Recent advances in clay mineral-containing nanocomposite hydrogels

Abstract

Clay mineral-containing nanocomposite hydrogels have been proven to have exceptional composition, properties, and applications, and consequently have attracted a significant amount of research effort over the past few years. The objective of this paper is to summarize and evaluate scientific advances in clay mineral-containing nanocomposite hydrogels in terms of their specific preparation, formation mechanisms, properties, and applications, and to identify the prevailing challenges and future directions in the field. The state-of-the-art of existing technologies and insights into the exfoliation of layered clay minerals, in particular montmorillonite and LAPONITE s , are discussed first. The formation and structural characteristics of polymer/clay nanocomposite hydrogels made from in situ free radical polymerization, supramolecular assembly, and freezing-thawing cycles are then examined. Studies indicate that additional hydrogen bonding, electrostatic interactions, coordination bonds, hydrophobic interaction, and even covalent bonds could occur between the clay mineral nanoplatelets and polymer chains, thereby leading to the formation of unique three-dimensional networks. Accordingly, the hydrogels exhibit exceptional optical and mechanical properties, swelling-deswelling behavior, and stimuli-responsiveness, reflecting the remarkable effects of clay minerals. With the pivotal roles of clay minerals in clay mineral-containing nanocomposite hydrogels, the nanocomposite hydrogels possess great potential as superabsorbents, drug vehicles, tissue scaffolds, wound dressing, and biosensors. Future studies should lay emphasis on the formation mechanisms with in-depth insights into interfacial interactions, the tactical functionalization of clay minerals and polymers for desired properties, and expanding of their applications.

Photo‐Induced Hydrogel Formation Based on g‐C3N4 Nanosheets with Self‐Cross‐Linked 3D Framework for UV Protection Application

“…And therefore varied properties may be achieved using different polymers to form hydrogels, as well as cross‐linking actions. Meanwhile, the functionality of hydrogels can also be facilely modulated by modifying different compositions on the hydrogel skeletons …”

Sudanese Clays for Heterogenous Methanolysis of Castor Oil

“…The rest of the hydroxyl groups bands shifted to the lower frequency after acid modification [7]. For JQ, after acid modification three new bands appeared.…”

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

“…Three main strategies have been widely used to introduce NPs into NC hydrogels including in situ polymerization, in situ growth of the NPs, and physical mixing . In situ polymerization is suitable for NPs with polar group on surface such as carboxyl (‐COOH), hydroxyl (‐OH), and amino (‐NH 2 ), for example, laponite, graphene oxide, dendrimers, which can form strong hydrogen bonds and electrostatic interactions with monomers . And then the in situ polymerizations of hydrogels were occurred to obtain hydrogels with stable structure and excellent mechanical properties.…”

“…Clays, a series of minerals with diverse dimensions, such as SiO 2 (0D), halloysite‐nanotubes (1D), montmorillonite (2D), and synthetic hectorite (2D), are extensively used as nanofillers in NC gels . One frequently used material is clay nanoplatelets, such as montmorillonite (MMT) and synthetic hectorite (laponite).…”

“…Specifically, the conformational shift of the PNIPAAm chain from hydrophilic coil to hydrophobic globular formation upon heating above LCST (≈32 °C) is significantly confined by clay. The main reason is that with the increasing content of clay, which forms hydrophilic edges and hydrophobic surfaces, the hydrophilic–hydrophobic balance of PNIPAAm hydrogel becomes influenced by the clay fractions, and as a result, the LCST of PNIPAAm/clay NC gels is higher than that of normal PNIPAAm hydrogel …”