurred to obtain hydrogels with stable structure and excellent mechanical properties. In situ growth of NC gels is usually suitable for NPs with intrinsic functions but hardly surface modified, for example, polyaniline NPs, metal and metal‐oxide NPs . Physical mixing is a simple route to compound NC gels by polymer and NPs directly.…”

“…Typically, due to the reversible physical interactions between polymers and NPs, the overload mechanical stress on the NC gels could be effectively dissipated by spreading along with the polymer chains mutually rather than concentrated. As a result, the NC gel is less likely to form micro cracks under mechanical stress, which avoids widespread failure and endows the NC gel with good mechanical properties …”